[PATCHv2 00/13] x86/tdx: Add kexec support

[PATCHv2 00/13] x86/tdx: Add kexec support

[Kirill A. Shutemov]

The patchset adds bits and pieces to get kexec (and crashkernel) work on
TDX guest.

The last patch implements CPU offlining according to the approved ACPI
spec change poposal[1]. It unlocks kexec with all CPUs visible in the target
kernel. It requires BIOS-side enabling. If it missing we fallback to booting
2nd kernel with single CPU.

Please review. I would be glad for any feedback.

v2:
  - Rework how unsharing hook ups into kexec codepath;
  - Rework kvmclock_disable() fix based on Sean's;
  - s/cpu_hotplug_not_supported()/cpu_hotplug_disable_offlining()/;
  - use play_dead_common() to implement acpi_mp_play_dead();
  - cond_resched() in tdx_shared_memory_show();
  - s/target kernel/second kernel/;
  - Update commit messages and comments;

[1] https://lore.kernel.org/all/13356251.uLZWGnKmhe@kreacher

Kirill A. Shutemov (13):
  x86/acpi: Extract ACPI MADT wakeup code into a separate file
  kernel/cpu: Add support for declaring CPU offlining not supported
  cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup
  x86/kvm: Do not try to disable kvmclock if it was not enabled
  x86/kexec: Keep CR4.MCE set during kexec for TDX guest
  x86/mm: Make x86_platform.guest.enc_status_change_*() return errno
  x86/mm: Return correct level from lookup_address() if pte is none
  x86/tdx: Account shared memory
  x86/tdx: Convert shared memory back to private on kexec
  x86/mm: Make e820_end_ram_pfn() cover E820_TYPE_ACPI ranges
  x86/acpi: Do not attempt to bring up secondary CPUs in kexec case
  x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure
  x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

 arch/x86/Kconfig                     |   7 +
 arch/x86/coco/core.c                 |   1 -
 arch/x86/coco/tdx/kexec.c            |   0
 arch/x86/coco/tdx/tdx.c              | 205 +++++++++++++++++++-
 arch/x86/hyperv/ivm.c                |   9 +-
 arch/x86/include/asm/acpi.h          |   5 +
 arch/x86/include/asm/pgtable_types.h |   1 +
 arch/x86/include/asm/x86_init.h      |   5 +-
 arch/x86/kernel/acpi/Makefile        |  11 +-
 arch/x86/kernel/acpi/boot.c          |  88 +--------
 arch/x86/kernel/acpi/madt.S          |  24 +++
 arch/x86/kernel/acpi/madt_wakeup.c   | 267 +++++++++++++++++++++++++++
 arch/x86/kernel/crash.c              |   4 +
 arch/x86/kernel/e820.c               |   9 +-
 arch/x86/kernel/kvmclock.c           |  12 +-
 arch/x86/kernel/reboot.c             |   5 +
 arch/x86/kernel/relocate_kernel_64.S |   5 +
 arch/x86/kernel/x86_init.c           |   4 +-
 arch/x86/mm/mem_encrypt_amd.c        |   8 +-
 arch/x86/mm/pat/set_memory.c         |  17 +-
 include/acpi/actbl2.h                |  19 +-
 include/linux/cc_platform.h          |  10 -
 include/linux/cpu.h                  |   2 +
 kernel/cpu.c                         |  12 +-
 24 files changed, 586 insertions(+), 144 deletions(-)
 create mode 100644 arch/x86/coco/tdx/kexec.c
 create mode 100644 arch/x86/kernel/acpi/madt.S
 create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c

-- 
2.41.0

[PATCHv2 00/13] x86/tdx: Add kexec support

[Kirill A. Shutemov]

The patchset adds bits and pieces to get kexec (and crashkernel) work on
TDX guest.

The last patch implements CPU offlining according to the approved ACPI
spec change poposal[1]. It unlocks kexec with all CPUs visible in the target
kernel. It requires BIOS-side enabling. If it missing we fallback to booting
2nd kernel with single CPU.

Please review. I would be glad for any feedback.

v2:
  - Rework how unsharing hook ups into kexec codepath;
  - Rework kvmclock_disable() fix based on Sean's;
  - s/cpu_hotplug_not_supported()/cpu_hotplug_disable_offlining()/;
  - use play_dead_common() to implement acpi_mp_play_dead();
  - cond_resched() in tdx_shared_memory_show();
  - s/target kernel/second kernel/;
  - Update commit messages and comments;

[1] https://lore.kernel.org/all/13356251.uLZWGnKmhe@kreacher

Kirill A. Shutemov (13):
  x86/acpi: Extract ACPI MADT wakeup code into a separate file
  kernel/cpu: Add support for declaring CPU offlining not supported
  cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup
  x86/kvm: Do not try to disable kvmclock if it was not enabled
  x86/kexec: Keep CR4.MCE set during kexec for TDX guest
  x86/mm: Make x86_platform.guest.enc_status_change_*() return errno
  x86/mm: Return correct level from lookup_address() if pte is none
  x86/tdx: Account shared memory
  x86/tdx: Convert shared memory back to private on kexec
  x86/mm: Make e820_end_ram_pfn() cover E820_TYPE_ACPI ranges
  x86/acpi: Do not attempt to bring up secondary CPUs in kexec case
  x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure
  x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

 arch/x86/Kconfig                     |   7 +
 arch/x86/coco/core.c                 |   1 -
 arch/x86/coco/tdx/kexec.c            |   0
 arch/x86/coco/tdx/tdx.c              | 205 +++++++++++++++++++-
 arch/x86/hyperv/ivm.c                |   9 +-
 arch/x86/include/asm/acpi.h          |   5 +
 arch/x86/include/asm/pgtable_types.h |   1 +
 arch/x86/include/asm/x86_init.h      |   5 +-
 arch/x86/kernel/acpi/Makefile        |  11 +-
 arch/x86/kernel/acpi/boot.c          |  88 +--------
 arch/x86/kernel/acpi/madt.S          |  24 +++
 arch/x86/kernel/acpi/madt_wakeup.c   | 267 +++++++++++++++++++++++++++
 arch/x86/kernel/crash.c              |   4 +
 arch/x86/kernel/e820.c               |   9 +-
 arch/x86/kernel/kvmclock.c           |  12 +-
 arch/x86/kernel/reboot.c             |   5 +
 arch/x86/kernel/relocate_kernel_64.S |   5 +
 arch/x86/kernel/x86_init.c           |   4 +-
 arch/x86/mm/mem_encrypt_amd.c        |   8 +-
 arch/x86/mm/pat/set_memory.c         |  17 +-
 include/acpi/actbl2.h                |  19 +-
 include/linux/cc_platform.h          |  10 -
 include/linux/cpu.h                  |   2 +
 kernel/cpu.c                         |  12 +-
 24 files changed, 586 insertions(+), 144 deletions(-)
 create mode 100644 arch/x86/coco/tdx/kexec.c
 create mode 100644 arch/x86/kernel/acpi/madt.S
 create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c

-- 
2.41.0


_______________________________________________
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kexec@lists.infradead.org
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[PATCHv2 01/13] x86/acpi: Extract ACPI MADT wakeup code into a separate file

[Kirill A. Shutemov]

In order to prepare for the expansion of support for the ACPI MADT
wakeup method, move the relevant code into a separate file.

Introduce a new configuration option to clearly indicate dependencies
without the use of ifdefs.

There have been no functional changes.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/Kconfig                   |  7 +++
 arch/x86/include/asm/acpi.h        |  5 ++
 arch/x86/kernel/acpi/Makefile      | 11 ++--
 arch/x86/kernel/acpi/boot.c        | 86 +-----------------------------
 arch/x86/kernel/acpi/madt_wakeup.c | 81 ++++++++++++++++++++++++++++
 5 files changed, 100 insertions(+), 90 deletions(-)
 create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 799102f4d909..9957a73bb386 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1108,6 +1108,13 @@ config X86_LOCAL_APIC
 	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
 	select IRQ_DOMAIN_HIERARCHY
 
+config X86_ACPI_MADT_WAKEUP
+	def_bool y
+	depends on X86_64
+	depends on ACPI
+	depends on SMP
+	depends on X86_LOCAL_APIC
+
 config X86_IO_APIC
 	def_bool y
 	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index c8a7fc23f63c..b536b5a6a57b 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -73,6 +73,11 @@ static inline bool acpi_skip_set_wakeup_address(void)
 
 #define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
 
+union acpi_subtable_headers;
+
+int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
+			      const unsigned long end);
+
 /*
  * Check if the CPU can handle C2 and deeper
  */
diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
index fc17b3f136fe..8c7329c88a75 100644
--- a/arch/x86/kernel/acpi/Makefile
+++ b/arch/x86/kernel/acpi/Makefile
@@ -1,11 +1,12 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_ACPI)		+= boot.o
-obj-$(CONFIG_ACPI_SLEEP)	+= sleep.o wakeup_$(BITS).o
-obj-$(CONFIG_ACPI_APEI)		+= apei.o
-obj-$(CONFIG_ACPI_CPPC_LIB)	+= cppc.o
+obj-$(CONFIG_ACPI)			+= boot.o
+obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
+obj-$(CONFIG_ACPI_APEI)			+= apei.o
+obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
+obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
 
 ifneq ($(CONFIG_ACPI_PROCESSOR),)
-obj-y				+= cstate.o
+obj-y					+= cstate.o
 endif
 
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 2a0ea38955df..111bd226ad99 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -66,13 +66,6 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 static bool acpi_support_online_capable;
 #endif
 
-#ifdef CONFIG_X86_64
-/* Physical address of the Multiprocessor Wakeup Structure mailbox */
-static u64 acpi_mp_wake_mailbox_paddr;
-/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
-static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
-#endif
-
 #ifdef CONFIG_X86_IO_APIC
 /*
  * Locks related to IOAPIC hotplug
@@ -357,60 +350,6 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
 
 	return 0;
 }
-
-#ifdef CONFIG_X86_64
-static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
-{
-	/*
-	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
-	 *
-	 * Wakeup of secondary CPUs is fully serialized in the core code.
-	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
-	 */
-	if (!acpi_mp_wake_mailbox) {
-		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
-						sizeof(*acpi_mp_wake_mailbox),
-						MEMREMAP_WB);
-	}
-
-	/*
-	 * Mailbox memory is shared between the firmware and OS. Firmware will
-	 * listen on mailbox command address, and once it receives the wakeup
-	 * command, the CPU associated with the given apicid will be booted.
-	 *
-	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
-	 * firmware before the wakeup command is visible.  smp_store_release()
-	 * ensures ordering and visibility.
-	 */
-	acpi_mp_wake_mailbox->apic_id	    = apicid;
-	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
-	smp_store_release(&acpi_mp_wake_mailbox->command,
-			  ACPI_MP_WAKE_COMMAND_WAKEUP);
-
-	/*
-	 * Wait for the CPU to wake up.
-	 *
-	 * The CPU being woken up is essentially in a spin loop waiting to be
-	 * woken up. It should not take long for it wake up and acknowledge by
-	 * zeroing out ->command.
-	 *
-	 * ACPI specification doesn't provide any guidance on how long kernel
-	 * has to wait for a wake up acknowledgement. It also doesn't provide
-	 * a way to cancel a wake up request if it takes too long.
-	 *
-	 * In TDX environment, the VMM has control over how long it takes to
-	 * wake up secondary. It can postpone scheduling secondary vCPU
-	 * indefinitely. Giving up on wake up request and reporting error opens
-	 * possible attack vector for VMM: it can wake up a secondary CPU when
-	 * kernel doesn't expect it. Wait until positive result of the wake up
-	 * request.
-	 */
-	while (READ_ONCE(acpi_mp_wake_mailbox->command))
-		cpu_relax();
-
-	return 0;
-}
-#endif /* CONFIG_X86_64 */
 #endif /* CONFIG_X86_LOCAL_APIC */
 
 #ifdef CONFIG_X86_IO_APIC
@@ -1160,29 +1099,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
 	}
 	return 0;
 }
-
-#ifdef CONFIG_X86_64
-static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
-				     const unsigned long end)
-{
-	struct acpi_madt_multiproc_wakeup *mp_wake;
-
-	if (!IS_ENABLED(CONFIG_SMP))
-		return -ENODEV;
-
-	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
-	if (BAD_MADT_ENTRY(mp_wake, end))
-		return -EINVAL;
-
-	acpi_table_print_madt_entry(&header->common);
-
-	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
-
-	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
-
-	return 0;
-}
-#endif				/* CONFIG_X86_64 */
 #endif				/* CONFIG_X86_LOCAL_APIC */
 
 #ifdef	CONFIG_X86_IO_APIC
@@ -1379,7 +1295,7 @@ static void __init acpi_process_madt(void)
 				smp_found_config = 1;
 			}
 
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_ACPI_MADT_WAKEUP
 			/*
 			 * Parse MADT MP Wake entry.
 			 */
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
new file mode 100644
index 000000000000..58cdfc0b6c0a
--- /dev/null
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -0,0 +1,81 @@
+#include <linux/acpi.h>
+#include <linux/io.h>
+#include <asm/apic.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
+/* Physical address of the Multiprocessor Wakeup Structure mailbox */
+static u64 acpi_mp_wake_mailbox_paddr;
+
+/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
+static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
+
+static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
+{
+	/*
+	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
+	 *
+	 * Wakeup of secondary CPUs is fully serialized in the core code.
+	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
+	 */
+	if (!acpi_mp_wake_mailbox) {
+		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
+						sizeof(*acpi_mp_wake_mailbox),
+						MEMREMAP_WB);
+	}
+
+	/*
+	 * Mailbox memory is shared between the firmware and OS. Firmware will
+	 * listen on mailbox command address, and once it receives the wakeup
+	 * command, the CPU associated with the given apicid will be booted.
+	 *
+	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
+	 * firmware before the wakeup command is visible.  smp_store_release()
+	 * ensures ordering and visibility.
+	 */
+	acpi_mp_wake_mailbox->apic_id	    = apicid;
+	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
+	smp_store_release(&acpi_mp_wake_mailbox->command,
+			  ACPI_MP_WAKE_COMMAND_WAKEUP);
+
+	/*
+	 * Wait for the CPU to wake up.
+	 *
+	 * The CPU being woken up is essentially in a spin loop waiting to be
+	 * woken up. It should not take long for it wake up and acknowledge by
+	 * zeroing out ->command.
+	 *
+	 * ACPI specification doesn't provide any guidance on how long kernel
+	 * has to wait for a wake up acknowledgement. It also doesn't provide
+	 * a way to cancel a wake up request if it takes too long.
+	 *
+	 * In TDX environment, the VMM has control over how long it takes to
+	 * wake up secondary. It can postpone scheduling secondary vCPU
+	 * indefinitely. Giving up on wake up request and reporting error opens
+	 * possible attack vector for VMM: it can wake up a secondary CPU when
+	 * kernel doesn't expect it. Wait until positive result of the wake up
+	 * request.
+	 */
+	while (READ_ONCE(acpi_mp_wake_mailbox->command))
+		cpu_relax();
+
+	return 0;
+}
+
+int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
+			      const unsigned long end)
+{
+	struct acpi_madt_multiproc_wakeup *mp_wake;
+
+	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
+	if (BAD_MADT_ENTRY(mp_wake, end))
+		return -EINVAL;
+
+	acpi_table_print_madt_entry(&header->common);
+
+	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
+
+	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
+
+	return 0;
+}
-- 
2.41.0

[PATCHv2 01/13] x86/acpi: Extract ACPI MADT wakeup code into a separate file

[Kirill A. Shutemov]

In order to prepare for the expansion of support for the ACPI MADT
wakeup method, move the relevant code into a separate file.

Introduce a new configuration option to clearly indicate dependencies
without the use of ifdefs.

There have been no functional changes.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/Kconfig                   |  7 +++
 arch/x86/include/asm/acpi.h        |  5 ++
 arch/x86/kernel/acpi/Makefile      | 11 ++--
 arch/x86/kernel/acpi/boot.c        | 86 +-----------------------------
 arch/x86/kernel/acpi/madt_wakeup.c | 81 ++++++++++++++++++++++++++++
 5 files changed, 100 insertions(+), 90 deletions(-)
 create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 799102f4d909..9957a73bb386 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1108,6 +1108,13 @@ config X86_LOCAL_APIC
 	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
 	select IRQ_DOMAIN_HIERARCHY
 
+config X86_ACPI_MADT_WAKEUP
+	def_bool y
+	depends on X86_64
+	depends on ACPI
+	depends on SMP
+	depends on X86_LOCAL_APIC
+
 config X86_IO_APIC
 	def_bool y
 	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index c8a7fc23f63c..b536b5a6a57b 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -73,6 +73,11 @@ static inline bool acpi_skip_set_wakeup_address(void)
 
 #define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
 
+union acpi_subtable_headers;
+
+int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
+			      const unsigned long end);
+
 /*
  * Check if the CPU can handle C2 and deeper
  */
diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
index fc17b3f136fe..8c7329c88a75 100644
--- a/arch/x86/kernel/acpi/Makefile
+++ b/arch/x86/kernel/acpi/Makefile
@@ -1,11 +1,12 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_ACPI)		+= boot.o
-obj-$(CONFIG_ACPI_SLEEP)	+= sleep.o wakeup_$(BITS).o
-obj-$(CONFIG_ACPI_APEI)		+= apei.o
-obj-$(CONFIG_ACPI_CPPC_LIB)	+= cppc.o
+obj-$(CONFIG_ACPI)			+= boot.o
+obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
+obj-$(CONFIG_ACPI_APEI)			+= apei.o
+obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
+obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
 
 ifneq ($(CONFIG_ACPI_PROCESSOR),)
-obj-y				+= cstate.o
+obj-y					+= cstate.o
 endif
 
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 2a0ea38955df..111bd226ad99 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -66,13 +66,6 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 static bool acpi_support_online_capable;
 #endif
 
-#ifdef CONFIG_X86_64
-/* Physical address of the Multiprocessor Wakeup Structure mailbox */
-static u64 acpi_mp_wake_mailbox_paddr;
-/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
-static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
-#endif
-
 #ifdef CONFIG_X86_IO_APIC
 /*
  * Locks related to IOAPIC hotplug
@@ -357,60 +350,6 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
 
 	return 0;
 }
-
-#ifdef CONFIG_X86_64
-static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
-{
-	/*
-	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
-	 *
-	 * Wakeup of secondary CPUs is fully serialized in the core code.
-	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
-	 */
-	if (!acpi_mp_wake_mailbox) {
-		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
-						sizeof(*acpi_mp_wake_mailbox),
-						MEMREMAP_WB);
-	}
-
-	/*
-	 * Mailbox memory is shared between the firmware and OS. Firmware will
-	 * listen on mailbox command address, and once it receives the wakeup
-	 * command, the CPU associated with the given apicid will be booted.
-	 *
-	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
-	 * firmware before the wakeup command is visible.  smp_store_release()
-	 * ensures ordering and visibility.
-	 */
-	acpi_mp_wake_mailbox->apic_id	    = apicid;
-	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
-	smp_store_release(&acpi_mp_wake_mailbox->command,
-			  ACPI_MP_WAKE_COMMAND_WAKEUP);
-
-	/*
-	 * Wait for the CPU to wake up.
-	 *
-	 * The CPU being woken up is essentially in a spin loop waiting to be
-	 * woken up. It should not take long for it wake up and acknowledge by
-	 * zeroing out ->command.
-	 *
-	 * ACPI specification doesn't provide any guidance on how long kernel
-	 * has to wait for a wake up acknowledgement. It also doesn't provide
-	 * a way to cancel a wake up request if it takes too long.
-	 *
-	 * In TDX environment, the VMM has control over how long it takes to
-	 * wake up secondary. It can postpone scheduling secondary vCPU
-	 * indefinitely. Giving up on wake up request and reporting error opens
-	 * possible attack vector for VMM: it can wake up a secondary CPU when
-	 * kernel doesn't expect it. Wait until positive result of the wake up
-	 * request.
-	 */
-	while (READ_ONCE(acpi_mp_wake_mailbox->command))
-		cpu_relax();
-
-	return 0;
-}
-#endif /* CONFIG_X86_64 */
 #endif /* CONFIG_X86_LOCAL_APIC */
 
 #ifdef CONFIG_X86_IO_APIC
@@ -1160,29 +1099,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
 	}
 	return 0;
 }
-
-#ifdef CONFIG_X86_64
-static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
-				     const unsigned long end)
-{
-	struct acpi_madt_multiproc_wakeup *mp_wake;
-
-	if (!IS_ENABLED(CONFIG_SMP))
-		return -ENODEV;
-
-	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
-	if (BAD_MADT_ENTRY(mp_wake, end))
-		return -EINVAL;
-
-	acpi_table_print_madt_entry(&header->common);
-
-	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
-
-	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
-
-	return 0;
-}
-#endif				/* CONFIG_X86_64 */
 #endif				/* CONFIG_X86_LOCAL_APIC */
 
 #ifdef	CONFIG_X86_IO_APIC
@@ -1379,7 +1295,7 @@ static void __init acpi_process_madt(void)
 				smp_found_config = 1;
 			}
 
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_ACPI_MADT_WAKEUP
 			/*
 			 * Parse MADT MP Wake entry.
 			 */
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
new file mode 100644
index 000000000000..58cdfc0b6c0a
--- /dev/null
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -0,0 +1,81 @@
+#include <linux/acpi.h>
+#include <linux/io.h>
+#include <asm/apic.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
+/* Physical address of the Multiprocessor Wakeup Structure mailbox */
+static u64 acpi_mp_wake_mailbox_paddr;
+
+/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
+static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
+
+static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
+{
+	/*
+	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
+	 *
+	 * Wakeup of secondary CPUs is fully serialized in the core code.
+	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
+	 */
+	if (!acpi_mp_wake_mailbox) {
+		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
+						sizeof(*acpi_mp_wake_mailbox),
+						MEMREMAP_WB);
+	}
+
+	/*
+	 * Mailbox memory is shared between the firmware and OS. Firmware will
+	 * listen on mailbox command address, and once it receives the wakeup
+	 * command, the CPU associated with the given apicid will be booted.
+	 *
+	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
+	 * firmware before the wakeup command is visible.  smp_store_release()
+	 * ensures ordering and visibility.
+	 */
+	acpi_mp_wake_mailbox->apic_id	    = apicid;
+	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
+	smp_store_release(&acpi_mp_wake_mailbox->command,
+			  ACPI_MP_WAKE_COMMAND_WAKEUP);
+
+	/*
+	 * Wait for the CPU to wake up.
+	 *
+	 * The CPU being woken up is essentially in a spin loop waiting to be
+	 * woken up. It should not take long for it wake up and acknowledge by
+	 * zeroing out ->command.
+	 *
+	 * ACPI specification doesn't provide any guidance on how long kernel
+	 * has to wait for a wake up acknowledgement. It also doesn't provide
+	 * a way to cancel a wake up request if it takes too long.
+	 *
+	 * In TDX environment, the VMM has control over how long it takes to
+	 * wake up secondary. It can postpone scheduling secondary vCPU
+	 * indefinitely. Giving up on wake up request and reporting error opens
+	 * possible attack vector for VMM: it can wake up a secondary CPU when
+	 * kernel doesn't expect it. Wait until positive result of the wake up
+	 * request.
+	 */
+	while (READ_ONCE(acpi_mp_wake_mailbox->command))
+		cpu_relax();
+
+	return 0;
+}
+
+int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
+			      const unsigned long end)
+{
+	struct acpi_madt_multiproc_wakeup *mp_wake;
+
+	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
+	if (BAD_MADT_ENTRY(mp_wake, end))
+		return -EINVAL;
+
+	acpi_table_print_madt_entry(&header->common);
+
+	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
+
+	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
+
+	return 0;
+}
-- 
2.41.0


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[PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up.

Currently offlining hotplug prevented based on the confidential
computing attribute which is set for Intel TDX. But TDX is not
the only possible user of the wake up method.

Introduce cpu_hotplug_not_supported() that can be called to indicate
that CPU offlining should be disabled.

This function is going to replace CC_ATTR_HOTPLUG_DISABLED for ACPI
MADT.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/cpu.h |  2 ++
 kernel/cpu.c        | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index f19f56501809..97832ced939d 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -132,6 +132,7 @@ extern void cpus_read_lock(void);
 extern void cpus_read_unlock(void);
 extern int  cpus_read_trylock(void);
 extern void lockdep_assert_cpus_held(void);
+extern void cpu_hotplug_disable_offlining(void);
 extern void cpu_hotplug_disable(void);
 extern void cpu_hotplug_enable(void);
 void clear_tasks_mm_cpumask(int cpu);
@@ -147,6 +148,7 @@ static inline void cpus_read_lock(void) { }
 static inline void cpus_read_unlock(void) { }
 static inline int  cpus_read_trylock(void) { return true; }
 static inline void lockdep_assert_cpus_held(void) { }
+static inline void cpu_hotplug_disable_offlining(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
 static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..faebee0050a2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -484,6 +484,8 @@ static int cpu_hotplug_disabled;
 
 DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
 
+static bool cpu_hotplug_offline_disabled;
+
 void cpus_read_lock(void)
 {
 	percpu_down_read(&cpu_hotplug_lock);
@@ -543,6 +545,14 @@ static void lockdep_release_cpus_lock(void)
 	rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
 }
 
+/* Declare CPU offlining not supported */
+void cpu_hotplug_disable_offlining(void)
+{
+	cpu_maps_update_begin();
+	cpu_hotplug_offline_disabled = true;
+	cpu_maps_update_done();
+}
+
 /*
  * Wait for currently running CPU hotplug operations to complete (if any) and
  * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
@@ -1507,7 +1517,8 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 	 * If the platform does not support hotplug, report it explicitly to
 	 * differentiate it from a transient offlining failure.
 	 */
-	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED))
+	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
+	    cpu_hotplug_offline_disabled)
 		return -EOPNOTSUPP;
 	if (cpu_hotplug_disabled)
 		return -EBUSY;
-- 
2.41.0

[PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up.

Currently offlining hotplug prevented based on the confidential
computing attribute which is set for Intel TDX. But TDX is not
the only possible user of the wake up method.

Introduce cpu_hotplug_not_supported() that can be called to indicate
that CPU offlining should be disabled.

This function is going to replace CC_ATTR_HOTPLUG_DISABLED for ACPI
MADT.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/cpu.h |  2 ++
 kernel/cpu.c        | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index f19f56501809..97832ced939d 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -132,6 +132,7 @@ extern void cpus_read_lock(void);
 extern void cpus_read_unlock(void);
 extern int  cpus_read_trylock(void);
 extern void lockdep_assert_cpus_held(void);
+extern void cpu_hotplug_disable_offlining(void);
 extern void cpu_hotplug_disable(void);
 extern void cpu_hotplug_enable(void);
 void clear_tasks_mm_cpumask(int cpu);
@@ -147,6 +148,7 @@ static inline void cpus_read_lock(void) { }
 static inline void cpus_read_unlock(void) { }
 static inline int  cpus_read_trylock(void) { return true; }
 static inline void lockdep_assert_cpus_held(void) { }
+static inline void cpu_hotplug_disable_offlining(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
 static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..faebee0050a2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -484,6 +484,8 @@ static int cpu_hotplug_disabled;
 
 DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
 
+static bool cpu_hotplug_offline_disabled;
+
 void cpus_read_lock(void)
 {
 	percpu_down_read(&cpu_hotplug_lock);
@@ -543,6 +545,14 @@ static void lockdep_release_cpus_lock(void)
 	rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
 }
 
+/* Declare CPU offlining not supported */
+void cpu_hotplug_disable_offlining(void)
+{
+	cpu_maps_update_begin();
+	cpu_hotplug_offline_disabled = true;
+	cpu_maps_update_done();
+}
+
 /*
  * Wait for currently running CPU hotplug operations to complete (if any) and
  * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
@@ -1507,7 +1517,8 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 	 * If the platform does not support hotplug, report it explicitly to
 	 * differentiate it from a transient offlining failure.
 	 */
-	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED))
+	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
+	    cpu_hotplug_offline_disabled)
 		return -EOPNOTSUPP;
 	if (cpu_hotplug_disabled)
 		return -EBUSY;
-- 
2.41.0


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[PATCHv2 03/13] cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up.

Currently hotplug prevented based on the confidential computing
attribute which is set for Intel TDX. But TDX is not the only possible
user of the wake up method.

Disable CPU offlining on ACPI MADT wakeup enumeration.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/core.c               |  1 -
 arch/x86/kernel/acpi/madt_wakeup.c |  3 +++
 include/linux/cc_platform.h        | 10 ----------
 kernel/cpu.c                       |  3 +--
 4 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index eeec9986570e..f07c3bb7deab 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -20,7 +20,6 @@ static bool noinstr intel_cc_platform_has(enum cc_attr attr)
 {
 	switch (attr) {
 	case CC_ATTR_GUEST_UNROLL_STRING_IO:
-	case CC_ATTR_HOTPLUG_DISABLED:
 	case CC_ATTR_GUEST_MEM_ENCRYPT:
 	case CC_ATTR_MEM_ENCRYPT:
 		return true;
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 58cdfc0b6c0a..4bc1d5106afd 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -1,4 +1,5 @@
 #include <linux/acpi.h>
+#include <linux/cpu.h>
 #include <linux/io.h>
 #include <asm/apic.h>
 #include <asm/barrier.h>
@@ -75,6 +76,8 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
 
+	cpu_hotplug_disable_offlining();
+
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
 	return 0;
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index cb0d6cd1c12f..d08dd65b5c43 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -80,16 +80,6 @@ enum cc_attr {
 	 * using AMD SEV-SNP features.
 	 */
 	CC_ATTR_GUEST_SEV_SNP,
-
-	/**
-	 * @CC_ATTR_HOTPLUG_DISABLED: Hotplug is not supported or disabled.
-	 *
-	 * The platform/OS is running as a guest/virtual machine does not
-	 * support CPU hotplug feature.
-	 *
-	 * Examples include TDX Guest.
-	 */
-	CC_ATTR_HOTPLUG_DISABLED,
 };
 
 #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
diff --git a/kernel/cpu.c b/kernel/cpu.c
index faebee0050a2..51c258f289ac 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1517,8 +1517,7 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 	 * If the platform does not support hotplug, report it explicitly to
 	 * differentiate it from a transient offlining failure.
 	 */
-	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
-	    cpu_hotplug_offline_disabled)
+	if (cpu_hotplug_offline_disabled)
 		return -EOPNOTSUPP;
 	if (cpu_hotplug_disabled)
 		return -EBUSY;
-- 
2.41.0

[PATCHv2 03/13] cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up.

Currently hotplug prevented based on the confidential computing
attribute which is set for Intel TDX. But TDX is not the only possible
user of the wake up method.

Disable CPU offlining on ACPI MADT wakeup enumeration.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/core.c               |  1 -
 arch/x86/kernel/acpi/madt_wakeup.c |  3 +++
 include/linux/cc_platform.h        | 10 ----------
 kernel/cpu.c                       |  3 +--
 4 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index eeec9986570e..f07c3bb7deab 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -20,7 +20,6 @@ static bool noinstr intel_cc_platform_has(enum cc_attr attr)
 {
 	switch (attr) {
 	case CC_ATTR_GUEST_UNROLL_STRING_IO:
-	case CC_ATTR_HOTPLUG_DISABLED:
 	case CC_ATTR_GUEST_MEM_ENCRYPT:
 	case CC_ATTR_MEM_ENCRYPT:
 		return true;
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 58cdfc0b6c0a..4bc1d5106afd 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -1,4 +1,5 @@
 #include <linux/acpi.h>
+#include <linux/cpu.h>
 #include <linux/io.h>
 #include <asm/apic.h>
 #include <asm/barrier.h>
@@ -75,6 +76,8 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
 
+	cpu_hotplug_disable_offlining();
+
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
 	return 0;
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index cb0d6cd1c12f..d08dd65b5c43 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -80,16 +80,6 @@ enum cc_attr {
 	 * using AMD SEV-SNP features.
 	 */
 	CC_ATTR_GUEST_SEV_SNP,
-
-	/**
-	 * @CC_ATTR_HOTPLUG_DISABLED: Hotplug is not supported or disabled.
-	 *
-	 * The platform/OS is running as a guest/virtual machine does not
-	 * support CPU hotplug feature.
-	 *
-	 * Examples include TDX Guest.
-	 */
-	CC_ATTR_HOTPLUG_DISABLED,
 };
 
 #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
diff --git a/kernel/cpu.c b/kernel/cpu.c
index faebee0050a2..51c258f289ac 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1517,8 +1517,7 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 	 * If the platform does not support hotplug, report it explicitly to
 	 * differentiate it from a transient offlining failure.
 	 */
-	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
-	    cpu_hotplug_offline_disabled)
+	if (cpu_hotplug_offline_disabled)
 		return -EOPNOTSUPP;
 	if (cpu_hotplug_disabled)
 		return -EBUSY;
-- 
2.41.0


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[PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Kirill A. Shutemov]

kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
present in the VM. It leads to write to a MSR that doesn't exist on some
configurations, namely in TDX guest:

	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)

kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
features.

Do not disable kvmclock if it was not enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/kvmclock.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index fb8f52149be9..f2fff625576d 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -24,8 +24,8 @@
 
 static int kvmclock __initdata = 1;
 static int kvmclock_vsyscall __initdata = 1;
-static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
-static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
+static int msr_kvm_system_time __ro_after_init;
+static int msr_kvm_wall_clock __ro_after_init;
 static u64 kvm_sched_clock_offset __ro_after_init;
 
 static int __init parse_no_kvmclock(char *arg)
@@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
 
 void kvmclock_disable(void)
 {
-	native_write_msr(msr_kvm_system_time, 0, 0);
+	if (msr_kvm_system_time)
+		native_write_msr(msr_kvm_system_time, 0, 0);
 }
 
 static void __init kvmclock_init_mem(void)
@@ -294,7 +295,10 @@ void __init kvmclock_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
 		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
 		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
-	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
+		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
+	} else {
 		return;
 	}
 
-- 
2.41.0

[PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Kirill A. Shutemov]

kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
present in the VM. It leads to write to a MSR that doesn't exist on some
configurations, namely in TDX guest:

	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)

kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
features.

Do not disable kvmclock if it was not enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/kvmclock.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index fb8f52149be9..f2fff625576d 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -24,8 +24,8 @@
 
 static int kvmclock __initdata = 1;
 static int kvmclock_vsyscall __initdata = 1;
-static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
-static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
+static int msr_kvm_system_time __ro_after_init;
+static int msr_kvm_wall_clock __ro_after_init;
 static u64 kvm_sched_clock_offset __ro_after_init;
 
 static int __init parse_no_kvmclock(char *arg)
@@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
 
 void kvmclock_disable(void)
 {
-	native_write_msr(msr_kvm_system_time, 0, 0);
+	if (msr_kvm_system_time)
+		native_write_msr(msr_kvm_system_time, 0, 0);
 }
 
 static void __init kvmclock_init_mem(void)
@@ -294,7 +295,10 @@ void __init kvmclock_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
 		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
 		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
-	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
+		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
+	} else {
 		return;
 	}
 
-- 
2.41.0


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[PATCHv2 05/13] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

[Kirill A. Shutemov]

TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
to #VE.

Use alternatives to keep the flag during kexec for TDX guests.

The change doesn't affect non-TDX-guest environments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..bea89814b48e 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,11 +145,16 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 * Set cr4 to a known state:
 	 *  - physical address extension enabled
 	 *  - 5-level paging, if it was enabled before
+	 *  - Machine check exception on TDX guest. Clearing MCE is not allowed
+	 *    in TDX guests.
 	 */
 	movl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
+1:
+	ALTERNATIVE "jmp 1f", "", X86_FEATURE_TDX_GUEST
+	orl	$X86_CR4_MCE, %eax
 1:
 	movq	%rax, %cr4
 
-- 
2.41.0


_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCHv2 05/13] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

[Kirill A. Shutemov]

TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
to #VE.

Use alternatives to keep the flag during kexec for TDX guests.

The change doesn't affect non-TDX-guest environments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..bea89814b48e 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,11 +145,16 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 * Set cr4 to a known state:
 	 *  - physical address extension enabled
 	 *  - 5-level paging, if it was enabled before
+	 *  - Machine check exception on TDX guest. Clearing MCE is not allowed
+	 *    in TDX guests.
 	 */
 	movl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
+1:
+	ALTERNATIVE "jmp 1f", "", X86_FEATURE_TDX_GUEST
+	orl	$X86_CR4_MCE, %eax
 1:
 	movq	%rax, %cr4
 
-- 
2.41.0

[PATCHv2 06/13] x86/mm: Make x86_platform.guest.enc_status_change_*() return errno

[Kirill A. Shutemov]

TDX is going to have more than one reason to fail
enc_status_change_prepare().

Change the callback to return errno instead of assuming -EIO;
enc_status_change_finish() changed too to keep the interface symmetric.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c         | 20 +++++++++++---------
 arch/x86/hyperv/ivm.c           |  9 +++------
 arch/x86/include/asm/x86_init.h |  4 ++--
 arch/x86/kernel/x86_init.c      |  4 ++--
 arch/x86/mm/mem_encrypt_amd.c   |  8 ++++----
 arch/x86/mm/pat/set_memory.c    |  9 +++++----
 6 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index d11206ceff3b..8897d3cc8a15 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -776,28 +776,30 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 	return true;
 }
 
-static bool tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
-					  bool enc)
+static int tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
+					 bool enc)
 {
 	/*
 	 * Only handle shared->private conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (enc)
-		return tdx_enc_status_changed(vaddr, numpages, enc);
-	return true;
+	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+		return -EIO;
+
+	return 0;
 }
 
-static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
+static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 					 bool enc)
 {
 	/*
 	 * Only handle private->shared conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (!enc)
-		return tdx_enc_status_changed(vaddr, numpages, enc);
-	return true;
+	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+		return -EIO;
+
+	return 0;
 }
 
 void __init tdx_early_init(void)
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index c1088d3661d5..7d2241059d49 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -510,13 +510,12 @@ static int hv_mark_gpa_visibility(u16 count, const u64 pfn[],
  * with host. This function works as wrap of hv_mark_gpa_visibility()
  * with memory base and size.
  */
-static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bool enc)
+static int hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bool enc)
 {
 	enum hv_mem_host_visibility visibility = enc ?
 			VMBUS_PAGE_NOT_VISIBLE : VMBUS_PAGE_VISIBLE_READ_WRITE;
 	u64 *pfn_array;
 	int ret = 0;
-	bool result = true;
 	int i, pfn;
 
 	pfn_array = kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
@@ -530,17 +529,15 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
 		if (pfn == HV_MAX_MODIFY_GPA_REP_COUNT || i == pagecount - 1) {
 			ret = hv_mark_gpa_visibility(pfn, pfn_array,
 						     visibility);
-			if (ret) {
-				result = false;
+			if (ret)
 				goto err_free_pfn_array;
-			}
 			pfn = 0;
 		}
 	}
 
  err_free_pfn_array:
 	kfree(pfn_array);
-	return result;
+	return ret;
 }
 
 static bool hv_vtom_tlb_flush_required(bool private)
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 5240d88db52a..5031cbc6e211 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -150,8 +150,8 @@ struct x86_init_acpi {
  * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
  */
 struct x86_guest {
-	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
-	bool (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
+	int (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
+	int (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_tlb_flush_required)(bool enc);
 	bool (*enc_cache_flush_required)(void);
 };
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index a37ebd3b4773..f0f54e109eb9 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -131,8 +131,8 @@ struct x86_cpuinit_ops x86_cpuinit = {
 
 static void default_nmi_init(void) { };
 
-static bool enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return true; }
-static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return true; }
+static int enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return 0; }
+static int enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return 0; }
 static bool enc_tlb_flush_required_noop(bool enc) { return false; }
 static bool enc_cache_flush_required_noop(void) { return false; }
 static bool is_private_mmio_noop(u64 addr) {return false; }
diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index a68f2dda0948..6cf6cc8ae6a6 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/arch/x86/mm/mem_encrypt_amd.c
@@ -282,7 +282,7 @@ static void enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc)
 #endif
 }
 
-static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
+static int amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
 {
 	/*
 	 * To maintain the security guarantees of SEV-SNP guests, make sure
@@ -291,11 +291,11 @@ static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool
 	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP) && !enc)
 		snp_set_memory_shared(vaddr, npages);
 
-	return true;
+	return 0;
 }
 
 /* Return true unconditionally: return value doesn't matter for the SEV side */
-static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool enc)
+static int amd_enc_status_change_finish(unsigned long vaddr, int npages, bool enc)
 {
 	/*
 	 * After memory is mapped encrypted in the page table, validate it
@@ -307,7 +307,7 @@ static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool e
 	if (!cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
 		enc_dec_hypercall(vaddr, npages << PAGE_SHIFT, enc);
 
-	return true;
+	return 0;
 }
 
 static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bda9f129835e..6fbf22d5fa56 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2152,8 +2152,9 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
 
 	/* Notify hypervisor that we are about to set/clr encryption attribute. */
-	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
-		return -EIO;
+	ret = x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
+	if (ret)
+		return ret;
 
 	ret = __change_page_attr_set_clr(&cpa, 1);
 
@@ -2168,8 +2169,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 
 	/* Notify hypervisor that we have successfully set/clr encryption attribute. */
 	if (!ret) {
-		if (!x86_platform.guest.enc_status_change_finish(addr, numpages, enc))
-			ret = -EIO;
+		ret = x86_platform.guest.enc_status_change_finish(addr,
+								  numpages, enc);
 	}
 
 	return ret;
-- 
2.41.0


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[PATCHv2 06/13] x86/mm: Make x86_platform.guest.enc_status_change_*() return errno

[Kirill A. Shutemov]

TDX is going to have more than one reason to fail
enc_status_change_prepare().

Change the callback to return errno instead of assuming -EIO;
enc_status_change_finish() changed too to keep the interface symmetric.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c         | 20 +++++++++++---------
 arch/x86/hyperv/ivm.c           |  9 +++------
 arch/x86/include/asm/x86_init.h |  4 ++--
 arch/x86/kernel/x86_init.c      |  4 ++--
 arch/x86/mm/mem_encrypt_amd.c   |  8 ++++----
 arch/x86/mm/pat/set_memory.c    |  9 +++++----
 6 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index d11206ceff3b..8897d3cc8a15 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -776,28 +776,30 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 	return true;
 }
 
-static bool tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
-					  bool enc)
+static int tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
+					 bool enc)
 {
 	/*
 	 * Only handle shared->private conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (enc)
-		return tdx_enc_status_changed(vaddr, numpages, enc);
-	return true;
+	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+		return -EIO;
+
+	return 0;
 }
 
-static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
+static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 					 bool enc)
 {
 	/*
 	 * Only handle private->shared conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (!enc)
-		return tdx_enc_status_changed(vaddr, numpages, enc);
-	return true;
+	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+		return -EIO;
+
+	return 0;
 }
 
 void __init tdx_early_init(void)
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index c1088d3661d5..7d2241059d49 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -510,13 +510,12 @@ static int hv_mark_gpa_visibility(u16 count, const u64 pfn[],
  * with host. This function works as wrap of hv_mark_gpa_visibility()
  * with memory base and size.
  */
-static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bool enc)
+static int hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bool enc)
 {
 	enum hv_mem_host_visibility visibility = enc ?
 			VMBUS_PAGE_NOT_VISIBLE : VMBUS_PAGE_VISIBLE_READ_WRITE;
 	u64 *pfn_array;
 	int ret = 0;
-	bool result = true;
 	int i, pfn;
 
 	pfn_array = kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
@@ -530,17 +529,15 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
 		if (pfn == HV_MAX_MODIFY_GPA_REP_COUNT || i == pagecount - 1) {
 			ret = hv_mark_gpa_visibility(pfn, pfn_array,
 						     visibility);
-			if (ret) {
-				result = false;
+			if (ret)
 				goto err_free_pfn_array;
-			}
 			pfn = 0;
 		}
 	}
 
  err_free_pfn_array:
 	kfree(pfn_array);
-	return result;
+	return ret;
 }
 
 static bool hv_vtom_tlb_flush_required(bool private)
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 5240d88db52a..5031cbc6e211 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -150,8 +150,8 @@ struct x86_init_acpi {
  * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
  */
 struct x86_guest {
-	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
-	bool (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
+	int (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
+	int (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_tlb_flush_required)(bool enc);
 	bool (*enc_cache_flush_required)(void);
 };
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index a37ebd3b4773..f0f54e109eb9 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -131,8 +131,8 @@ struct x86_cpuinit_ops x86_cpuinit = {
 
 static void default_nmi_init(void) { };
 
-static bool enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return true; }
-static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return true; }
+static int enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return 0; }
+static int enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return 0; }
 static bool enc_tlb_flush_required_noop(bool enc) { return false; }
 static bool enc_cache_flush_required_noop(void) { return false; }
 static bool is_private_mmio_noop(u64 addr) {return false; }
diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index a68f2dda0948..6cf6cc8ae6a6 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/arch/x86/mm/mem_encrypt_amd.c
@@ -282,7 +282,7 @@ static void enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc)
 #endif
 }
 
-static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
+static int amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
 {
 	/*
 	 * To maintain the security guarantees of SEV-SNP guests, make sure
@@ -291,11 +291,11 @@ static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool
 	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP) && !enc)
 		snp_set_memory_shared(vaddr, npages);
 
-	return true;
+	return 0;
 }
 
 /* Return true unconditionally: return value doesn't matter for the SEV side */
-static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool enc)
+static int amd_enc_status_change_finish(unsigned long vaddr, int npages, bool enc)
 {
 	/*
 	 * After memory is mapped encrypted in the page table, validate it
@@ -307,7 +307,7 @@ static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool e
 	if (!cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
 		enc_dec_hypercall(vaddr, npages << PAGE_SHIFT, enc);
 
-	return true;
+	return 0;
 }
 
 static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bda9f129835e..6fbf22d5fa56 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2152,8 +2152,9 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
 
 	/* Notify hypervisor that we are about to set/clr encryption attribute. */
-	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
-		return -EIO;
+	ret = x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
+	if (ret)
+		return ret;
 
 	ret = __change_page_attr_set_clr(&cpa, 1);
 
@@ -2168,8 +2169,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 
 	/* Notify hypervisor that we have successfully set/clr encryption attribute. */
 	if (!ret) {
-		if (!x86_platform.guest.enc_status_change_finish(addr, numpages, enc))
-			ret = -EIO;
+		ret = x86_platform.guest.enc_status_change_finish(addr,
+								  numpages, enc);
 	}
 
 	return ret;
-- 
2.41.0

[PATCHv2 07/13] x86/mm: Return correct level from lookup_address() if pte is none

[Kirill A. Shutemov]

lookup_address() only returns correct page table level for the entry if
the entry is not none.

Make the helper to always return correct 'level'. It allows to implement
iterator over kernel page tables using lookup_address().

Add one more entry into enum pg_level to indicate size of VA covered by
one PGD entry in 5-level paging mode.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/include/asm/pgtable_types.h | 1 +
 arch/x86/mm/pat/set_memory.c         | 8 ++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 0b748ee16b3d..3f648ffdfbe5 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -548,6 +548,7 @@ enum pg_level {
 	PG_LEVEL_2M,
 	PG_LEVEL_1G,
 	PG_LEVEL_512G,
+	PG_LEVEL_256T,
 	PG_LEVEL_NUM
 };
 
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6fbf22d5fa56..01f827eb8e80 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -666,32 +666,32 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
 	pud_t *pud;
 	pmd_t *pmd;
 
-	*level = PG_LEVEL_NONE;
+	*level = PG_LEVEL_256T;
 
 	if (pgd_none(*pgd))
 		return NULL;
 
+	*level = PG_LEVEL_512G;
 	p4d = p4d_offset(pgd, address);
 	if (p4d_none(*p4d))
 		return NULL;
 
-	*level = PG_LEVEL_512G;
 	if (p4d_large(*p4d) || !p4d_present(*p4d))
 		return (pte_t *)p4d;
 
+	*level = PG_LEVEL_1G;
 	pud = pud_offset(p4d, address);
 	if (pud_none(*pud))
 		return NULL;
 
-	*level = PG_LEVEL_1G;
 	if (pud_large(*pud) || !pud_present(*pud))
 		return (pte_t *)pud;
 
+	*level = PG_LEVEL_2M;
 	pmd = pmd_offset(pud, address);
 	if (pmd_none(*pmd))
 		return NULL;
 
-	*level = PG_LEVEL_2M;
 	if (pmd_large(*pmd) || !pmd_present(*pmd))
 		return (pte_t *)pmd;
 
-- 
2.41.0


_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCHv2 07/13] x86/mm: Return correct level from lookup_address() if pte is none

[Kirill A. Shutemov]

lookup_address() only returns correct page table level for the entry if
the entry is not none.

Make the helper to always return correct 'level'. It allows to implement
iterator over kernel page tables using lookup_address().

Add one more entry into enum pg_level to indicate size of VA covered by
one PGD entry in 5-level paging mode.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/include/asm/pgtable_types.h | 1 +
 arch/x86/mm/pat/set_memory.c         | 8 ++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 0b748ee16b3d..3f648ffdfbe5 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -548,6 +548,7 @@ enum pg_level {
 	PG_LEVEL_2M,
 	PG_LEVEL_1G,
 	PG_LEVEL_512G,
+	PG_LEVEL_256T,
 	PG_LEVEL_NUM
 };
 
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6fbf22d5fa56..01f827eb8e80 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -666,32 +666,32 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
 	pud_t *pud;
 	pmd_t *pmd;
 
-	*level = PG_LEVEL_NONE;
+	*level = PG_LEVEL_256T;
 
 	if (pgd_none(*pgd))
 		return NULL;
 
+	*level = PG_LEVEL_512G;
 	p4d = p4d_offset(pgd, address);
 	if (p4d_none(*p4d))
 		return NULL;
 
-	*level = PG_LEVEL_512G;
 	if (p4d_large(*p4d) || !p4d_present(*p4d))
 		return (pte_t *)p4d;
 
+	*level = PG_LEVEL_1G;
 	pud = pud_offset(p4d, address);
 	if (pud_none(*pud))
 		return NULL;
 
-	*level = PG_LEVEL_1G;
 	if (pud_large(*pud) || !pud_present(*pud))
 		return (pte_t *)pud;
 
+	*level = PG_LEVEL_2M;
 	pmd = pmd_offset(pud, address);
 	if (pmd_none(*pmd))
 		return NULL;
 
-	*level = PG_LEVEL_2M;
 	if (pmd_large(*pmd) || !pmd_present(*pmd))
 		return (pte_t *)pmd;
 
-- 
2.41.0

[PATCHv2 08/13] x86/tdx: Account shared memory

[Kirill A. Shutemov]

The kernel will convert all shared memory back to private during kexec.
The direct mapping page tables will provide information on which memory
is shared.

It is extremely important to convert all shared memory. If a page is
missed, it will cause the second kernel to crash when it accesses it.

Keep track of the number of shared pages. This will allow for
cross-checking against the shared information in the direct mapping and
reporting if the shared bit is lost.

Include a debugfs interface that allows for the check to be performed at
any point.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c | 69 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 8897d3cc8a15..587bdeb88afa 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -5,6 +5,7 @@
 #define pr_fmt(fmt)     "tdx: " fmt
 
 #include <linux/cpufeature.h>
+#include <linux/debugfs.h>
 #include <linux/export.h>
 #include <linux/io.h>
 #include <asm/coco.h>
@@ -37,6 +38,13 @@
 
 #define TDREPORT_SUBTYPE_0	0
 
+static atomic_long_t nr_shared;
+
+static inline bool pte_decrypted(pte_t pte)
+{
+	return cc_mkdec(pte_val(pte)) == pte_val(pte);
+}
+
 /* Called from __tdx_hypercall() for unrecoverable failure */
 noinstr void __noreturn __tdx_hypercall_failed(void)
 {
@@ -799,6 +807,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
 		return -EIO;
 
+	if (enc)
+		atomic_long_sub(numpages, &nr_shared);
+	else
+		atomic_long_add(numpages, &nr_shared);
+
 	return 0;
 }
 
@@ -874,3 +887,59 @@ void __init tdx_early_init(void)
 
 	pr_info("Guest detected\n");
 }
+
+#ifdef CONFIG_DEBUG_FS
+static int tdx_shared_memory_show(struct seq_file *m, void *p)
+{
+	unsigned long addr, end;
+	unsigned long found = 0;
+
+	addr = PAGE_OFFSET;
+	end  = PAGE_OFFSET + get_max_mapped();
+
+	while (addr < end) {
+		unsigned long size;
+		unsigned int level;
+		pte_t *pte;
+
+		pte = lookup_address(addr, &level);
+		size = page_level_size(level);
+
+		if (pte && pte_decrypted(*pte))
+			found += size / PAGE_SIZE;
+
+		addr += size;
+
+		cond_resched();
+	}
+
+	seq_printf(m, "Number of unshared pages in kernel page tables:  %16lu\n",
+		   found);
+	seq_printf(m, "Number of pages accounted as unshared:           %16ld\n",
+		   atomic_long_read(&nr_shared));
+	return 0;
+}
+
+static int tdx_shared_memory_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, tdx_shared_memory_show, NULL);
+}
+
+static const struct file_operations tdx_shared_memory_fops = {
+	.open           = tdx_shared_memory_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static __init int debug_tdx_shared_memory(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return 0;
+
+	debugfs_create_file("tdx_shared_memory", S_IRUSR, arch_debugfs_dir,
+			    NULL, &tdx_shared_memory_fops);
+	return 0;
+}
+fs_initcall(debug_tdx_shared_memory);
+#endif
-- 
2.41.0

[PATCHv2 08/13] x86/tdx: Account shared memory

[Kirill A. Shutemov]

The kernel will convert all shared memory back to private during kexec.
The direct mapping page tables will provide information on which memory
is shared.

It is extremely important to convert all shared memory. If a page is
missed, it will cause the second kernel to crash when it accesses it.

Keep track of the number of shared pages. This will allow for
cross-checking against the shared information in the direct mapping and
reporting if the shared bit is lost.

Include a debugfs interface that allows for the check to be performed at
any point.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/tdx.c | 69 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 8897d3cc8a15..587bdeb88afa 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -5,6 +5,7 @@
 #define pr_fmt(fmt)     "tdx: " fmt
 
 #include <linux/cpufeature.h>
+#include <linux/debugfs.h>
 #include <linux/export.h>
 #include <linux/io.h>
 #include <asm/coco.h>
@@ -37,6 +38,13 @@
 
 #define TDREPORT_SUBTYPE_0	0
 
+static atomic_long_t nr_shared;
+
+static inline bool pte_decrypted(pte_t pte)
+{
+	return cc_mkdec(pte_val(pte)) == pte_val(pte);
+}
+
 /* Called from __tdx_hypercall() for unrecoverable failure */
 noinstr void __noreturn __tdx_hypercall_failed(void)
 {
@@ -799,6 +807,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
 		return -EIO;
 
+	if (enc)
+		atomic_long_sub(numpages, &nr_shared);
+	else
+		atomic_long_add(numpages, &nr_shared);
+
 	return 0;
 }
 
@@ -874,3 +887,59 @@ void __init tdx_early_init(void)
 
 	pr_info("Guest detected\n");
 }
+
+#ifdef CONFIG_DEBUG_FS
+static int tdx_shared_memory_show(struct seq_file *m, void *p)
+{
+	unsigned long addr, end;
+	unsigned long found = 0;
+
+	addr = PAGE_OFFSET;
+	end  = PAGE_OFFSET + get_max_mapped();
+
+	while (addr < end) {
+		unsigned long size;
+		unsigned int level;
+		pte_t *pte;
+
+		pte = lookup_address(addr, &level);
+		size = page_level_size(level);
+
+		if (pte && pte_decrypted(*pte))
+			found += size / PAGE_SIZE;
+
+		addr += size;
+
+		cond_resched();
+	}
+
+	seq_printf(m, "Number of unshared pages in kernel page tables:  %16lu\n",
+		   found);
+	seq_printf(m, "Number of pages accounted as unshared:           %16ld\n",
+		   atomic_long_read(&nr_shared));
+	return 0;
+}
+
+static int tdx_shared_memory_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, tdx_shared_memory_show, NULL);
+}
+
+static const struct file_operations tdx_shared_memory_fops = {
+	.open           = tdx_shared_memory_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static __init int debug_tdx_shared_memory(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return 0;
+
+	debugfs_create_file("tdx_shared_memory", S_IRUSR, arch_debugfs_dir,
+			    NULL, &tdx_shared_memory_fops);
+	return 0;
+}
+fs_initcall(debug_tdx_shared_memory);
+#endif
-- 
2.41.0


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[PATCHv2 09/13] x86/tdx: Convert shared memory back to private on kexec

[Kirill A. Shutemov]

TDX guests allocate shared buffers to perform I/O. It is done by
allocating pages normally from the buddy allocator and converting them
to shared with set_memory_decrypted().

The second kernel has no idea what memory is converted this way. It only
sees E820_TYPE_RAM.

Accessing shared memory via private mapping is fatal. It leads to
unrecoverable TD exit.

On kexec walk direct mapping and convert all shared memory back to
private. It makes all RAM private again and second kernel may use it
normally.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/kexec.c       |   0
 arch/x86/coco/tdx/tdx.c         | 120 +++++++++++++++++++++++++++++++-
 arch/x86/include/asm/x86_init.h |   1 +
 arch/x86/kernel/crash.c         |   4 ++
 arch/x86/kernel/reboot.c        |   5 ++
 5 files changed, 128 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/coco/tdx/kexec.c

diff --git a/arch/x86/coco/tdx/kexec.c b/arch/x86/coco/tdx/kexec.c
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 587bdeb88afa..2be23fe8cb3d 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -6,14 +6,17 @@
 
 #include <linux/cpufeature.h>
 #include <linux/debugfs.h>
+#include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/io.h>
+#include <linux/kexec.h>
 #include <asm/coco.h>
 #include <asm/tdx.h>
 #include <asm/vmx.h>
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
+#include <asm/set_memory.h>
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -40,6 +43,9 @@
 
 static atomic_long_t nr_shared;
 
+static atomic_t conversions_in_progress;
+static bool conversion_allowed = true;
+
 static inline bool pte_decrypted(pte_t pte)
 {
 	return cc_mkdec(pte_val(pte)) == pte_val(pte);
@@ -704,6 +710,14 @@ static bool tdx_tlb_flush_required(bool private)
 
 static bool tdx_cache_flush_required(void)
 {
+	/*
+	 * Avoid issuing CLFLUSH on set_memory_decrypted() if conversions
+	 * stopped. Otherwise it can race with unshare_all_memory() and trigger
+	 * implicit conversion to shared.
+	 */
+	if (!conversion_allowed)
+		return false;
+
 	/*
 	 * AMD SME/SEV can avoid cache flushing if HW enforces cache coherence.
 	 * TDX doesn't have such capability.
@@ -787,12 +801,25 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 static int tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
 					 bool enc)
 {
+	atomic_inc(&conversions_in_progress);
+
+	/*
+	 * Check after bumping conversions_in_progress to serialize
+	 * against tdx_shutdown().
+	 */
+	if (!conversion_allowed) {
+		atomic_dec(&conversions_in_progress);
+		return -EBUSY;
+	}
+
 	/*
 	 * Only handle shared->private conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc)) {
+		atomic_dec(&conversions_in_progress);
 		return -EIO;
+	}
 
 	return 0;
 }
@@ -804,17 +831,104 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 	 * Only handle private->shared conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc)) {
+		atomic_dec(&conversions_in_progress);
 		return -EIO;
+	}
 
 	if (enc)
 		atomic_long_sub(numpages, &nr_shared);
 	else
 		atomic_long_add(numpages, &nr_shared);
 
+	atomic_dec(&conversions_in_progress);
+
 	return 0;
 }
 
+void tdx_kexec_unshare_mem(bool crash)
+{
+	unsigned long addr, end;
+	long found = 0, shared;
+
+	/* Stop new private<->shared conversions */
+	conversion_allowed = false;
+
+	/*
+	 * Crash kernel reaches here with interrupts disabled: can't wait for
+	 * conversions to finish.
+	 *
+	 * If race happened, just report and proceed.
+	 */
+	if (!crash) {
+		unsigned long timeout;
+
+		/*
+		 * Wait for in-flight conversions to complete.
+		 *
+		 * Do not wait more than 30 seconds.
+		 */
+		timeout = 30 * USEC_PER_SEC;
+		while (atomic_read(&conversions_in_progress) && timeout--)
+			udelay(1);
+	}
+
+	if (atomic_read(&conversions_in_progress))
+		pr_warn("Failed to finish shared<->private conversions\n");
+
+	/*
+	 * Walk direct mapping and convert all shared memory back to private,
+	 */
+
+	addr = PAGE_OFFSET;
+	end  = PAGE_OFFSET + get_max_mapped();
+
+	while (addr < end) {
+		unsigned long size;
+		unsigned int level;
+		pte_t *pte;
+
+		pte = lookup_address(addr, &level);
+		size = page_level_size(level);
+
+		if (pte && pte_decrypted(*pte)) {
+			int pages = size / PAGE_SIZE;
+
+			/*
+			 * Touching memory with shared bit set triggers implicit
+			 * conversion to shared.
+			 *
+			 * Make sure nobody touches the shared range from
+			 * now on.
+			 *
+			 * Bypass unmapping for crash scenario. Unmapping
+			 * requires sleepable context, but in crash case kernel
+			 * hits the code path with interrupts disabled.
+			 * It shouldn't be a problem as all secondary CPUs are
+			 * down and kernel runs with interrupts disabled, so
+			 * there is no room for race.
+			 */
+			if (!crash)
+				set_memory_np(addr, pages);
+
+			if (!tdx_enc_status_changed(addr, pages, true)) {
+				pr_err("Failed to unshare range %#lx-%#lx\n",
+				       addr, addr + size);
+			}
+
+			found += pages;
+		}
+
+		addr += size;
+	}
+
+	shared = atomic_long_read(&nr_shared);
+	if (shared != found) {
+		pr_err("shared page accounting is off\n");
+		pr_err("nr_shared = %ld, nr_found = %ld\n", shared, found);
+	}
+}
+
 void __init tdx_early_init(void)
 {
 	struct tdx_module_args args = {
@@ -874,6 +988,8 @@ void __init tdx_early_init(void)
 	x86_platform.guest.enc_cache_flush_required  = tdx_cache_flush_required;
 	x86_platform.guest.enc_tlb_flush_required    = tdx_tlb_flush_required;
 
+	x86_platform.guest.enc_kexec_unshare_mem     = tdx_kexec_unshare_mem;
+
 	/*
 	 * TDX intercepts the RDMSR to read the X2APIC ID in the parallel
 	 * bringup low level code. That raises #VE which cannot be handled
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 5031cbc6e211..008a34b42057 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -154,6 +154,7 @@ struct x86_guest {
 	int (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_tlb_flush_required)(bool enc);
 	bool (*enc_cache_flush_required)(void);
+	void (*enc_kexec_unshare_mem)(bool crash);
 };
 
 /**
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..1618224775f5 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -40,6 +40,7 @@
 #include <asm/intel_pt.h>
 #include <asm/crash.h>
 #include <asm/cmdline.h>
+#include <asm/tdx.h>
 
 /* Used while preparing memory map entries for second kernel */
 struct crash_memmap_data {
@@ -107,6 +108,9 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 
 	crash_smp_send_stop();
 
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		x86_platform.guest.enc_kexec_unshare_mem(true);
+
 	cpu_emergency_disable_virtualization();
 
 	/*
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 830425e6d38e..9fb302562bfd 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -12,6 +12,7 @@
 #include <linux/delay.h>
 #include <linux/objtool.h>
 #include <linux/pgtable.h>
+#include <linux/kexec.h>
 #include <acpi/reboot.h>
 #include <asm/io.h>
 #include <asm/apic.h>
@@ -31,6 +32,7 @@
 #include <asm/realmode.h>
 #include <asm/x86_init.h>
 #include <asm/efi.h>
+#include <asm/tdx.h>
 
 /*
  * Power off function, if any
@@ -716,6 +718,9 @@ static void native_machine_emergency_restart(void)
 
 void native_machine_shutdown(void)
 {
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && kexec_in_progress)
+		x86_platform.guest.enc_kexec_unshare_mem(false);
+
 	/* Stop the cpus and apics */
 #ifdef CONFIG_X86_IO_APIC
 	/*
-- 
2.41.0


_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCHv2 09/13] x86/tdx: Convert shared memory back to private on kexec

[Kirill A. Shutemov]

TDX guests allocate shared buffers to perform I/O. It is done by
allocating pages normally from the buddy allocator and converting them
to shared with set_memory_decrypted().

The second kernel has no idea what memory is converted this way. It only
sees E820_TYPE_RAM.

Accessing shared memory via private mapping is fatal. It leads to
unrecoverable TD exit.

On kexec walk direct mapping and convert all shared memory back to
private. It makes all RAM private again and second kernel may use it
normally.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/coco/tdx/kexec.c       |   0
 arch/x86/coco/tdx/tdx.c         | 120 +++++++++++++++++++++++++++++++-
 arch/x86/include/asm/x86_init.h |   1 +
 arch/x86/kernel/crash.c         |   4 ++
 arch/x86/kernel/reboot.c        |   5 ++
 5 files changed, 128 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/coco/tdx/kexec.c

diff --git a/arch/x86/coco/tdx/kexec.c b/arch/x86/coco/tdx/kexec.c
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 587bdeb88afa..2be23fe8cb3d 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -6,14 +6,17 @@
 
 #include <linux/cpufeature.h>
 #include <linux/debugfs.h>
+#include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/io.h>
+#include <linux/kexec.h>
 #include <asm/coco.h>
 #include <asm/tdx.h>
 #include <asm/vmx.h>
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
+#include <asm/set_memory.h>
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -40,6 +43,9 @@
 
 static atomic_long_t nr_shared;
 
+static atomic_t conversions_in_progress;
+static bool conversion_allowed = true;
+
 static inline bool pte_decrypted(pte_t pte)
 {
 	return cc_mkdec(pte_val(pte)) == pte_val(pte);
@@ -704,6 +710,14 @@ static bool tdx_tlb_flush_required(bool private)
 
 static bool tdx_cache_flush_required(void)
 {
+	/*
+	 * Avoid issuing CLFLUSH on set_memory_decrypted() if conversions
+	 * stopped. Otherwise it can race with unshare_all_memory() and trigger
+	 * implicit conversion to shared.
+	 */
+	if (!conversion_allowed)
+		return false;
+
 	/*
 	 * AMD SME/SEV can avoid cache flushing if HW enforces cache coherence.
 	 * TDX doesn't have such capability.
@@ -787,12 +801,25 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 static int tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
 					 bool enc)
 {
+	atomic_inc(&conversions_in_progress);
+
+	/*
+	 * Check after bumping conversions_in_progress to serialize
+	 * against tdx_shutdown().
+	 */
+	if (!conversion_allowed) {
+		atomic_dec(&conversions_in_progress);
+		return -EBUSY;
+	}
+
 	/*
 	 * Only handle shared->private conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+	if (enc && !tdx_enc_status_changed(vaddr, numpages, enc)) {
+		atomic_dec(&conversions_in_progress);
 		return -EIO;
+	}
 
 	return 0;
 }
@@ -804,17 +831,104 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
 	 * Only handle private->shared conversion here.
 	 * See the comment in tdx_early_init().
 	 */
-	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc))
+	if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc)) {
+		atomic_dec(&conversions_in_progress);
 		return -EIO;
+	}
 
 	if (enc)
 		atomic_long_sub(numpages, &nr_shared);
 	else
 		atomic_long_add(numpages, &nr_shared);
 
+	atomic_dec(&conversions_in_progress);
+
 	return 0;
 }
 
+void tdx_kexec_unshare_mem(bool crash)
+{
+	unsigned long addr, end;
+	long found = 0, shared;
+
+	/* Stop new private<->shared conversions */
+	conversion_allowed = false;
+
+	/*
+	 * Crash kernel reaches here with interrupts disabled: can't wait for
+	 * conversions to finish.
+	 *
+	 * If race happened, just report and proceed.
+	 */
+	if (!crash) {
+		unsigned long timeout;
+
+		/*
+		 * Wait for in-flight conversions to complete.
+		 *
+		 * Do not wait more than 30 seconds.
+		 */
+		timeout = 30 * USEC_PER_SEC;
+		while (atomic_read(&conversions_in_progress) && timeout--)
+			udelay(1);
+	}
+
+	if (atomic_read(&conversions_in_progress))
+		pr_warn("Failed to finish shared<->private conversions\n");
+
+	/*
+	 * Walk direct mapping and convert all shared memory back to private,
+	 */
+
+	addr = PAGE_OFFSET;
+	end  = PAGE_OFFSET + get_max_mapped();
+
+	while (addr < end) {
+		unsigned long size;
+		unsigned int level;
+		pte_t *pte;
+
+		pte = lookup_address(addr, &level);
+		size = page_level_size(level);
+
+		if (pte && pte_decrypted(*pte)) {
+			int pages = size / PAGE_SIZE;
+
+			/*
+			 * Touching memory with shared bit set triggers implicit
+			 * conversion to shared.
+			 *
+			 * Make sure nobody touches the shared range from
+			 * now on.
+			 *
+			 * Bypass unmapping for crash scenario. Unmapping
+			 * requires sleepable context, but in crash case kernel
+			 * hits the code path with interrupts disabled.
+			 * It shouldn't be a problem as all secondary CPUs are
+			 * down and kernel runs with interrupts disabled, so
+			 * there is no room for race.
+			 */
+			if (!crash)
+				set_memory_np(addr, pages);
+
+			if (!tdx_enc_status_changed(addr, pages, true)) {
+				pr_err("Failed to unshare range %#lx-%#lx\n",
+				       addr, addr + size);
+			}
+
+			found += pages;
+		}
+
+		addr += size;
+	}
+
+	shared = atomic_long_read(&nr_shared);
+	if (shared != found) {
+		pr_err("shared page accounting is off\n");
+		pr_err("nr_shared = %ld, nr_found = %ld\n", shared, found);
+	}
+}
+
 void __init tdx_early_init(void)
 {
 	struct tdx_module_args args = {
@@ -874,6 +988,8 @@ void __init tdx_early_init(void)
 	x86_platform.guest.enc_cache_flush_required  = tdx_cache_flush_required;
 	x86_platform.guest.enc_tlb_flush_required    = tdx_tlb_flush_required;
 
+	x86_platform.guest.enc_kexec_unshare_mem     = tdx_kexec_unshare_mem;
+
 	/*
 	 * TDX intercepts the RDMSR to read the X2APIC ID in the parallel
 	 * bringup low level code. That raises #VE which cannot be handled
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 5031cbc6e211..008a34b42057 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -154,6 +154,7 @@ struct x86_guest {
 	int (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_tlb_flush_required)(bool enc);
 	bool (*enc_cache_flush_required)(void);
+	void (*enc_kexec_unshare_mem)(bool crash);
 };
 
 /**
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..1618224775f5 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -40,6 +40,7 @@
 #include <asm/intel_pt.h>
 #include <asm/crash.h>
 #include <asm/cmdline.h>
+#include <asm/tdx.h>
 
 /* Used while preparing memory map entries for second kernel */
 struct crash_memmap_data {
@@ -107,6 +108,9 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 
 	crash_smp_send_stop();
 
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		x86_platform.guest.enc_kexec_unshare_mem(true);
+
 	cpu_emergency_disable_virtualization();
 
 	/*
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 830425e6d38e..9fb302562bfd 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -12,6 +12,7 @@
 #include <linux/delay.h>
 #include <linux/objtool.h>
 #include <linux/pgtable.h>
+#include <linux/kexec.h>
 #include <acpi/reboot.h>
 #include <asm/io.h>
 #include <asm/apic.h>
@@ -31,6 +32,7 @@
 #include <asm/realmode.h>
 #include <asm/x86_init.h>
 #include <asm/efi.h>
+#include <asm/tdx.h>
 
 /*
  * Power off function, if any
@@ -716,6 +718,9 @@ static void native_machine_emergency_restart(void)
 
 void native_machine_shutdown(void)
 {
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && kexec_in_progress)
+		x86_platform.guest.enc_kexec_unshare_mem(false);
+
 	/* Stop the cpus and apics */
 #ifdef CONFIG_X86_IO_APIC
 	/*
-- 
2.41.0

[PATCHv2 10/13] x86/mm: Make e820_end_ram_pfn() cover E820_TYPE_ACPI ranges

[Kirill A. Shutemov]

e820__end_of_ram_pfn() is used to calculate max_pfn which, among other
things, guides where direct mapping ends. Any memory above max_pfn is
not going to be present in the direct mapping.

e820__end_of_ram_pfn() finds the end of the ram based on the highest
E820_TYPE_RAM range. But it doesn't includes E820_TYPE_ACPI ranges into
calculation.

Despite the name, E820_TYPE_ACPI covers not only ACPI data, but also EFI
tables and might be required by kernel to function properly.

Usually the problem is hidden because there is some E820_TYPE_RAM memory
above E820_TYPE_ACPI. But crashkernel only presents pre-allocated crash
memory as E820_TYPE_RAM on boot. If the preallocated range is small, it
can fit under the last E820_TYPE_ACPI range.

Modify e820__end_of_ram_pfn() and e820__end_of_low_ram_pfn() to cover
E820_TYPE_ACPI memory.

The problem was discovered during debugging kexec for TDX guest. TDX
guest uses E820_TYPE_ACPI to store the unaccepted memory bitmap and pass
it between the kernels on kexec.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/e820.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index fb8cf953380d..99c80680dc9e 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -827,7 +827,7 @@ u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)
 /*
  * Find the highest page frame number we have available
  */
-static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type type)
+static unsigned long __init e820_end_ram_pfn(unsigned long limit_pfn)
 {
 	int i;
 	unsigned long last_pfn = 0;
@@ -838,7 +838,8 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 		unsigned long start_pfn;
 		unsigned long end_pfn;
 
-		if (entry->type != type)
+		if (entry->type != E820_TYPE_RAM &&
+		    entry->type != E820_TYPE_ACPI)
 			continue;
 
 		start_pfn = entry->addr >> PAGE_SHIFT;
@@ -864,12 +865,12 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 
 unsigned long __init e820__end_of_ram_pfn(void)
 {
-	return e820_end_pfn(MAX_ARCH_PFN, E820_TYPE_RAM);
+	return e820_end_ram_pfn(MAX_ARCH_PFN);
 }
 
 unsigned long __init e820__end_of_low_ram_pfn(void)
 {
-	return e820_end_pfn(1UL << (32 - PAGE_SHIFT), E820_TYPE_RAM);
+	return e820_end_ram_pfn(1UL << (32 - PAGE_SHIFT));
 }
 
 static void __init early_panic(char *msg)
-- 
2.41.0


_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCHv2 10/13] x86/mm: Make e820_end_ram_pfn() cover E820_TYPE_ACPI ranges

[Kirill A. Shutemov]

e820__end_of_ram_pfn() is used to calculate max_pfn which, among other
things, guides where direct mapping ends. Any memory above max_pfn is
not going to be present in the direct mapping.

e820__end_of_ram_pfn() finds the end of the ram based on the highest
E820_TYPE_RAM range. But it doesn't includes E820_TYPE_ACPI ranges into
calculation.

Despite the name, E820_TYPE_ACPI covers not only ACPI data, but also EFI
tables and might be required by kernel to function properly.

Usually the problem is hidden because there is some E820_TYPE_RAM memory
above E820_TYPE_ACPI. But crashkernel only presents pre-allocated crash
memory as E820_TYPE_RAM on boot. If the preallocated range is small, it
can fit under the last E820_TYPE_ACPI range.

Modify e820__end_of_ram_pfn() and e820__end_of_low_ram_pfn() to cover
E820_TYPE_ACPI memory.

The problem was discovered during debugging kexec for TDX guest. TDX
guest uses E820_TYPE_ACPI to store the unaccepted memory bitmap and pass
it between the kernels on kexec.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/e820.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index fb8cf953380d..99c80680dc9e 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -827,7 +827,7 @@ u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)
 /*
  * Find the highest page frame number we have available
  */
-static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type type)
+static unsigned long __init e820_end_ram_pfn(unsigned long limit_pfn)
 {
 	int i;
 	unsigned long last_pfn = 0;
@@ -838,7 +838,8 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 		unsigned long start_pfn;
 		unsigned long end_pfn;
 
-		if (entry->type != type)
+		if (entry->type != E820_TYPE_RAM &&
+		    entry->type != E820_TYPE_ACPI)
 			continue;
 
 		start_pfn = entry->addr >> PAGE_SHIFT;
@@ -864,12 +865,12 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 
 unsigned long __init e820__end_of_ram_pfn(void)
 {
-	return e820_end_pfn(MAX_ARCH_PFN, E820_TYPE_RAM);
+	return e820_end_ram_pfn(MAX_ARCH_PFN);
 }
 
 unsigned long __init e820__end_of_low_ram_pfn(void)
 {
-	return e820_end_pfn(1UL << (32 - PAGE_SHIFT), E820_TYPE_RAM);
+	return e820_end_ram_pfn(1UL << (32 - PAGE_SHIFT));
 }
 
 static void __init early_panic(char *msg)
-- 
2.41.0

[PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
kexec: the second kernel won't be able to use more than one CPU.

Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
The acpi_wakeup_cpu() will use it to bring up secondary cpus.

Zero out mailbox address in the ACPI MADT wakeup structure to indicate
that the mailbox is not usable.  This prevents the kexec()-ed kernel
from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
only be able to use the boot CPU.

This is Linux-specific protocol and not reflected in ACPI spec.

Booting the second kernel with signle CPU is enough to cover the most
common case for kexec -- kdump.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 4bc1d5106afd..9bbe829737e7 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
 
 static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
 {
+	if (!acpi_mp_wake_mailbox_paddr) {
+		pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
+		return -EOPNOTSUPP;
+	}
+
 	/*
 	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
 	 *
@@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	cpu_hotplug_disable_offlining();
 
+	/*
+	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
+	 * It limits kexec: the second kernel won't be able to use more than
+	 * one CPU.
+	 *
+	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
+	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
+	 *
+	 * Zero out mailbox address in the ACPI MADT wakeup structure to
+	 * indicate that the mailbox is not usable.  This prevents the
+	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
+	 * makes the kexec()-ed kernel only be able to use the boot CPU.
+	 *
+	 * This is Linux-specific protocol and not reflected in ACPI spec.
+	 */
+	mp_wake->base_address = 0;
+
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
 	return 0;
-- 
2.41.0

[PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Kirill A. Shutemov]

ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
kexec: the second kernel won't be able to use more than one CPU.

Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
The acpi_wakeup_cpu() will use it to bring up secondary cpus.

Zero out mailbox address in the ACPI MADT wakeup structure to indicate
that the mailbox is not usable.  This prevents the kexec()-ed kernel
from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
only be able to use the boot CPU.

This is Linux-specific protocol and not reflected in ACPI spec.

Booting the second kernel with signle CPU is enough to cover the most
common case for kexec -- kdump.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 4bc1d5106afd..9bbe829737e7 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
 
 static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
 {
+	if (!acpi_mp_wake_mailbox_paddr) {
+		pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
+		return -EOPNOTSUPP;
+	}
+
 	/*
 	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
 	 *
@@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	cpu_hotplug_disable_offlining();
 
+	/*
+	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
+	 * It limits kexec: the second kernel won't be able to use more than
+	 * one CPU.
+	 *
+	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
+	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
+	 *
+	 * Zero out mailbox address in the ACPI MADT wakeup structure to
+	 * indicate that the mailbox is not usable.  This prevents the
+	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
+	 * makes the kexec()-ed kernel only be able to use the boot CPU.
+	 *
+	 * This is Linux-specific protocol and not reflected in ACPI spec.
+	 */
+	mp_wake->base_address = 0;
+
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
 	return 0;
-- 
2.41.0


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[PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Kirill A. Shutemov]

To prepare for the addition of support for MADT wakeup structure version
1, it is necessary to provide more appropriate names for the fields in
the structure.

The field 'mailbox_version' renamed as 'version'. This field signifies
the version of the structure and the related protocols, rather than the
version of the mailbox. This field has not been utilized in the code
thus far.

The field 'base_address' renamed as 'mailbox_address' to clarify the
kind of address it represents. In version 1, the structure includes the
reset vector address. Clear and distinct naming helps to prevent any
confusion.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
 include/acpi/actbl2.h              | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 9bbe829737e7..ad170def2367 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	acpi_table_print_madt_entry(&header->common);
 
-	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
+	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
 
 	cpu_hotplug_disable_offlining();
 
@@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 	 *
 	 * This is Linux-specific protocol and not reflected in ACPI spec.
 	 */
-	mp_wake->base_address = 0;
+	mp_wake->mailbox_address = 0;
 
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
index 3751ae69432f..23b4cfb640fc 100644
--- a/include/acpi/actbl2.h
+++ b/include/acpi/actbl2.h
@@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
 
 struct acpi_madt_multiproc_wakeup {
 	struct acpi_subtable_header header;
-	u16 mailbox_version;
+	u16 version;
 	u32 reserved;		/* reserved - must be zero */
-	u64 base_address;
+	u64 mailbox_address;
 };
 
 #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032
-- 
2.41.0

[PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Kirill A. Shutemov]

To prepare for the addition of support for MADT wakeup structure version
1, it is necessary to provide more appropriate names for the fields in
the structure.

The field 'mailbox_version' renamed as 'version'. This field signifies
the version of the structure and the related protocols, rather than the
version of the mailbox. This field has not been utilized in the code
thus far.

The field 'base_address' renamed as 'mailbox_address' to clarify the
kind of address it represents. In version 1, the structure includes the
reset vector address. Clear and distinct naming helps to prevent any
confusion.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
 include/acpi/actbl2.h              | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 9bbe829737e7..ad170def2367 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	acpi_table_print_madt_entry(&header->common);
 
-	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
+	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
 
 	cpu_hotplug_disable_offlining();
 
@@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 	 *
 	 * This is Linux-specific protocol and not reflected in ACPI spec.
 	 */
-	mp_wake->base_address = 0;
+	mp_wake->mailbox_address = 0;
 
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
index 3751ae69432f..23b4cfb640fc 100644
--- a/include/acpi/actbl2.h
+++ b/include/acpi/actbl2.h
@@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
 
 struct acpi_madt_multiproc_wakeup {
 	struct acpi_subtable_header header;
-	u16 mailbox_version;
+	u16 version;
 	u32 reserved;		/* reserved - must be zero */
-	u64 base_address;
+	u64 mailbox_address;
 };
 
 #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032
-- 
2.41.0


_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Kirill A. Shutemov]

MADT Multiprocessor Wakeup structure version 1 brings support of CPU
offlining: BIOS provides a reset vector where the CPU has to jump to
offline itself. The new TEST mailbox command can be used to test the CPU
offlined successfully and BIOS has control over it.

Add CPU offling support for ACPI MADT wakeup method by implementing
custom cpu_die, play_dead and stop_other_cpus SMP operations.

CPU offlining makes possible to hand over secondary CPUs over kexec, not
limiting the second kernel with single CPU.

The change conforms to the approved ACPI spec change proposal. See the
Link.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/all/13356251.uLZWGnKmhe@kreacher
---
 arch/x86/kernel/acpi/Makefile      |   2 +-
 arch/x86/kernel/acpi/boot.c        |   2 +
 arch/x86/kernel/acpi/madt.S        |  24 ++++
 arch/x86/kernel/acpi/madt_wakeup.c | 197 ++++++++++++++++++++++++++---
 include/acpi/actbl2.h              |  15 ++-
 5 files changed, 220 insertions(+), 20 deletions(-)
 create mode 100644 arch/x86/kernel/acpi/madt.S

diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
index 8c7329c88a75..ccb8198dd8d1 100644
--- a/arch/x86/kernel/acpi/Makefile
+++ b/arch/x86/kernel/acpi/Makefile
@@ -4,7 +4,7 @@ obj-$(CONFIG_ACPI)			+= boot.o
 obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
 obj-$(CONFIG_ACPI_APEI)			+= apei.o
 obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
-obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
+obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o madt.o
 
 ifneq ($(CONFIG_ACPI_PROCESSOR),)
 obj-y					+= cstate.o
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 111bd226ad99..d537dbffa697 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -22,6 +22,7 @@
 #include <linux/efi-bgrt.h>
 #include <linux/serial_core.h>
 #include <linux/pgtable.h>
+#include <linux/sched/hotplug.h>
 
 #include <asm/e820/api.h>
 #include <asm/irqdomain.h>
@@ -33,6 +34,7 @@
 #include <asm/smp.h>
 #include <asm/i8259.h>
 #include <asm/setup.h>
+#include <asm/init.h>
 
 #include "sleep.h" /* To include x86_acpi_suspend_lowlevel */
 static int __initdata acpi_force = 0;
diff --git a/arch/x86/kernel/acpi/madt.S b/arch/x86/kernel/acpi/madt.S
new file mode 100644
index 000000000000..a60435cf4a77
--- /dev/null
+++ b/arch/x86/kernel/acpi/madt.S
@@ -0,0 +1,24 @@
+#include <linux/linkage.h>
+#include <asm/nospec-branch.h>
+#include <asm/page_types.h>
+#include <asm/processor-flags.h>
+
+	.text
+	.align PAGE_SIZE
+SYM_FUNC_START(asm_acpi_mp_play_dead)
+	/* Load address of reset vector into RCX to jump when kernel is ready */
+	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
+
+	/* Turn off global entries. Following CR3 write will flush them. */
+	movq	%cr4, %rdx
+	andq	$~(X86_CR4_PGE), %rdx
+	movq	%rdx, %cr4
+
+	/* Switch to identity mapping */
+	movq	acpi_mp_pgd(%rip), %rax
+	movq	%rax, %cr3
+
+	/* Jump to reset vector */
+	ANNOTATE_RETPOLINE_SAFE
+	jmp	*%rcx
+SYM_FUNC_END(asm_acpi_mp_play_dead)
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index ad170def2367..f9ff14ee2892 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -1,8 +1,13 @@
 #include <linux/acpi.h>
 #include <linux/cpu.h>
+#include <linux/delay.h>
 #include <linux/io.h>
+#include <linux/memblock.h>
+#include <linux/pgtable.h>
+#include <linux/sched/hotplug.h>
 #include <asm/apic.h>
 #include <asm/barrier.h>
+#include <asm/init.h>
 #include <asm/processor.h>
 
 /* Physical address of the Multiprocessor Wakeup Structure mailbox */
@@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
 /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
 static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
 
+u64 acpi_mp_pgd;
+u64 acpi_mp_reset_vector_paddr;
+
+void asm_acpi_mp_play_dead(void);
+
+static void __init *alloc_pgt_page(void *context)
+{
+	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+}
+
+/*
+ * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
+ * the same place as in the kernel page tables. The function switches to
+ * the identity mapping and has be present at the same spot in before and
+ * after transition.
+ */
+static int __init init_transition_pgtable(pgd_t *pgd)
+{
+	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
+	unsigned long vaddr, paddr;
+	int result = -ENOMEM;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	vaddr = (unsigned long)asm_acpi_mp_play_dead;
+	pgd += pgd_index(vaddr);
+	if (!pgd_present(*pgd)) {
+		p4d = (p4d_t *)alloc_pgt_page(NULL);
+		if (!p4d)
+			goto err;
+		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
+	}
+	p4d = p4d_offset(pgd, vaddr);
+	if (!p4d_present(*p4d)) {
+		pud = (pud_t *)alloc_pgt_page(NULL);
+		if (!pud)
+			goto err;
+		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
+	}
+	pud = pud_offset(p4d, vaddr);
+	if (!pud_present(*pud)) {
+		pmd = (pmd_t *)alloc_pgt_page(NULL);
+		if (!pmd)
+			goto err;
+		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
+	}
+	pmd = pmd_offset(pud, vaddr);
+	if (!pmd_present(*pmd)) {
+		pte = (pte_t *)alloc_pgt_page(NULL);
+		if (!pte)
+			goto err;
+		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
+	}
+	pte = pte_offset_kernel(pmd, vaddr);
+
+	paddr = __pa(vaddr);
+	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
+
+	return 0;
+err:
+	return result;
+}
+
+static void acpi_mp_play_dead(void)
+{
+	play_dead_common();
+	asm_acpi_mp_play_dead();
+}
+
+static void acpi_mp_cpu_die(unsigned int cpu)
+{
+	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
+	unsigned long timeout;
+
+	/*
+	 * Use TEST mailbox command to prove that BIOS got control over
+	 * the CPU before declaring it dead.
+	 *
+	 * BIOS has to clear 'command' field of the mailbox.
+	 */
+	acpi_mp_wake_mailbox->apic_id = apicid;
+	smp_store_release(&acpi_mp_wake_mailbox->command,
+			  ACPI_MP_WAKE_COMMAND_TEST);
+
+	/* Don't wait longer than a second. */
+	timeout = USEC_PER_SEC;
+	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
+		udelay(1);
+}
+
+static void acpi_mp_stop_other_cpus(int wait)
+{
+	smp_shutdown_nonboot_cpus(smp_processor_id());
+}
+
+static void acpi_mp_crash_stop_other_cpus(void)
+{
+	smp_shutdown_nonboot_cpus(smp_processor_id());
+
+	/* The kernel is broken so disable interrupts */
+	local_irq_disable();
+}
+
+static int __init acpi_mp_setup_reset(u64 reset_vector)
+{
+	pgd_t *pgd;
+	struct x86_mapping_info info = {
+		.alloc_pgt_page = alloc_pgt_page,
+		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
+		.kernpg_flag    = _KERNPG_TABLE_NOENC,
+	};
+
+	pgd = alloc_pgt_page(NULL);
+
+	for (int i = 0; i < nr_pfn_mapped; i++) {
+		unsigned long mstart, mend;
+		mstart = pfn_mapped[i].start << PAGE_SHIFT;
+		mend   = pfn_mapped[i].end << PAGE_SHIFT;
+		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
+			return -ENOMEM;
+	}
+
+	if (kernel_ident_mapping_init(&info, pgd,
+				      PAGE_ALIGN_DOWN(reset_vector),
+				      PAGE_ALIGN(reset_vector + 1))) {
+		return -ENOMEM;
+	}
+
+	if (init_transition_pgtable(pgd))
+		return -ENOMEM;
+
+	smp_ops.play_dead = acpi_mp_play_dead;
+	smp_ops.cpu_die = acpi_mp_cpu_die;
+	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
+	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
+
+	acpi_mp_reset_vector_paddr = reset_vector;
+	acpi_mp_pgd = __pa(pgd);
+
+	return 0;
+}
+
 static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
 {
 	if (!acpi_mp_wake_mailbox_paddr) {
@@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 	struct acpi_madt_multiproc_wakeup *mp_wake;
 
 	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
-	if (BAD_MADT_ENTRY(mp_wake, end))
+	if (!mp_wake)
+		return -EINVAL;
+
+	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
+		return -EINVAL;
+	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
 		return -EINVAL;
 
 	acpi_table_print_madt_entry(&header->common);
 
 	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
 
-	cpu_hotplug_disable_offlining();
+	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
+	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
+		acpi_mp_setup_reset(mp_wake->reset_vector);
+	} else {
+		cpu_hotplug_disable_offlining();
 
-	/*
-	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
-	 * It limits kexec: the second kernel won't be able to use more than
-	 * one CPU.
-	 *
-	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
-	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
-	 *
-	 * Zero out mailbox address in the ACPI MADT wakeup structure to
-	 * indicate that the mailbox is not usable.  This prevents the
-	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
-	 * makes the kexec()-ed kernel only be able to use the boot CPU.
-	 *
-	 * This is Linux-specific protocol and not reflected in ACPI spec.
-	 */
-	mp_wake->mailbox_address = 0;
+		/*
+		 * ACPI MADT doesn't allow to offline CPU after it got woke up.
+		 * It limits kexec: the second kernel won't be able to use more
+		 * than one CPU.
+		 *
+		 * Now acpi_mp_wake_mailbox_paddr already has the mailbox
+		 * address. The acpi_wakeup_cpu() will use it to bring up
+		 * secondary cpus.
+		 *
+		 * Zero out mailbox address in the ACPI MADT wakeup structure
+		 * to indicate that the mailbox is not usable.  This prevents
+		 * the kexec()-ed kernel from reading a vaild mailbox, which in
+		 * turn makes the kexec()-ed kernel only be able to use the boot
+		 * CPU.
+		 *
+		 * This is Linux-specific protocol and not reflected in ACPI spec.
+		 */
+		mp_wake->mailbox_address = 0;
+	}
 
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
index 23b4cfb640fc..8348bf46a648 100644
--- a/include/acpi/actbl2.h
+++ b/include/acpi/actbl2.h
@@ -1112,8 +1112,20 @@ struct acpi_madt_multiproc_wakeup {
 	u16 version;
 	u32 reserved;		/* reserved - must be zero */
 	u64 mailbox_address;
+	u64 reset_vector;
 };
 
+/* Values for Version field above */
+
+enum acpi_madt_multiproc_wakeup_version {
+	ACPI_MADT_MP_WAKEUP_VERSION_NONE = 0,
+	ACPI_MADT_MP_WAKEUP_VERSION_V1 = 1,
+	ACPI_MADT_MP_WAKEUP_VERSION_RESERVED = 2, /* 2 and greater are reserved */
+};
+
+#define ACPI_MADT_MP_WAKEUP_SIZE_V0	16
+#define ACPI_MADT_MP_WAKEUP_SIZE_V1	24
+
 #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032
 #define ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE  2048
 
@@ -1126,7 +1138,8 @@ struct acpi_madt_multiproc_wakeup_mailbox {
 	u8 reserved_firmware[ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE];	/* reserved for firmware use */
 };
 
-#define ACPI_MP_WAKE_COMMAND_WAKEUP    1
+#define ACPI_MP_WAKE_COMMAND_WAKEUP	1
+#define ACPI_MP_WAKE_COMMAND_TEST	2
 
 /* 17: CPU Core Interrupt Controller (ACPI 6.5) */
 
-- 
2.41.0

[PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Kirill A. Shutemov]

MADT Multiprocessor Wakeup structure version 1 brings support of CPU
offlining: BIOS provides a reset vector where the CPU has to jump to
offline itself. The new TEST mailbox command can be used to test the CPU
offlined successfully and BIOS has control over it.

Add CPU offling support for ACPI MADT wakeup method by implementing
custom cpu_die, play_dead and stop_other_cpus SMP operations.

CPU offlining makes possible to hand over secondary CPUs over kexec, not
limiting the second kernel with single CPU.

The change conforms to the approved ACPI spec change proposal. See the
Link.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/all/13356251.uLZWGnKmhe@kreacher
---
 arch/x86/kernel/acpi/Makefile      |   2 +-
 arch/x86/kernel/acpi/boot.c        |   2 +
 arch/x86/kernel/acpi/madt.S        |  24 ++++
 arch/x86/kernel/acpi/madt_wakeup.c | 197 ++++++++++++++++++++++++++---
 include/acpi/actbl2.h              |  15 ++-
 5 files changed, 220 insertions(+), 20 deletions(-)
 create mode 100644 arch/x86/kernel/acpi/madt.S

diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
index 8c7329c88a75..ccb8198dd8d1 100644
--- a/arch/x86/kernel/acpi/Makefile
+++ b/arch/x86/kernel/acpi/Makefile
@@ -4,7 +4,7 @@ obj-$(CONFIG_ACPI)			+= boot.o
 obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
 obj-$(CONFIG_ACPI_APEI)			+= apei.o
 obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
-obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
+obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o madt.o
 
 ifneq ($(CONFIG_ACPI_PROCESSOR),)
 obj-y					+= cstate.o
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 111bd226ad99..d537dbffa697 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -22,6 +22,7 @@
 #include <linux/efi-bgrt.h>
 #include <linux/serial_core.h>
 #include <linux/pgtable.h>
+#include <linux/sched/hotplug.h>
 
 #include <asm/e820/api.h>
 #include <asm/irqdomain.h>
@@ -33,6 +34,7 @@
 #include <asm/smp.h>
 #include <asm/i8259.h>
 #include <asm/setup.h>
+#include <asm/init.h>
 
 #include "sleep.h" /* To include x86_acpi_suspend_lowlevel */
 static int __initdata acpi_force = 0;
diff --git a/arch/x86/kernel/acpi/madt.S b/arch/x86/kernel/acpi/madt.S
new file mode 100644
index 000000000000..a60435cf4a77
--- /dev/null
+++ b/arch/x86/kernel/acpi/madt.S
@@ -0,0 +1,24 @@
+#include <linux/linkage.h>
+#include <asm/nospec-branch.h>
+#include <asm/page_types.h>
+#include <asm/processor-flags.h>
+
+	.text
+	.align PAGE_SIZE
+SYM_FUNC_START(asm_acpi_mp_play_dead)
+	/* Load address of reset vector into RCX to jump when kernel is ready */
+	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
+
+	/* Turn off global entries. Following CR3 write will flush them. */
+	movq	%cr4, %rdx
+	andq	$~(X86_CR4_PGE), %rdx
+	movq	%rdx, %cr4
+
+	/* Switch to identity mapping */
+	movq	acpi_mp_pgd(%rip), %rax
+	movq	%rax, %cr3
+
+	/* Jump to reset vector */
+	ANNOTATE_RETPOLINE_SAFE
+	jmp	*%rcx
+SYM_FUNC_END(asm_acpi_mp_play_dead)
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index ad170def2367..f9ff14ee2892 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -1,8 +1,13 @@
 #include <linux/acpi.h>
 #include <linux/cpu.h>
+#include <linux/delay.h>
 #include <linux/io.h>
+#include <linux/memblock.h>
+#include <linux/pgtable.h>
+#include <linux/sched/hotplug.h>
 #include <asm/apic.h>
 #include <asm/barrier.h>
+#include <asm/init.h>
 #include <asm/processor.h>
 
 /* Physical address of the Multiprocessor Wakeup Structure mailbox */
@@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
 /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
 static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
 
+u64 acpi_mp_pgd;
+u64 acpi_mp_reset_vector_paddr;
+
+void asm_acpi_mp_play_dead(void);
+
+static void __init *alloc_pgt_page(void *context)
+{
+	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+}
+
+/*
+ * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
+ * the same place as in the kernel page tables. The function switches to
+ * the identity mapping and has be present at the same spot in before and
+ * after transition.
+ */
+static int __init init_transition_pgtable(pgd_t *pgd)
+{
+	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
+	unsigned long vaddr, paddr;
+	int result = -ENOMEM;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	vaddr = (unsigned long)asm_acpi_mp_play_dead;
+	pgd += pgd_index(vaddr);
+	if (!pgd_present(*pgd)) {
+		p4d = (p4d_t *)alloc_pgt_page(NULL);
+		if (!p4d)
+			goto err;
+		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
+	}
+	p4d = p4d_offset(pgd, vaddr);
+	if (!p4d_present(*p4d)) {
+		pud = (pud_t *)alloc_pgt_page(NULL);
+		if (!pud)
+			goto err;
+		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
+	}
+	pud = pud_offset(p4d, vaddr);
+	if (!pud_present(*pud)) {
+		pmd = (pmd_t *)alloc_pgt_page(NULL);
+		if (!pmd)
+			goto err;
+		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
+	}
+	pmd = pmd_offset(pud, vaddr);
+	if (!pmd_present(*pmd)) {
+		pte = (pte_t *)alloc_pgt_page(NULL);
+		if (!pte)
+			goto err;
+		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
+	}
+	pte = pte_offset_kernel(pmd, vaddr);
+
+	paddr = __pa(vaddr);
+	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
+
+	return 0;
+err:
+	return result;
+}
+
+static void acpi_mp_play_dead(void)
+{
+	play_dead_common();
+	asm_acpi_mp_play_dead();
+}
+
+static void acpi_mp_cpu_die(unsigned int cpu)
+{
+	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
+	unsigned long timeout;
+
+	/*
+	 * Use TEST mailbox command to prove that BIOS got control over
+	 * the CPU before declaring it dead.
+	 *
+	 * BIOS has to clear 'command' field of the mailbox.
+	 */
+	acpi_mp_wake_mailbox->apic_id = apicid;
+	smp_store_release(&acpi_mp_wake_mailbox->command,
+			  ACPI_MP_WAKE_COMMAND_TEST);
+
+	/* Don't wait longer than a second. */
+	timeout = USEC_PER_SEC;
+	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
+		udelay(1);
+}
+
+static void acpi_mp_stop_other_cpus(int wait)
+{
+	smp_shutdown_nonboot_cpus(smp_processor_id());
+}
+
+static void acpi_mp_crash_stop_other_cpus(void)
+{
+	smp_shutdown_nonboot_cpus(smp_processor_id());
+
+	/* The kernel is broken so disable interrupts */
+	local_irq_disable();
+}
+
+static int __init acpi_mp_setup_reset(u64 reset_vector)
+{
+	pgd_t *pgd;
+	struct x86_mapping_info info = {
+		.alloc_pgt_page = alloc_pgt_page,
+		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
+		.kernpg_flag    = _KERNPG_TABLE_NOENC,
+	};
+
+	pgd = alloc_pgt_page(NULL);
+
+	for (int i = 0; i < nr_pfn_mapped; i++) {
+		unsigned long mstart, mend;
+		mstart = pfn_mapped[i].start << PAGE_SHIFT;
+		mend   = pfn_mapped[i].end << PAGE_SHIFT;
+		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
+			return -ENOMEM;
+	}
+
+	if (kernel_ident_mapping_init(&info, pgd,
+				      PAGE_ALIGN_DOWN(reset_vector),
+				      PAGE_ALIGN(reset_vector + 1))) {
+		return -ENOMEM;
+	}
+
+	if (init_transition_pgtable(pgd))
+		return -ENOMEM;
+
+	smp_ops.play_dead = acpi_mp_play_dead;
+	smp_ops.cpu_die = acpi_mp_cpu_die;
+	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
+	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
+
+	acpi_mp_reset_vector_paddr = reset_vector;
+	acpi_mp_pgd = __pa(pgd);
+
+	return 0;
+}
+
 static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
 {
 	if (!acpi_mp_wake_mailbox_paddr) {
@@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 	struct acpi_madt_multiproc_wakeup *mp_wake;
 
 	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
-	if (BAD_MADT_ENTRY(mp_wake, end))
+	if (!mp_wake)
+		return -EINVAL;
+
+	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
+		return -EINVAL;
+	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
 		return -EINVAL;
 
 	acpi_table_print_madt_entry(&header->common);
 
 	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
 
-	cpu_hotplug_disable_offlining();
+	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
+	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
+		acpi_mp_setup_reset(mp_wake->reset_vector);
+	} else {
+		cpu_hotplug_disable_offlining();
 
-	/*
-	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
-	 * It limits kexec: the second kernel won't be able to use more than
-	 * one CPU.
-	 *
-	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
-	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
-	 *
-	 * Zero out mailbox address in the ACPI MADT wakeup structure to
-	 * indicate that the mailbox is not usable.  This prevents the
-	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
-	 * makes the kexec()-ed kernel only be able to use the boot CPU.
-	 *
-	 * This is Linux-specific protocol and not reflected in ACPI spec.
-	 */
-	mp_wake->mailbox_address = 0;
+		/*
+		 * ACPI MADT doesn't allow to offline CPU after it got woke up.
+		 * It limits kexec: the second kernel won't be able to use more
+		 * than one CPU.
+		 *
+		 * Now acpi_mp_wake_mailbox_paddr already has the mailbox
+		 * address. The acpi_wakeup_cpu() will use it to bring up
+		 * secondary cpus.
+		 *
+		 * Zero out mailbox address in the ACPI MADT wakeup structure
+		 * to indicate that the mailbox is not usable.  This prevents
+		 * the kexec()-ed kernel from reading a vaild mailbox, which in
+		 * turn makes the kexec()-ed kernel only be able to use the boot
+		 * CPU.
+		 *
+		 * This is Linux-specific protocol and not reflected in ACPI spec.
+		 */
+		mp_wake->mailbox_address = 0;
+	}
 
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
index 23b4cfb640fc..8348bf46a648 100644
--- a/include/acpi/actbl2.h
+++ b/include/acpi/actbl2.h
@@ -1112,8 +1112,20 @@ struct acpi_madt_multiproc_wakeup {
 	u16 version;
 	u32 reserved;		/* reserved - must be zero */
 	u64 mailbox_address;
+	u64 reset_vector;
 };
 
+/* Values for Version field above */
+
+enum acpi_madt_multiproc_wakeup_version {
+	ACPI_MADT_MP_WAKEUP_VERSION_NONE = 0,
+	ACPI_MADT_MP_WAKEUP_VERSION_V1 = 1,
+	ACPI_MADT_MP_WAKEUP_VERSION_RESERVED = 2, /* 2 and greater are reserved */
+};
+
+#define ACPI_MADT_MP_WAKEUP_SIZE_V0	16
+#define ACPI_MADT_MP_WAKEUP_SIZE_V1	24
+
 #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032
 #define ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE  2048
 
@@ -1126,7 +1138,8 @@ struct acpi_madt_multiproc_wakeup_mailbox {
 	u8 reserved_firmware[ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE];	/* reserved for firmware use */
 };
 
-#define ACPI_MP_WAKE_COMMAND_WAKEUP    1
+#define ACPI_MP_WAKE_COMMAND_WAKEUP	1
+#define ACPI_MP_WAKE_COMMAND_TEST	2
 
 /* 17: CPU Core Interrupt Controller (ACPI 6.5) */
 
-- 
2.41.0


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Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Fri, Oct 20, 2023, Kirill A. Shutemov wrote:
> kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
> present in the VM. It leads to write to a MSR that doesn't exist on some
> configurations, namely in TDX guest:
> 
> 	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
> 	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)
> 
> kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
> features.
> 
> Do not disable kvmclock if it was not enabled.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Fri, Oct 20, 2023, Kirill A. Shutemov wrote:
> kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
> present in the VM. It leads to write to a MSR that doesn't exist on some
> configurations, namely in TDX guest:
> 
> 	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
> 	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)
> 
> kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
> features.
> 
> Do not disable kvmclock if it was not enabled.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

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Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Vitaly Kuznetsov]

"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:

> kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
> present in the VM. It leads to write to a MSR that doesn't exist on some
> configurations, namely in TDX guest:
>
> 	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
> 	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)
>
> kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
> features.
>
> Do not disable kvmclock if it was not enabled.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kernel/kvmclock.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index fb8f52149be9..f2fff625576d 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -24,8 +24,8 @@
>  
>  static int kvmclock __initdata = 1;
>  static int kvmclock_vsyscall __initdata = 1;
> -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
> -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
> +static int msr_kvm_system_time __ro_after_init;
> +static int msr_kvm_wall_clock __ro_after_init;
>  static u64 kvm_sched_clock_offset __ro_after_init;
>  
>  static int __init parse_no_kvmclock(char *arg)
> @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
>  
>  void kvmclock_disable(void)
>  {
> -	native_write_msr(msr_kvm_system_time, 0, 0);
> +	if (msr_kvm_system_time)
> +		native_write_msr(msr_kvm_system_time, 0, 0);
>  }
>  
>  static void __init kvmclock_init_mem(void)
> @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
>  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
>  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
>  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
> -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
> +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
> +	} else {
>  		return;
>  	}

This should work, so

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

but my personal preference would be to change kvm_guest_cpu_offline()
to check KVM features explicitly instead of checking MSRs against '0'
at least becase it already does so for other features. Completely
untested:

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b8ab9ee5896c..1ee49c98e70a 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
        kvm_pv_disable_apf();
        if (!shutdown)
                apf_task_wake_all();
-       kvmclock_disable();
+       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
+           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
+               kvmclock_disable();
 }

-- 
Vitaly

Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Vitaly Kuznetsov]

"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:

> kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
> present in the VM. It leads to write to a MSR that doesn't exist on some
> configurations, namely in TDX guest:
>
> 	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
> 	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)
>
> kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
> features.
>
> Do not disable kvmclock if it was not enabled.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kernel/kvmclock.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index fb8f52149be9..f2fff625576d 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -24,8 +24,8 @@
>  
>  static int kvmclock __initdata = 1;
>  static int kvmclock_vsyscall __initdata = 1;
> -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
> -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
> +static int msr_kvm_system_time __ro_after_init;
> +static int msr_kvm_wall_clock __ro_after_init;
>  static u64 kvm_sched_clock_offset __ro_after_init;
>  
>  static int __init parse_no_kvmclock(char *arg)
> @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
>  
>  void kvmclock_disable(void)
>  {
> -	native_write_msr(msr_kvm_system_time, 0, 0);
> +	if (msr_kvm_system_time)
> +		native_write_msr(msr_kvm_system_time, 0, 0);
>  }
>  
>  static void __init kvmclock_init_mem(void)
> @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
>  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
>  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
>  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
> -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
> +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
> +	} else {
>  		return;
>  	}

This should work, so

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

but my personal preference would be to change kvm_guest_cpu_offline()
to check KVM features explicitly instead of checking MSRs against '0'
at least becase it already does so for other features. Completely
untested:

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b8ab9ee5896c..1ee49c98e70a 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
        kvm_pv_disable_apf();
        if (!shutdown)
                apf_task_wake_all();
-       kvmclock_disable();
+       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
+           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
+               kvmclock_disable();
 }

-- 
Vitaly


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Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
> > ---
> >  arch/x86/kernel/kvmclock.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index fb8f52149be9..f2fff625576d 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -24,8 +24,8 @@
> >  
> >  static int kvmclock __initdata = 1;
> >  static int kvmclock_vsyscall __initdata = 1;
> > -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
> > -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
> > +static int msr_kvm_system_time __ro_after_init;
> > +static int msr_kvm_wall_clock __ro_after_init;
> >  static u64 kvm_sched_clock_offset __ro_after_init;
> >  
> >  static int __init parse_no_kvmclock(char *arg)
> > @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
> >  
> >  void kvmclock_disable(void)
> >  {
> > -	native_write_msr(msr_kvm_system_time, 0, 0);
> > +	if (msr_kvm_system_time)
> > +		native_write_msr(msr_kvm_system_time, 0, 0);
> >  }
> >  
> >  static void __init kvmclock_init_mem(void)
> > @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
> >  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
> >  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
> >  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
> > -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> > +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> > +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
> > +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
> > +	} else {
> >  		return;
> >  	}
> 
> This should work, so
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> but my personal preference would be to change kvm_guest_cpu_offline()
> to check KVM features explicitly instead of checking MSRs against '0'
> at least becase it already does so for other features. Completely
> untested:
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index b8ab9ee5896c..1ee49c98e70a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
>         kvm_pv_disable_apf();
>         if (!shutdown)
>                 apf_task_wake_all();
> -       kvmclock_disable();
> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
> +               kvmclock_disable();
>  }

That would result in an unnecessray WRMSR in the case where kvmclock is disabled
on the command line.  It _should_ be benign given how the code is written, but
it's not impossible to imagine a scenario where someone disabled kvmclock in the
guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
kvmclock_disable().

Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
> > ---
> >  arch/x86/kernel/kvmclock.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index fb8f52149be9..f2fff625576d 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -24,8 +24,8 @@
> >  
> >  static int kvmclock __initdata = 1;
> >  static int kvmclock_vsyscall __initdata = 1;
> > -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
> > -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
> > +static int msr_kvm_system_time __ro_after_init;
> > +static int msr_kvm_wall_clock __ro_after_init;
> >  static u64 kvm_sched_clock_offset __ro_after_init;
> >  
> >  static int __init parse_no_kvmclock(char *arg)
> > @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
> >  
> >  void kvmclock_disable(void)
> >  {
> > -	native_write_msr(msr_kvm_system_time, 0, 0);
> > +	if (msr_kvm_system_time)
> > +		native_write_msr(msr_kvm_system_time, 0, 0);
> >  }
> >  
> >  static void __init kvmclock_init_mem(void)
> > @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
> >  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
> >  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
> >  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
> > -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> > +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
> > +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
> > +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
> > +	} else {
> >  		return;
> >  	}
> 
> This should work, so
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> but my personal preference would be to change kvm_guest_cpu_offline()
> to check KVM features explicitly instead of checking MSRs against '0'
> at least becase it already does so for other features. Completely
> untested:
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index b8ab9ee5896c..1ee49c98e70a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
>         kvm_pv_disable_apf();
>         if (!shutdown)
>                 apf_task_wake_all();
> -       kvmclock_disable();
> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
> +               kvmclock_disable();
>  }

That would result in an unnecessray WRMSR in the case where kvmclock is disabled
on the command line.  It _should_ be benign given how the code is written, but
it's not impossible to imagine a scenario where someone disabled kvmclock in the
guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
kvmclock_disable().

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Re: [PATCHv2 01/13] x86/acpi: Extract ACPI MADT wakeup code into a separate file

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> In order to prepare for the expansion of support for the ACPI MADT
> wakeup method, move the relevant code into a separate file.
> 
> Introduce a new configuration option to clearly indicate dependencies
> without the use of ifdefs.
> 
> There have been no functional changes.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>


>  arch/x86/Kconfig                   |  7 +++
>  arch/x86/include/asm/acpi.h        |  5 ++
>  arch/x86/kernel/acpi/Makefile      | 11 ++--
>  arch/x86/kernel/acpi/boot.c        | 86 +-----------------------------
>  arch/x86/kernel/acpi/madt_wakeup.c | 81 ++++++++++++++++++++++++++++
>  5 files changed, 100 insertions(+), 90 deletions(-)
>  create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 799102f4d909..9957a73bb386 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1108,6 +1108,13 @@ config X86_LOCAL_APIC
>  	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
>  	select IRQ_DOMAIN_HIERARCHY
>  
> +config X86_ACPI_MADT_WAKEUP
> +	def_bool y
> +	depends on X86_64
> +	depends on ACPI
> +	depends on SMP
> +	depends on X86_LOCAL_APIC
> +
>  config X86_IO_APIC
>  	def_bool y
>  	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index c8a7fc23f63c..b536b5a6a57b 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -73,6 +73,11 @@ static inline bool acpi_skip_set_wakeup_address(void)
>  
>  #define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
>  
> +union acpi_subtable_headers;
> +
> +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +			      const unsigned long end);
> +
>  /*
>   * Check if the CPU can handle C2 and deeper
>   */
> diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
> index fc17b3f136fe..8c7329c88a75 100644
> --- a/arch/x86/kernel/acpi/Makefile
> +++ b/arch/x86/kernel/acpi/Makefile
> @@ -1,11 +1,12 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -obj-$(CONFIG_ACPI)		+= boot.o
> -obj-$(CONFIG_ACPI_SLEEP)	+= sleep.o wakeup_$(BITS).o
> -obj-$(CONFIG_ACPI_APEI)		+= apei.o
> -obj-$(CONFIG_ACPI_CPPC_LIB)	+= cppc.o
> +obj-$(CONFIG_ACPI)			+= boot.o
> +obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
> +obj-$(CONFIG_ACPI_APEI)			+= apei.o
> +obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
> +obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
>  
>  ifneq ($(CONFIG_ACPI_PROCESSOR),)
> -obj-y				+= cstate.o
> +obj-y					+= cstate.o
>  endif
>  
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 2a0ea38955df..111bd226ad99 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -66,13 +66,6 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
>  static bool acpi_support_online_capable;
>  #endif
>  
> -#ifdef CONFIG_X86_64
> -/* Physical address of the Multiprocessor Wakeup Structure mailbox */
> -static u64 acpi_mp_wake_mailbox_paddr;
> -/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> -static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> -#endif
> -
>  #ifdef CONFIG_X86_IO_APIC
>  /*
>   * Locks related to IOAPIC hotplug
> @@ -357,60 +350,6 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
>  
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> -{
> -	/*
> -	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> -	 *
> -	 * Wakeup of secondary CPUs is fully serialized in the core code.
> -	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
> -	 */
> -	if (!acpi_mp_wake_mailbox) {
> -		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> -						sizeof(*acpi_mp_wake_mailbox),
> -						MEMREMAP_WB);
> -	}
> -
> -	/*
> -	 * Mailbox memory is shared between the firmware and OS. Firmware will
> -	 * listen on mailbox command address, and once it receives the wakeup
> -	 * command, the CPU associated with the given apicid will be booted.
> -	 *
> -	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
> -	 * firmware before the wakeup command is visible.  smp_store_release()
> -	 * ensures ordering and visibility.
> -	 */
> -	acpi_mp_wake_mailbox->apic_id	    = apicid;
> -	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
> -	smp_store_release(&acpi_mp_wake_mailbox->command,
> -			  ACPI_MP_WAKE_COMMAND_WAKEUP);
> -
> -	/*
> -	 * Wait for the CPU to wake up.
> -	 *
> -	 * The CPU being woken up is essentially in a spin loop waiting to be
> -	 * woken up. It should not take long for it wake up and acknowledge by
> -	 * zeroing out ->command.
> -	 *
> -	 * ACPI specification doesn't provide any guidance on how long kernel
> -	 * has to wait for a wake up acknowledgement. It also doesn't provide
> -	 * a way to cancel a wake up request if it takes too long.
> -	 *
> -	 * In TDX environment, the VMM has control over how long it takes to
> -	 * wake up secondary. It can postpone scheduling secondary vCPU
> -	 * indefinitely. Giving up on wake up request and reporting error opens
> -	 * possible attack vector for VMM: it can wake up a secondary CPU when
> -	 * kernel doesn't expect it. Wait until positive result of the wake up
> -	 * request.
> -	 */
> -	while (READ_ONCE(acpi_mp_wake_mailbox->command))
> -		cpu_relax();
> -
> -	return 0;
> -}
> -#endif /* CONFIG_X86_64 */
>  #endif /* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef CONFIG_X86_IO_APIC
> @@ -1160,29 +1099,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
>  	}
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> -				     const unsigned long end)
> -{
> -	struct acpi_madt_multiproc_wakeup *mp_wake;
> -
> -	if (!IS_ENABLED(CONFIG_SMP))
> -		return -ENODEV;
> -
> -	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> -		return -EINVAL;
> -
> -	acpi_table_print_madt_entry(&header->common);
> -
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> -
> -	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> -
> -	return 0;
> -}
> -#endif				/* CONFIG_X86_64 */
>  #endif				/* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef	CONFIG_X86_IO_APIC
> @@ -1379,7 +1295,7 @@ static void __init acpi_process_madt(void)
>  				smp_found_config = 1;
>  			}
>  
> -#ifdef CONFIG_X86_64
> +#ifdef CONFIG_X86_ACPI_MADT_WAKEUP
>  			/*
>  			 * Parse MADT MP Wake entry.
>  			 */
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> new file mode 100644
> index 000000000000..58cdfc0b6c0a
> --- /dev/null
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -0,0 +1,81 @@
> +#include <linux/acpi.h>
> +#include <linux/io.h>
> +#include <asm/apic.h>
> +#include <asm/barrier.h>
> +#include <asm/processor.h>
> +
> +/* Physical address of the Multiprocessor Wakeup Structure mailbox */
> +static u64 acpi_mp_wake_mailbox_paddr;
> +
> +/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> +static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> +
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> +	/*
> +	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> +	 *
> +	 * Wakeup of secondary CPUs is fully serialized in the core code.
> +	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
> +	 */
> +	if (!acpi_mp_wake_mailbox) {
> +		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> +						sizeof(*acpi_mp_wake_mailbox),
> +						MEMREMAP_WB);
> +	}
> +
> +	/*
> +	 * Mailbox memory is shared between the firmware and OS. Firmware will
> +	 * listen on mailbox command address, and once it receives the wakeup
> +	 * command, the CPU associated with the given apicid will be booted.
> +	 *
> +	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
> +	 * firmware before the wakeup command is visible.  smp_store_release()
> +	 * ensures ordering and visibility.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id	    = apicid;
> +	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_WAKEUP);
> +
> +	/*
> +	 * Wait for the CPU to wake up.
> +	 *
> +	 * The CPU being woken up is essentially in a spin loop waiting to be
> +	 * woken up. It should not take long for it wake up and acknowledge by
> +	 * zeroing out ->command.
> +	 *
> +	 * ACPI specification doesn't provide any guidance on how long kernel
> +	 * has to wait for a wake up acknowledgement. It also doesn't provide
> +	 * a way to cancel a wake up request if it takes too long.
> +	 *
> +	 * In TDX environment, the VMM has control over how long it takes to
> +	 * wake up secondary. It can postpone scheduling secondary vCPU
> +	 * indefinitely. Giving up on wake up request and reporting error opens
> +	 * possible attack vector for VMM: it can wake up a secondary CPU when
> +	 * kernel doesn't expect it. Wait until positive result of the wake up
> +	 * request.
> +	 */
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command))
> +		cpu_relax();
> +
> +	return 0;
> +}
> +
> +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +			      const unsigned long end)
> +{
> +	struct acpi_madt_multiproc_wakeup *mp_wake;
> +
> +	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> +	if (BAD_MADT_ENTRY(mp_wake, end))
> +		return -EINVAL;
> +
> +	acpi_table_print_madt_entry(&header->common);
> +
> +	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +
> +	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> +
> +	return 0;
> +}

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

Re: [PATCHv2 01/13] x86/acpi: Extract ACPI MADT wakeup code into a separate file

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> In order to prepare for the expansion of support for the ACPI MADT
> wakeup method, move the relevant code into a separate file.
> 
> Introduce a new configuration option to clearly indicate dependencies
> without the use of ifdefs.
> 
> There have been no functional changes.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>


>  arch/x86/Kconfig                   |  7 +++
>  arch/x86/include/asm/acpi.h        |  5 ++
>  arch/x86/kernel/acpi/Makefile      | 11 ++--
>  arch/x86/kernel/acpi/boot.c        | 86 +-----------------------------
>  arch/x86/kernel/acpi/madt_wakeup.c | 81 ++++++++++++++++++++++++++++
>  5 files changed, 100 insertions(+), 90 deletions(-)
>  create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 799102f4d909..9957a73bb386 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1108,6 +1108,13 @@ config X86_LOCAL_APIC
>  	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
>  	select IRQ_DOMAIN_HIERARCHY
>  
> +config X86_ACPI_MADT_WAKEUP
> +	def_bool y
> +	depends on X86_64
> +	depends on ACPI
> +	depends on SMP
> +	depends on X86_LOCAL_APIC
> +
>  config X86_IO_APIC
>  	def_bool y
>  	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index c8a7fc23f63c..b536b5a6a57b 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -73,6 +73,11 @@ static inline bool acpi_skip_set_wakeup_address(void)
>  
>  #define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
>  
> +union acpi_subtable_headers;
> +
> +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +			      const unsigned long end);
> +
>  /*
>   * Check if the CPU can handle C2 and deeper
>   */
> diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
> index fc17b3f136fe..8c7329c88a75 100644
> --- a/arch/x86/kernel/acpi/Makefile
> +++ b/arch/x86/kernel/acpi/Makefile
> @@ -1,11 +1,12 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -obj-$(CONFIG_ACPI)		+= boot.o
> -obj-$(CONFIG_ACPI_SLEEP)	+= sleep.o wakeup_$(BITS).o
> -obj-$(CONFIG_ACPI_APEI)		+= apei.o
> -obj-$(CONFIG_ACPI_CPPC_LIB)	+= cppc.o
> +obj-$(CONFIG_ACPI)			+= boot.o
> +obj-$(CONFIG_ACPI_SLEEP)		+= sleep.o wakeup_$(BITS).o
> +obj-$(CONFIG_ACPI_APEI)			+= apei.o
> +obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
> +obj-$(CONFIG_X86_ACPI_MADT_WAKEUP)	+= madt_wakeup.o
>  
>  ifneq ($(CONFIG_ACPI_PROCESSOR),)
> -obj-y				+= cstate.o
> +obj-y					+= cstate.o
>  endif
>  
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 2a0ea38955df..111bd226ad99 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -66,13 +66,6 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
>  static bool acpi_support_online_capable;
>  #endif
>  
> -#ifdef CONFIG_X86_64
> -/* Physical address of the Multiprocessor Wakeup Structure mailbox */
> -static u64 acpi_mp_wake_mailbox_paddr;
> -/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> -static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> -#endif
> -
>  #ifdef CONFIG_X86_IO_APIC
>  /*
>   * Locks related to IOAPIC hotplug
> @@ -357,60 +350,6 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
>  
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> -{
> -	/*
> -	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> -	 *
> -	 * Wakeup of secondary CPUs is fully serialized in the core code.
> -	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
> -	 */
> -	if (!acpi_mp_wake_mailbox) {
> -		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> -						sizeof(*acpi_mp_wake_mailbox),
> -						MEMREMAP_WB);
> -	}
> -
> -	/*
> -	 * Mailbox memory is shared between the firmware and OS. Firmware will
> -	 * listen on mailbox command address, and once it receives the wakeup
> -	 * command, the CPU associated with the given apicid will be booted.
> -	 *
> -	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
> -	 * firmware before the wakeup command is visible.  smp_store_release()
> -	 * ensures ordering and visibility.
> -	 */
> -	acpi_mp_wake_mailbox->apic_id	    = apicid;
> -	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
> -	smp_store_release(&acpi_mp_wake_mailbox->command,
> -			  ACPI_MP_WAKE_COMMAND_WAKEUP);
> -
> -	/*
> -	 * Wait for the CPU to wake up.
> -	 *
> -	 * The CPU being woken up is essentially in a spin loop waiting to be
> -	 * woken up. It should not take long for it wake up and acknowledge by
> -	 * zeroing out ->command.
> -	 *
> -	 * ACPI specification doesn't provide any guidance on how long kernel
> -	 * has to wait for a wake up acknowledgement. It also doesn't provide
> -	 * a way to cancel a wake up request if it takes too long.
> -	 *
> -	 * In TDX environment, the VMM has control over how long it takes to
> -	 * wake up secondary. It can postpone scheduling secondary vCPU
> -	 * indefinitely. Giving up on wake up request and reporting error opens
> -	 * possible attack vector for VMM: it can wake up a secondary CPU when
> -	 * kernel doesn't expect it. Wait until positive result of the wake up
> -	 * request.
> -	 */
> -	while (READ_ONCE(acpi_mp_wake_mailbox->command))
> -		cpu_relax();
> -
> -	return 0;
> -}
> -#endif /* CONFIG_X86_64 */
>  #endif /* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef CONFIG_X86_IO_APIC
> @@ -1160,29 +1099,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
>  	}
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> -				     const unsigned long end)
> -{
> -	struct acpi_madt_multiproc_wakeup *mp_wake;
> -
> -	if (!IS_ENABLED(CONFIG_SMP))
> -		return -ENODEV;
> -
> -	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> -		return -EINVAL;
> -
> -	acpi_table_print_madt_entry(&header->common);
> -
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> -
> -	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> -
> -	return 0;
> -}
> -#endif				/* CONFIG_X86_64 */
>  #endif				/* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef	CONFIG_X86_IO_APIC
> @@ -1379,7 +1295,7 @@ static void __init acpi_process_madt(void)
>  				smp_found_config = 1;
>  			}
>  
> -#ifdef CONFIG_X86_64
> +#ifdef CONFIG_X86_ACPI_MADT_WAKEUP
>  			/*
>  			 * Parse MADT MP Wake entry.
>  			 */
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> new file mode 100644
> index 000000000000..58cdfc0b6c0a
> --- /dev/null
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -0,0 +1,81 @@
> +#include <linux/acpi.h>
> +#include <linux/io.h>
> +#include <asm/apic.h>
> +#include <asm/barrier.h>
> +#include <asm/processor.h>
> +
> +/* Physical address of the Multiprocessor Wakeup Structure mailbox */
> +static u64 acpi_mp_wake_mailbox_paddr;
> +
> +/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> +static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> +
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> +	/*
> +	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> +	 *
> +	 * Wakeup of secondary CPUs is fully serialized in the core code.
> +	 * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
> +	 */
> +	if (!acpi_mp_wake_mailbox) {
> +		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> +						sizeof(*acpi_mp_wake_mailbox),
> +						MEMREMAP_WB);
> +	}
> +
> +	/*
> +	 * Mailbox memory is shared between the firmware and OS. Firmware will
> +	 * listen on mailbox command address, and once it receives the wakeup
> +	 * command, the CPU associated with the given apicid will be booted.
> +	 *
> +	 * The value of 'apic_id' and 'wakeup_vector' must be visible to the
> +	 * firmware before the wakeup command is visible.  smp_store_release()
> +	 * ensures ordering and visibility.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id	    = apicid;
> +	acpi_mp_wake_mailbox->wakeup_vector = start_ip;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_WAKEUP);
> +
> +	/*
> +	 * Wait for the CPU to wake up.
> +	 *
> +	 * The CPU being woken up is essentially in a spin loop waiting to be
> +	 * woken up. It should not take long for it wake up and acknowledge by
> +	 * zeroing out ->command.
> +	 *
> +	 * ACPI specification doesn't provide any guidance on how long kernel
> +	 * has to wait for a wake up acknowledgement. It also doesn't provide
> +	 * a way to cancel a wake up request if it takes too long.
> +	 *
> +	 * In TDX environment, the VMM has control over how long it takes to
> +	 * wake up secondary. It can postpone scheduling secondary vCPU
> +	 * indefinitely. Giving up on wake up request and reporting error opens
> +	 * possible attack vector for VMM: it can wake up a secondary CPU when
> +	 * kernel doesn't expect it. Wait until positive result of the wake up
> +	 * request.
> +	 */
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command))
> +		cpu_relax();
> +
> +	return 0;
> +}
> +
> +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +			      const unsigned long end)
> +{
> +	struct acpi_madt_multiproc_wakeup *mp_wake;
> +
> +	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> +	if (BAD_MADT_ENTRY(mp_wake, end))
> +		return -EINVAL;
> +
> +	acpi_table_print_madt_entry(&header->common);
> +
> +	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +
> +	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> +
> +	return 0;
> +}

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Vitaly Kuznetsov]

Sean Christopherson <seanjc@google.com> writes:

> On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
>> > ---
>> >  arch/x86/kernel/kvmclock.c | 12 ++++++++----
>> >  1 file changed, 8 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
>> > index fb8f52149be9..f2fff625576d 100644
>> > --- a/arch/x86/kernel/kvmclock.c
>> > +++ b/arch/x86/kernel/kvmclock.c
>> > @@ -24,8 +24,8 @@
>> >  
>> >  static int kvmclock __initdata = 1;
>> >  static int kvmclock_vsyscall __initdata = 1;
>> > -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
>> > -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
>> > +static int msr_kvm_system_time __ro_after_init;
>> > +static int msr_kvm_wall_clock __ro_after_init;
>> >  static u64 kvm_sched_clock_offset __ro_after_init;
>> >  
>> >  static int __init parse_no_kvmclock(char *arg)
>> > @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
>> >  
>> >  void kvmclock_disable(void)
>> >  {
>> > -	native_write_msr(msr_kvm_system_time, 0, 0);
>> > +	if (msr_kvm_system_time)
>> > +		native_write_msr(msr_kvm_system_time, 0, 0);
>> >  }
>> >  
>> >  static void __init kvmclock_init_mem(void)
>> > @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
>> >  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
>> >  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
>> >  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
>> > -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
>> > +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
>> > +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
>> > +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
>> > +	} else {
>> >  		return;
>> >  	}
>> 
>> This should work, so
>> 
>> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> 
>> but my personal preference would be to change kvm_guest_cpu_offline()
>> to check KVM features explicitly instead of checking MSRs against '0'
>> at least becase it already does so for other features. Completely
>> untested:
>> 
>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>> index b8ab9ee5896c..1ee49c98e70a 100644
>> --- a/arch/x86/kernel/kvm.c
>> +++ b/arch/x86/kernel/kvm.c
>> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
>>         kvm_pv_disable_apf();
>>         if (!shutdown)
>>                 apf_task_wake_all();
>> -       kvmclock_disable();
>> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
>> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
>> +               kvmclock_disable();
>>  }
>
> That would result in an unnecessray WRMSR in the case where kvmclock is disabled
> on the command line.  It _should_ be benign given how the code is written, but
> it's not impossible to imagine a scenario where someone disabled kvmclock in the
> guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
> MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
> kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
> kvmclock_disable().

True but we don't have such module params to disable other PV features so
e.g. KVM_FEATURE_PV_EOI/KVM_FEATURE_MIGRATION_CONTROL are written to
unconditionally. Wouldn't it be better to handle parameters like
'no-kvmclock' by clearing the feature bit in kvm_arch_para_features()'s
return value so all kvm_para_has_feature() calls for it just return
'false'? We can even do an umbreall "no-kvm-features=<mask>" to cover
all possible debug cases.

-- 
Vitaly

Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Vitaly Kuznetsov]

Sean Christopherson <seanjc@google.com> writes:

> On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
>> > ---
>> >  arch/x86/kernel/kvmclock.c | 12 ++++++++----
>> >  1 file changed, 8 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
>> > index fb8f52149be9..f2fff625576d 100644
>> > --- a/arch/x86/kernel/kvmclock.c
>> > +++ b/arch/x86/kernel/kvmclock.c
>> > @@ -24,8 +24,8 @@
>> >  
>> >  static int kvmclock __initdata = 1;
>> >  static int kvmclock_vsyscall __initdata = 1;
>> > -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
>> > -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
>> > +static int msr_kvm_system_time __ro_after_init;
>> > +static int msr_kvm_wall_clock __ro_after_init;
>> >  static u64 kvm_sched_clock_offset __ro_after_init;
>> >  
>> >  static int __init parse_no_kvmclock(char *arg)
>> > @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void)
>> >  
>> >  void kvmclock_disable(void)
>> >  {
>> > -	native_write_msr(msr_kvm_system_time, 0, 0);
>> > +	if (msr_kvm_system_time)
>> > +		native_write_msr(msr_kvm_system_time, 0, 0);
>> >  }
>> >  
>> >  static void __init kvmclock_init_mem(void)
>> > @@ -294,7 +295,10 @@ void __init kvmclock_init(void)
>> >  	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
>> >  		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
>> >  		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
>> > -	} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
>> > +	} else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
>> > +		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
>> > +		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
>> > +	} else {
>> >  		return;
>> >  	}
>> 
>> This should work, so
>> 
>> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> 
>> but my personal preference would be to change kvm_guest_cpu_offline()
>> to check KVM features explicitly instead of checking MSRs against '0'
>> at least becase it already does so for other features. Completely
>> untested:
>> 
>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>> index b8ab9ee5896c..1ee49c98e70a 100644
>> --- a/arch/x86/kernel/kvm.c
>> +++ b/arch/x86/kernel/kvm.c
>> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
>>         kvm_pv_disable_apf();
>>         if (!shutdown)
>>                 apf_task_wake_all();
>> -       kvmclock_disable();
>> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
>> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
>> +               kvmclock_disable();
>>  }
>
> That would result in an unnecessray WRMSR in the case where kvmclock is disabled
> on the command line.  It _should_ be benign given how the code is written, but
> it's not impossible to imagine a scenario where someone disabled kvmclock in the
> guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
> MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
> kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
> kvmclock_disable().

True but we don't have such module params to disable other PV features so
e.g. KVM_FEATURE_PV_EOI/KVM_FEATURE_MIGRATION_CONTROL are written to
unconditionally. Wouldn't it be better to handle parameters like
'no-kvmclock' by clearing the feature bit in kvm_arch_para_features()'s
return value so all kvm_para_has_feature() calls for it just return
'false'? We can even do an umbreall "no-kvm-features=<mask>" to cover
all possible debug cases.

-- 
Vitaly


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Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> Currently offlining hotplug prevented based on the confidential
> computing attribute which is set for Intel TDX. But TDX is not
> the only possible user of the wake up method.
> 
> Introduce cpu_hotplug_not_supported() that can be called to indicate
> that CPU offlining should be disabled.
> 
> This function is going to replace CC_ATTR_HOTPLUG_DISABLED for ACPI
> MADT.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  include/linux/cpu.h |  2 ++
>  kernel/cpu.c        | 13 ++++++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index f19f56501809..97832ced939d 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -132,6 +132,7 @@ extern void cpus_read_lock(void);
>  extern void cpus_read_unlock(void);
>  extern int  cpus_read_trylock(void);
>  extern void lockdep_assert_cpus_held(void);
> +extern void cpu_hotplug_disable_offlining(void);
>  extern void cpu_hotplug_disable(void);
>  extern void cpu_hotplug_enable(void);
>  void clear_tasks_mm_cpumask(int cpu);
> @@ -147,6 +148,7 @@ static inline void cpus_read_lock(void) { }
>  static inline void cpus_read_unlock(void) { }
>  static inline int  cpus_read_trylock(void) { return true; }
>  static inline void lockdep_assert_cpus_held(void) { }
> +static inline void cpu_hotplug_disable_offlining(void) { }
>  static inline void cpu_hotplug_disable(void) { }
>  static inline void cpu_hotplug_enable(void) { }
>  static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6de7c6bb74ee..faebee0050a2 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -484,6 +484,8 @@ static int cpu_hotplug_disabled;
>  
>  DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
>  
> +static bool cpu_hotplug_offline_disabled;
> +
>  void cpus_read_lock(void)
>  {
>  	percpu_down_read(&cpu_hotplug_lock);
> @@ -543,6 +545,14 @@ static void lockdep_release_cpus_lock(void)
>  	rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
>  }
>  
> +/* Declare CPU offlining not supported */
> +void cpu_hotplug_disable_offlining(void)
> +{
> +	cpu_maps_update_begin();
> +	cpu_hotplug_offline_disabled = true;
> +	cpu_maps_update_done();
> +}
> +
>  /*
>   * Wait for currently running CPU hotplug operations to complete (if any) and
>   * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
> @@ -1507,7 +1517,8 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
>  	 * If the platform does not support hotplug, report it explicitly to
>  	 * differentiate it from a transient offlining failure.
>  	 */
> -	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED))
> +	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
> +	    cpu_hotplug_offline_disabled)
>  		return -EOPNOTSUPP;
>  	if (cpu_hotplug_disabled)
>  		return -EBUSY;


IMHO it's a little bit odd to have two mechanisms in place, even in this middle
state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
done.

Or I am wondering why cannot just merge this and the next patch together, with a
proper justification?

Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
reason to replace CC_ATTR_HOTPLUG_DISABLED.

	Currently hotplug prevented based on the confidential computing
	attribute which is set for Intel TDX. But TDX is not the only possible
	user of the wake up method.

"TDX is not the only possible user of the wake up method" doesn't mean we need
to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.

To me the true reason is the new MADT wake up version actually brings the
support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
needs to disable CPU offline based on the MADT wake up version, but not the CC_*
attributes that is determined by CoCo VM type.

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> Currently offlining hotplug prevented based on the confidential
> computing attribute which is set for Intel TDX. But TDX is not
> the only possible user of the wake up method.
> 
> Introduce cpu_hotplug_not_supported() that can be called to indicate
> that CPU offlining should be disabled.
> 
> This function is going to replace CC_ATTR_HOTPLUG_DISABLED for ACPI
> MADT.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  include/linux/cpu.h |  2 ++
>  kernel/cpu.c        | 13 ++++++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index f19f56501809..97832ced939d 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -132,6 +132,7 @@ extern void cpus_read_lock(void);
>  extern void cpus_read_unlock(void);
>  extern int  cpus_read_trylock(void);
>  extern void lockdep_assert_cpus_held(void);
> +extern void cpu_hotplug_disable_offlining(void);
>  extern void cpu_hotplug_disable(void);
>  extern void cpu_hotplug_enable(void);
>  void clear_tasks_mm_cpumask(int cpu);
> @@ -147,6 +148,7 @@ static inline void cpus_read_lock(void) { }
>  static inline void cpus_read_unlock(void) { }
>  static inline int  cpus_read_trylock(void) { return true; }
>  static inline void lockdep_assert_cpus_held(void) { }
> +static inline void cpu_hotplug_disable_offlining(void) { }
>  static inline void cpu_hotplug_disable(void) { }
>  static inline void cpu_hotplug_enable(void) { }
>  static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6de7c6bb74ee..faebee0050a2 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -484,6 +484,8 @@ static int cpu_hotplug_disabled;
>  
>  DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
>  
> +static bool cpu_hotplug_offline_disabled;
> +
>  void cpus_read_lock(void)
>  {
>  	percpu_down_read(&cpu_hotplug_lock);
> @@ -543,6 +545,14 @@ static void lockdep_release_cpus_lock(void)
>  	rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
>  }
>  
> +/* Declare CPU offlining not supported */
> +void cpu_hotplug_disable_offlining(void)
> +{
> +	cpu_maps_update_begin();
> +	cpu_hotplug_offline_disabled = true;
> +	cpu_maps_update_done();
> +}
> +
>  /*
>   * Wait for currently running CPU hotplug operations to complete (if any) and
>   * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
> @@ -1507,7 +1517,8 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
>  	 * If the platform does not support hotplug, report it explicitly to
>  	 * differentiate it from a transient offlining failure.
>  	 */
> -	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED))
> +	if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) ||
> +	    cpu_hotplug_offline_disabled)
>  		return -EOPNOTSUPP;
>  	if (cpu_hotplug_disabled)
>  		return -EBUSY;


IMHO it's a little bit odd to have two mechanisms in place, even in this middle
state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
done.

Or I am wondering why cannot just merge this and the next patch together, with a
proper justification?

Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
reason to replace CC_ATTR_HOTPLUG_DISABLED.

	Currently hotplug prevented based on the confidential computing
	attribute which is set for Intel TDX. But TDX is not the only possible
	user of the wake up method.

"TDX is not the only possible user of the wake up method" doesn't mean we need
to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.

To me the true reason is the new MADT wake up version actually brings the
support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
needs to disable CPU offline based on the MADT wake up version, but not the CC_*
attributes that is determined by CoCo VM type.
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Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Mon, Oct 23, 2023, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
> >> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> >> index b8ab9ee5896c..1ee49c98e70a 100644
> >> --- a/arch/x86/kernel/kvm.c
> >> +++ b/arch/x86/kernel/kvm.c
> >> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
> >>         kvm_pv_disable_apf();
> >>         if (!shutdown)
> >>                 apf_task_wake_all();
> >> -       kvmclock_disable();
> >> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
> >> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
> >> +               kvmclock_disable();
> >>  }
> >
> > That would result in an unnecessray WRMSR in the case where kvmclock is disabled
> > on the command line.  It _should_ be benign given how the code is written, but
> > it's not impossible to imagine a scenario where someone disabled kvmclock in the
> > guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
> > MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
> > kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
> > kvmclock_disable().
> 
> True but we don't have such module params to disable other PV features so
> e.g. KVM_FEATURE_PV_EOI/KVM_FEATURE_MIGRATION_CONTROL are written to
> unconditionally. Wouldn't it be better to handle parameters like
> 'no-kvmclock' by clearing the feature bit in kvm_arch_para_features()'s
> return value so all kvm_para_has_feature() calls for it just return
> 'false'? We can even do an umbreall "no-kvm-features=<mask>" to cover
> all possible debug cases.

I don't know that it's worth the effort, or that it'd even be a net positive.

Today, kvm_para_has_feature() goes through to CPUID every time, e.g. we'd have
to add a small bit of infrastructure to snapshot and clear bits, or rework things
to let kvm_para_has_feature peek at kvmclock.

And things like KVM_FEATURE_PV_TLB_FLUSH would be quite weird, e.g. we either end
up leaving the feature bit set while returning "false" for pv_tlb_flush_supported(),
or we'd clear the feature bit for a rather large number of conditions that don't
really have anything to do with KVM_FEATURE_PV_TLB_FLUSH being available.

  static bool pv_tlb_flush_supported(void)
  {
	return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
		!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
		kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
		!boot_cpu_has(X86_FEATURE_MWAIT) &&
		(num_possible_cpus() != 1));
  }

Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

[Sean Christopherson]

On Mon, Oct 23, 2023, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote:
> >> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> >> index b8ab9ee5896c..1ee49c98e70a 100644
> >> --- a/arch/x86/kernel/kvm.c
> >> +++ b/arch/x86/kernel/kvm.c
> >> @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown)
> >>         kvm_pv_disable_apf();
> >>         if (!shutdown)
> >>                 apf_task_wake_all();
> >> -       kvmclock_disable();
> >> +       if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) ||
> >> +           kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
> >> +               kvmclock_disable();
> >>  }
> >
> > That would result in an unnecessray WRMSR in the case where kvmclock is disabled
> > on the command line.  It _should_ be benign given how the code is written, but
> > it's not impossible to imagine a scenario where someone disabled kvmclock in the
> > guest because of a hypervisor bug.  And the WRMSR would become a bogus write to
> > MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if
> > kvmclock is actually used, e.g. if someone made Kirill's change sans the check in
> > kvmclock_disable().
> 
> True but we don't have such module params to disable other PV features so
> e.g. KVM_FEATURE_PV_EOI/KVM_FEATURE_MIGRATION_CONTROL are written to
> unconditionally. Wouldn't it be better to handle parameters like
> 'no-kvmclock' by clearing the feature bit in kvm_arch_para_features()'s
> return value so all kvm_para_has_feature() calls for it just return
> 'false'? We can even do an umbreall "no-kvm-features=<mask>" to cover
> all possible debug cases.

I don't know that it's worth the effort, or that it'd even be a net positive.

Today, kvm_para_has_feature() goes through to CPUID every time, e.g. we'd have
to add a small bit of infrastructure to snapshot and clear bits, or rework things
to let kvm_para_has_feature peek at kvmclock.

And things like KVM_FEATURE_PV_TLB_FLUSH would be quite weird, e.g. we either end
up leaving the feature bit set while returning "false" for pv_tlb_flush_supported(),
or we'd clear the feature bit for a rather large number of conditions that don't
really have anything to do with KVM_FEATURE_PV_TLB_FLUSH being available.

  static bool pv_tlb_flush_supported(void)
  {
	return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
		!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
		kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
		!boot_cpu_has(X86_FEATURE_MWAIT) &&
		(num_possible_cpus() != 1));
  }

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Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[kirill.shutemov]

On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
> IMHO it's a little bit odd to have two mechanisms in place, even in this middle
> state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
> the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
> cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
> done.

I can. But I don't see how it makes a difference.

> Or I am wondering why cannot just merge this and the next patch together, with a
> proper justification?

Because the very next thing reviewers would ask is to split them :P

> Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
> reason to replace CC_ATTR_HOTPLUG_DISABLED.
> 
> 	Currently hotplug prevented based on the confidential computing
> 	attribute which is set for Intel TDX. But TDX is not the only possible
> 	user of the wake up method.
> 
> "TDX is not the only possible user of the wake up method" doesn't mean we need
> to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
> CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.
> 
> To me the true reason is the new MADT wake up version actually brings the
> support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
> needs to disable CPU offline based on the MADT wake up version, but not the CC_*
> attributes that is determined by CoCo VM type.

No. MADT is orthogonal to CoCo. It can be implemented outside of CoCo
environment and CoCo platform can implement other wake up methods. It is
not up to TDX/SEV/whatever to decide if offlining is supported. It is
property of the wakeup method implemented on the platform.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[kirill.shutemov]

On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
> IMHO it's a little bit odd to have two mechanisms in place, even in this middle
> state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
> the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
> cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
> done.

I can. But I don't see how it makes a difference.

> Or I am wondering why cannot just merge this and the next patch together, with a
> proper justification?

Because the very next thing reviewers would ask is to split them :P

> Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
> reason to replace CC_ATTR_HOTPLUG_DISABLED.
> 
> 	Currently hotplug prevented based on the confidential computing
> 	attribute which is set for Intel TDX. But TDX is not the only possible
> 	user of the wake up method.
> 
> "TDX is not the only possible user of the wake up method" doesn't mean we need
> to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
> CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.
> 
> To me the true reason is the new MADT wake up version actually brings the
> support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
> needs to disable CPU offline based on the MADT wake up version, but not the CC_*
> attributes that is determined by CoCo VM type.

No. MADT is orthogonal to CoCo. It can be implemented outside of CoCo
environment and CoCo platform can implement other wake up methods. It is
not up to TDX/SEV/whatever to decide if offlining is supported. It is
property of the wakeup method implemented on the platform.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Huang, Kai]

On Mon, 2023-10-23 at 18:31 +0300, kirill.shutemov@linux.intel.com wrote:
> On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
> > IMHO it's a little bit odd to have two mechanisms in place, even in this middle
> > state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
> > the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
> > cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
> > done.
> 
> I can. But I don't see how it makes a difference.

Personally I think this is better because it is odd to have two mechanisms in
place even temporarily especially when we can avoid it.  But no hard opinion. 
Up to you.

> 
> > Or I am wondering why cannot just merge this and the next patch together, with a
> > proper justification?
> 
> Because the very next thing reviewers would ask is to split them :P
> 
> > Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
> > reason to replace CC_ATTR_HOTPLUG_DISABLED.
> > 
> > 	Currently hotplug prevented based on the confidential computing
> > 	attribute which is set for Intel TDX. But TDX is not the only possible
> > 	user of the wake up method.
> > 
> > "TDX is not the only possible user of the wake up method" doesn't mean we need
> > to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
> > CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.
> > 
> > To me the true reason is the new MADT wake up version actually brings the
> > support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
> > needs to disable CPU offline based on the MADT wake up version, but not the CC_*
> > attributes that is determined by CoCo VM type.
> 
> No. MADT is orthogonal to CoCo. It can be implemented outside of CoCo
> environment and CoCo platform can implement other wake up methods. It is
> not up to TDX/SEV/whatever to decide if offlining is supported. It is
> property of the wakeup method implemented on the platform.
> 

Yeah sure.  Can we put this to changelog to make it clearer? :-)

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Huang, Kai]

On Mon, 2023-10-23 at 18:31 +0300, kirill.shutemov@linux.intel.com wrote:
> On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
> > IMHO it's a little bit odd to have two mechanisms in place, even in this middle
> > state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
> > the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
> > cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
> > done.
> 
> I can. But I don't see how it makes a difference.

Personally I think this is better because it is odd to have two mechanisms in
place even temporarily especially when we can avoid it.  But no hard opinion. 
Up to you.

> 
> > Or I am wondering why cannot just merge this and the next patch together, with a
> > proper justification?
> 
> Because the very next thing reviewers would ask is to split them :P
> 
> > Btw, IMHO the changelog (this and next patch's) seems didn't explain the true
> > reason to replace CC_ATTR_HOTPLUG_DISABLED.
> > 
> > 	Currently hotplug prevented based on the confidential computing
> > 	attribute which is set for Intel TDX. But TDX is not the only possible
> > 	user of the wake up method.
> > 
> > "TDX is not the only possible user of the wake up method" doesn't mean we need
> > to replace CC_ATTR_HOTPLUG_DISABLED.  E.g., other CoCo VM type can also select
> > CC_ATTR_HOTPLUG_DISABLED if it uses MADT wake up method.
> > 
> > To me the true reason is the new MADT wake up version actually brings the
> > support of offlining cpu, thus it's more suitable to decide whether the CoCo VM
> > needs to disable CPU offline based on the MADT wake up version, but not the CC_*
> > attributes that is determined by CoCo VM type.
> 
> No. MADT is orthogonal to CoCo. It can be implemented outside of CoCo
> environment and CoCo platform can implement other wake up methods. It is
> not up to TDX/SEV/whatever to decide if offlining is supported. It is
> property of the wakeup method implemented on the platform.
> 

Yeah sure.  Can we put this to changelog to make it clearer? :-)
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Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Huang, Kai]

> --- /dev/null
> +++ b/arch/x86/kernel/acpi/madt.S

I think the name 'madt.S' is too generic.  How about something be more specific
such as madt_reset.S, or madt_playdead.S, etc? 

> @@ -0,0 +1,24 @@
> +#include <linux/linkage.h>
> +#include <asm/nospec-branch.h>
> +#include <asm/page_types.h>
> +#include <asm/processor-flags.h>
> +
> +	.text
> +	.align PAGE_SIZE
> +SYM_FUNC_START(asm_acpi_mp_play_dead)
> +	/* Load address of reset vector into RCX to jump when kernel is ready */
> +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> +
> +	/* Turn off global entries. Following CR3 write will flush them. */
> +	movq	%cr4, %rdx
> +	andq	$~(X86_CR4_PGE), %rdx
> +	movq	%rdx, %cr4
> +
> +	/* Switch to identity mapping */
> +	movq	acpi_mp_pgd(%rip), %rax
> +	movq	%rax, %cr3

Do we need to switch back to kernel direct-map page table after CPU is wake up
again?  We do support normal CPU offline/online, but not limited to kexec,
right?

> +
> +	/* Jump to reset vector */
> +	ANNOTATE_RETPOLINE_SAFE
> +	jmp	*%rcx
> +SYM_FUNC_END(asm_acpi_mp_play_dead)
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index ad170def2367..f9ff14ee2892 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -1,8 +1,13 @@
>  #include <linux/acpi.h>
>  #include <linux/cpu.h>
> +#include <linux/delay.h>
>  #include <linux/io.h>
> +#include <linux/memblock.h>
> +#include <linux/pgtable.h>
> +#include <linux/sched/hotplug.h>
>  #include <asm/apic.h>
>  #include <asm/barrier.h>
> +#include <asm/init.h>
>  #include <asm/processor.h>
>  
>  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
>  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
>  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
> +u64 acpi_mp_pgd;
> +u64 acpi_mp_reset_vector_paddr;
> +
> +void asm_acpi_mp_play_dead(void);
> +
> +static void __init *alloc_pgt_page(void *context)
> +{
> +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> +}
> +
> +/*
> + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> + * the same place as in the kernel page tables. The function switches to
> + * the identity mapping 
> 

This function itself doesn't switch to the identity mapping.  It just creates
the kernel mapping for asm_acpi_mp_play_dead() in the identify mapping page
table.

> and has be present at the same spot in before and
> + * after transition.

This part doesn't parse to me.  I guess the whole comment can be:

	asm_acpi_mp_play_dead() is accessed both before and after switching to 
	the identity mapping.  Also map it at the kernel virtual address in
	the identity mapping table.

Or perhaps even better, put the above comments to the place where this function
is called?

> + */
> +static int __init init_transition_pgtable(pgd_t *pgd)
> +{
> +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> +	unsigned long vaddr, paddr;
> +	int result = -ENOMEM;
> +	p4d_t *p4d;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +
> +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> +	pgd += pgd_index(vaddr);
> +	if (!pgd_present(*pgd)) {
> +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> +		if (!p4d)
> +			goto err;
> +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> +	}
> +	p4d = p4d_offset(pgd, vaddr);
> +	if (!p4d_present(*p4d)) {
> +		pud = (pud_t *)alloc_pgt_page(NULL);
> +		if (!pud)
> +			goto err;
> +		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
> +	}
> +	pud = pud_offset(p4d, vaddr);
> +	if (!pud_present(*pud)) {
> +		pmd = (pmd_t *)alloc_pgt_page(NULL);
> +		if (!pmd)
> +			goto err;
> +		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
> +	}
> +	pmd = pmd_offset(pud, vaddr);
> +	if (!pmd_present(*pmd)) {
> +		pte = (pte_t *)alloc_pgt_page(NULL);
> +		if (!pte)
> +			goto err;
> +		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
> +	}
> +	pte = pte_offset_kernel(pmd, vaddr);
> +
> +	paddr = __pa(vaddr);
> +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> +
> +	return 0;
> +err:
> +	return result;
> +}
> +
> +static void acpi_mp_play_dead(void)
> +{
> +	play_dead_common();
> +	asm_acpi_mp_play_dead();
> +}
> +
> +static void acpi_mp_cpu_die(unsigned int cpu)
> +{
> +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
> +	unsigned long timeout;
> +
> +	/*
> +	 * Use TEST mailbox command to prove that BIOS got control over
> +	 * the CPU before declaring it dead.
> +	 *
> +	 * BIOS has to clear 'command' field of the mailbox.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id = apicid;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_TEST);
> +
> +	/* Don't wait longer than a second. */
> +	timeout = USEC_PER_SEC;
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> +		udelay(1);
> +}
> +
> +static void acpi_mp_stop_other_cpus(int wait)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());
> +}
> +
> +static void acpi_mp_crash_stop_other_cpus(void)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());
> +
> +	/* The kernel is broken so disable interrupts */
> +	local_irq_disable();
> +}
> +
> +static int __init acpi_mp_setup_reset(u64 reset_vector)
> +{
> +	pgd_t *pgd;
> +	struct x86_mapping_info info = {
> +		.alloc_pgt_page = alloc_pgt_page,
> +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> +	};
> +
> +	pgd = alloc_pgt_page(NULL);
> +
> +	for (int i = 0; i < nr_pfn_mapped; i++) {
> +		unsigned long mstart, mend;
> +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> +			return -ENOMEM;
> +	}

This is for kexec() IIUC.  Add a comment?

If we consider normal CPU offline/online case, then I don't think we need the
identity mapping for all memory?

> +
> +	if (kernel_ident_mapping_init(&info, pgd,
> +				      PAGE_ALIGN_DOWN(reset_vector),
> +				      PAGE_ALIGN(reset_vector + 1))) {
> +		return -ENOMEM;
> +	}
> +
> +	if (init_transition_pgtable(pgd))
> +		return -ENOMEM;
> +
> +	smp_ops.play_dead = acpi_mp_play_dead;
> +	smp_ops.cpu_die = acpi_mp_cpu_die;
> +	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
> +	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
> +
> +	acpi_mp_reset_vector_paddr = reset_vector;
> +	acpi_mp_pgd = __pa(pgd);
> +
> +	return 0;
> +}
> +
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
>  	if (!acpi_mp_wake_mailbox_paddr) {
> @@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	struct acpi_madt_multiproc_wakeup *mp_wake;
>  
>  	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> +	if (!mp_wake)
> +		return -EINVAL;
> +
> +	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
> +		return -EINVAL;
> +	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
>  		return -EINVAL;
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
>  	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
> -	cpu_hotplug_disable_offlining();
> +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> +		acpi_mp_setup_reset(mp_wake->reset_vector);

It's better to fallback to "disable offline" if this function fails.

Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Huang, Kai]

> --- /dev/null
> +++ b/arch/x86/kernel/acpi/madt.S

I think the name 'madt.S' is too generic.  How about something be more specific
such as madt_reset.S, or madt_playdead.S, etc? 

> @@ -0,0 +1,24 @@
> +#include <linux/linkage.h>
> +#include <asm/nospec-branch.h>
> +#include <asm/page_types.h>
> +#include <asm/processor-flags.h>
> +
> +	.text
> +	.align PAGE_SIZE
> +SYM_FUNC_START(asm_acpi_mp_play_dead)
> +	/* Load address of reset vector into RCX to jump when kernel is ready */
> +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> +
> +	/* Turn off global entries. Following CR3 write will flush them. */
> +	movq	%cr4, %rdx
> +	andq	$~(X86_CR4_PGE), %rdx
> +	movq	%rdx, %cr4
> +
> +	/* Switch to identity mapping */
> +	movq	acpi_mp_pgd(%rip), %rax
> +	movq	%rax, %cr3

Do we need to switch back to kernel direct-map page table after CPU is wake up
again?  We do support normal CPU offline/online, but not limited to kexec,
right?

> +
> +	/* Jump to reset vector */
> +	ANNOTATE_RETPOLINE_SAFE
> +	jmp	*%rcx
> +SYM_FUNC_END(asm_acpi_mp_play_dead)
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index ad170def2367..f9ff14ee2892 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -1,8 +1,13 @@
>  #include <linux/acpi.h>
>  #include <linux/cpu.h>
> +#include <linux/delay.h>
>  #include <linux/io.h>
> +#include <linux/memblock.h>
> +#include <linux/pgtable.h>
> +#include <linux/sched/hotplug.h>
>  #include <asm/apic.h>
>  #include <asm/barrier.h>
> +#include <asm/init.h>
>  #include <asm/processor.h>
>  
>  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
>  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
>  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
> +u64 acpi_mp_pgd;
> +u64 acpi_mp_reset_vector_paddr;
> +
> +void asm_acpi_mp_play_dead(void);
> +
> +static void __init *alloc_pgt_page(void *context)
> +{
> +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> +}
> +
> +/*
> + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> + * the same place as in the kernel page tables. The function switches to
> + * the identity mapping 
> 

This function itself doesn't switch to the identity mapping.  It just creates
the kernel mapping for asm_acpi_mp_play_dead() in the identify mapping page
table.

> and has be present at the same spot in before and
> + * after transition.

This part doesn't parse to me.  I guess the whole comment can be:

	asm_acpi_mp_play_dead() is accessed both before and after switching to 
	the identity mapping.  Also map it at the kernel virtual address in
	the identity mapping table.

Or perhaps even better, put the above comments to the place where this function
is called?

> + */
> +static int __init init_transition_pgtable(pgd_t *pgd)
> +{
> +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> +	unsigned long vaddr, paddr;
> +	int result = -ENOMEM;
> +	p4d_t *p4d;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +
> +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> +	pgd += pgd_index(vaddr);
> +	if (!pgd_present(*pgd)) {
> +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> +		if (!p4d)
> +			goto err;
> +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> +	}
> +	p4d = p4d_offset(pgd, vaddr);
> +	if (!p4d_present(*p4d)) {
> +		pud = (pud_t *)alloc_pgt_page(NULL);
> +		if (!pud)
> +			goto err;
> +		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
> +	}
> +	pud = pud_offset(p4d, vaddr);
> +	if (!pud_present(*pud)) {
> +		pmd = (pmd_t *)alloc_pgt_page(NULL);
> +		if (!pmd)
> +			goto err;
> +		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
> +	}
> +	pmd = pmd_offset(pud, vaddr);
> +	if (!pmd_present(*pmd)) {
> +		pte = (pte_t *)alloc_pgt_page(NULL);
> +		if (!pte)
> +			goto err;
> +		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
> +	}
> +	pte = pte_offset_kernel(pmd, vaddr);
> +
> +	paddr = __pa(vaddr);
> +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> +
> +	return 0;
> +err:
> +	return result;
> +}
> +
> +static void acpi_mp_play_dead(void)
> +{
> +	play_dead_common();
> +	asm_acpi_mp_play_dead();
> +}
> +
> +static void acpi_mp_cpu_die(unsigned int cpu)
> +{
> +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
> +	unsigned long timeout;
> +
> +	/*
> +	 * Use TEST mailbox command to prove that BIOS got control over
> +	 * the CPU before declaring it dead.
> +	 *
> +	 * BIOS has to clear 'command' field of the mailbox.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id = apicid;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_TEST);
> +
> +	/* Don't wait longer than a second. */
> +	timeout = USEC_PER_SEC;
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> +		udelay(1);
> +}
> +
> +static void acpi_mp_stop_other_cpus(int wait)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());
> +}
> +
> +static void acpi_mp_crash_stop_other_cpus(void)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());
> +
> +	/* The kernel is broken so disable interrupts */
> +	local_irq_disable();
> +}
> +
> +static int __init acpi_mp_setup_reset(u64 reset_vector)
> +{
> +	pgd_t *pgd;
> +	struct x86_mapping_info info = {
> +		.alloc_pgt_page = alloc_pgt_page,
> +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> +	};
> +
> +	pgd = alloc_pgt_page(NULL);
> +
> +	for (int i = 0; i < nr_pfn_mapped; i++) {
> +		unsigned long mstart, mend;
> +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> +			return -ENOMEM;
> +	}

This is for kexec() IIUC.  Add a comment?

If we consider normal CPU offline/online case, then I don't think we need the
identity mapping for all memory?

> +
> +	if (kernel_ident_mapping_init(&info, pgd,
> +				      PAGE_ALIGN_DOWN(reset_vector),
> +				      PAGE_ALIGN(reset_vector + 1))) {
> +		return -ENOMEM;
> +	}
> +
> +	if (init_transition_pgtable(pgd))
> +		return -ENOMEM;
> +
> +	smp_ops.play_dead = acpi_mp_play_dead;
> +	smp_ops.cpu_die = acpi_mp_cpu_die;
> +	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
> +	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
> +
> +	acpi_mp_reset_vector_paddr = reset_vector;
> +	acpi_mp_pgd = __pa(pgd);
> +
> +	return 0;
> +}
> +
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
>  	if (!acpi_mp_wake_mailbox_paddr) {
> @@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	struct acpi_madt_multiproc_wakeup *mp_wake;
>  
>  	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> +	if (!mp_wake)
> +		return -EINVAL;
> +
> +	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
> +		return -EINVAL;
> +	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
>  		return -EINVAL;
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
>  	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
> -	cpu_hotplug_disable_offlining();
> +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> +		acpi_mp_setup_reset(mp_wake->reset_vector);

It's better to fallback to "disable offline" if this function fails.

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Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> 
> Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> that the mailbox is not usable.  This prevents the kexec()-ed kernel
> from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> only be able to use the boot CPU.
> 
> This is Linux-specific protocol and not reflected in ACPI spec.
> 
> Booting the second kernel with signle CPU is enough to cover the most
> common case for kexec -- kdump.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Reviewed-by: Kai Huang <kai.huang@intel.com>

Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> 
> Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> that the mailbox is not usable.  This prevents the kexec()-ed kernel
> from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> only be able to use the boot CPU.
> 
> This is Linux-specific protocol and not reflected in ACPI spec.
> 
> Booting the second kernel with signle CPU is enough to cover the most
> common case for kexec -- kdump.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Reviewed-by: Kai Huang <kai.huang@intel.com>

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Re: [PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> To prepare for the addition of support for MADT wakeup structure version
> 1, it is necessary to provide more appropriate names for the fields in
> the structure.
> 
> The field 'mailbox_version' renamed as 'version'. This field signifies
> the version of the structure and the related protocols, rather than the
> version of the mailbox. This field has not been utilized in the code
> thus far.
> 
> The field 'base_address' renamed as 'mailbox_address' to clarify the
> kind of address it represents. In version 1, the structure includes the
> reset vector address. Clear and distinct naming helps to prevent any
> confusion.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
>  include/acpi/actbl2.h              | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 9bbe829737e7..ad170def2367 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
>  	cpu_hotplug_disable_offlining();
>  
> @@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	 *
>  	 * This is Linux-specific protocol and not reflected in ACPI spec.
>  	 */
> -	mp_wake->base_address = 0;
> +	mp_wake->mailbox_address = 0;
>  
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
> index 3751ae69432f..23b4cfb640fc 100644
> --- a/include/acpi/actbl2.h
> +++ b/include/acpi/actbl2.h
> @@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
>  
>  struct acpi_madt_multiproc_wakeup {
>  	struct acpi_subtable_header header;
> -	u16 mailbox_version;
> +	u16 version;
>  	u32 reserved;		/* reserved - must be zero */
> -	u64 base_address;
> +	u64 mailbox_address;
>  };
>  
>  #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032

Reviewed-by: Kai Huang <kai.huang@intel.com>

Nit:

Looks this patch can be moved to an earlier place because IMHO the justification
you provided in the changelog also makes sense even w/o the new wake up
structure version.  Anyway up to you.

Re: [PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Huang, Kai]

On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> To prepare for the addition of support for MADT wakeup structure version
> 1, it is necessary to provide more appropriate names for the fields in
> the structure.
> 
> The field 'mailbox_version' renamed as 'version'. This field signifies
> the version of the structure and the related protocols, rather than the
> version of the mailbox. This field has not been utilized in the code
> thus far.
> 
> The field 'base_address' renamed as 'mailbox_address' to clarify the
> kind of address it represents. In version 1, the structure includes the
> reset vector address. Clear and distinct naming helps to prevent any
> confusion.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
>  include/acpi/actbl2.h              | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 9bbe829737e7..ad170def2367 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
>  	cpu_hotplug_disable_offlining();
>  
> @@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	 *
>  	 * This is Linux-specific protocol and not reflected in ACPI spec.
>  	 */
> -	mp_wake->base_address = 0;
> +	mp_wake->mailbox_address = 0;
>  
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
> index 3751ae69432f..23b4cfb640fc 100644
> --- a/include/acpi/actbl2.h
> +++ b/include/acpi/actbl2.h
> @@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
>  
>  struct acpi_madt_multiproc_wakeup {
>  	struct acpi_subtable_header header;
> -	u16 mailbox_version;
> +	u16 version;
>  	u32 reserved;		/* reserved - must be zero */
> -	u64 base_address;
> +	u64 mailbox_address;
>  };
>  
>  #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032

Reviewed-by: Kai Huang <kai.huang@intel.com>

Nit:

Looks this patch can be moved to an earlier place because IMHO the justification
you provided in the changelog also makes sense even w/o the new wake up
structure version.  Anyway up to you.
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Re: [PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> To prepare for the addition of support for MADT wakeup structure version
> 1, it is necessary to provide more appropriate names for the fields in
> the structure.
> 
> The field 'mailbox_version' renamed as 'version'. This field signifies
> the version of the structure and the related protocols, rather than the
> version of the mailbox. This field has not been utilized in the code
> thus far.
> 
> The field 'base_address' renamed as 'mailbox_address' to clarify the
> kind of address it represents. In version 1, the structure includes the
> reset vector address. Clear and distinct naming helps to prevent any
> confusion.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
>  include/acpi/actbl2.h              | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 9bbe829737e7..ad170def2367 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
>  	cpu_hotplug_disable_offlining();
>  
> @@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	 *
>  	 * This is Linux-specific protocol and not reflected in ACPI spec.
>  	 */
> -	mp_wake->base_address = 0;
> +	mp_wake->mailbox_address = 0;
>  
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
> index 3751ae69432f..23b4cfb640fc 100644
> --- a/include/acpi/actbl2.h
> +++ b/include/acpi/actbl2.h
> @@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
>  
>  struct acpi_madt_multiproc_wakeup {
>  	struct acpi_subtable_header header;
> -	u16 mailbox_version;
> +	u16 version;
>  	u32 reserved;		/* reserved - must be zero */
> -	u64 base_address;
> +	u64 mailbox_address;
>  };
>  
>  #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

Re: [PATCHv2 12/13] x86/acpi: Rename fields in acpi_madt_multiproc_wakeup structure

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> To prepare for the addition of support for MADT wakeup structure version
> 1, it is necessary to provide more appropriate names for the fields in
> the structure.
> 
> The field 'mailbox_version' renamed as 'version'. This field signifies
> the version of the structure and the related protocols, rather than the
> version of the mailbox. This field has not been utilized in the code
> thus far.
> 
> The field 'base_address' renamed as 'mailbox_address' to clarify the
> kind of address it represents. In version 1, the structure includes the
> reset vector address. Clear and distinct naming helps to prevent any
> confusion.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  arch/x86/kernel/acpi/madt_wakeup.c | 4 ++--
>  include/acpi/actbl2.h              | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 9bbe829737e7..ad170def2367 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -79,7 +79,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
> -	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
>  	cpu_hotplug_disable_offlining();
>  
> @@ -98,7 +98,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	 *
>  	 * This is Linux-specific protocol and not reflected in ACPI spec.
>  	 */
> -	mp_wake->base_address = 0;
> +	mp_wake->mailbox_address = 0;
>  
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
> index 3751ae69432f..23b4cfb640fc 100644
> --- a/include/acpi/actbl2.h
> +++ b/include/acpi/actbl2.h
> @@ -1109,9 +1109,9 @@ struct acpi_madt_generic_translator {
>  
>  struct acpi_madt_multiproc_wakeup {
>  	struct acpi_subtable_header header;
> -	u16 mailbox_version;
> +	u16 version;
>  	u32 reserved;		/* reserved - must be zero */
> -	u64 base_address;
> +	u64 mailbox_address;
>  };
>  
>  #define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE        2032

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> 
> Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> that the mailbox is not usable.  This prevents the kexec()-ed kernel
> from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> only be able to use the boot CPU.
> 
> This is Linux-specific protocol and not reflected in ACPI spec.
> 
> Booting the second kernel with signle CPU is enough to cover the most
> common case for kexec -- kdump.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 4bc1d5106afd..9bbe829737e7 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
> +	if (!acpi_mp_wake_mailbox_paddr) {
> +		pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
> +		return -EOPNOTSUPP;
> +	}
> +
>  	/*
>  	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
>  	 *
> @@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	cpu_hotplug_disable_offlining();
>  
> +	/*
> +	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> +	 * It limits kexec: the second kernel won't be able to use more than
> +	 * one CPU.
> +	 *
> +	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> +	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> +	 *
> +	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> +	 * indicate that the mailbox is not usable.  This prevents the
> +	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> +	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> +	 *
> +	 * This is Linux-specific protocol and not reflected in ACPI spec.
> +	 */
> +	mp_wake->base_address = 0;

Is there any way to skip secondary CPU bring-up for kexec case instead of
returning error in ->wakeup_secondary_cpu_64()?

> +
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
>  	return 0;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Kuppuswamy Sathyanarayanan]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> 
> Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> that the mailbox is not usable.  This prevents the kexec()-ed kernel
> from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> only be able to use the boot CPU.
> 
> This is Linux-specific protocol and not reflected in ACPI spec.
> 
> Booting the second kernel with signle CPU is enough to cover the most
> common case for kexec -- kdump.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 4bc1d5106afd..9bbe829737e7 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
> +	if (!acpi_mp_wake_mailbox_paddr) {
> +		pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
> +		return -EOPNOTSUPP;
> +	}
> +
>  	/*
>  	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
>  	 *
> @@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	cpu_hotplug_disable_offlining();
>  
> +	/*
> +	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> +	 * It limits kexec: the second kernel won't be able to use more than
> +	 * one CPU.
> +	 *
> +	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> +	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> +	 *
> +	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> +	 * indicate that the mailbox is not usable.  This prevents the
> +	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> +	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> +	 *
> +	 * This is Linux-specific protocol and not reflected in ACPI spec.
> +	 */
> +	mp_wake->base_address = 0;

Is there any way to skip secondary CPU bring-up for kexec case instead of
returning error in ->wakeup_secondary_cpu_64()?

> +
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
>  	return 0;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Huang, Kai]

> > +	.text
> > +	.align PAGE_SIZE
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> 
> Do we need to switch back to kernel direct-map page table after CPU is wake up
> again?  We do support normal CPU offline/online, but not limited to kexec,
> right?

Please ignore this.  I found if I am reading right even for TDX guest the new
online cpu will start with trampoline_start64 assembly, so it will load kernel
page table anyway.  Sorry for the noise.

[...]


> > +	for (int i = 0; i < nr_pfn_mapped; i++) {
> > +		unsigned long mstart, mend;
> > +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> > +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> > +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> > +			return -ENOMEM;
> > +	}
> 
> This is for kexec() IIUC.  Add a comment?
> 
> If we consider normal CPU offline/online case, then I don't think we need the
> identity mapping for all memory?
> 

Also this one. :-)

> 

Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Huang, Kai]

> > +	.text
> > +	.align PAGE_SIZE
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> 
> Do we need to switch back to kernel direct-map page table after CPU is wake up
> again?  We do support normal CPU offline/online, but not limited to kexec,
> right?

Please ignore this.  I found if I am reading right even for TDX guest the new
online cpu will start with trampoline_start64 assembly, so it will load kernel
page table anyway.  Sorry for the noise.

[...]


> > +	for (int i = 0; i < nr_pfn_mapped; i++) {
> > +		unsigned long mstart, mend;
> > +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> > +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> > +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> > +			return -ENOMEM;
> > +	}
> 
> This is for kexec() IIUC.  Add a comment?
> 
> If we consider normal CPU offline/online case, then I don't think we need the
> identity mapping for all memory?
> 

Also this one. :-)

> 

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Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[kirill.shutemov]

On Tue, Oct 24, 2023 at 10:11:58AM +0000, Huang, Kai wrote:
> 
> > --- /dev/null
> > +++ b/arch/x86/kernel/acpi/madt.S
> 
> I think the name 'madt.S' is too generic.  How about something be more specific
> such as madt_reset.S, or madt_playdead.S, etc? 

Okay, madt_playdead.S sounds good.

> > @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
> >  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> >  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> > +u64 acpi_mp_pgd;
> > +u64 acpi_mp_reset_vector_paddr;
> > +
> > +void asm_acpi_mp_play_dead(void);
> > +
> > +static void __init *alloc_pgt_page(void *context)
> > +{
> > +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +}
> > +
> > +/*
> > + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> > + * the same place as in the kernel page tables. The function switches to
> > + * the identity mapping 
> > 
> 
> This function itself doesn't switch to the identity mapping.  It just creates
> the kernel mapping for asm_acpi_mp_play_dead() in the identify mapping page
> table.

By "The function" I meant asm_acpi_mp_play_dead(). Yeah, it is not clear.

Will so s/The function/asm_acpi_mp_play_dead()/

> > -	cpu_hotplug_disable_offlining();
> > +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> > +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> > +		acpi_mp_setup_reset(mp_wake->reset_vector);
> 
> It's better to fallback to "disable offline" if this function fails.
> 

Okay, will warn to disable offlining.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[kirill.shutemov]

On Tue, Oct 24, 2023 at 10:11:58AM +0000, Huang, Kai wrote:
> 
> > --- /dev/null
> > +++ b/arch/x86/kernel/acpi/madt.S
> 
> I think the name 'madt.S' is too generic.  How about something be more specific
> such as madt_reset.S, or madt_playdead.S, etc? 

Okay, madt_playdead.S sounds good.

> > @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
> >  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> >  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> > +u64 acpi_mp_pgd;
> > +u64 acpi_mp_reset_vector_paddr;
> > +
> > +void asm_acpi_mp_play_dead(void);
> > +
> > +static void __init *alloc_pgt_page(void *context)
> > +{
> > +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +}
> > +
> > +/*
> > + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> > + * the same place as in the kernel page tables. The function switches to
> > + * the identity mapping 
> > 
> 
> This function itself doesn't switch to the identity mapping.  It just creates
> the kernel mapping for asm_acpi_mp_play_dead() in the identify mapping page
> table.

By "The function" I meant asm_acpi_mp_play_dead(). Yeah, it is not clear.

Will so s/The function/asm_acpi_mp_play_dead()/

> > -	cpu_hotplug_disable_offlining();
> > +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> > +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> > +		acpi_mp_setup_reset(mp_wake->reset_vector);
> 
> It's better to fallback to "disable offline" if this function fails.
> 

Okay, will warn to disable offlining.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

[Kirill A. Shutemov]

On Tue, Oct 24, 2023 at 06:59:58AM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> > ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> > kexec: the second kernel won't be able to use more than one CPU.
> > 
> > Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> > The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> > 
> > Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> > that the mailbox is not usable.  This prevents the kexec()-ed kernel
> > from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> > only be able to use the boot CPU.
> > 
> > This is Linux-specific protocol and not reflected in ACPI spec.
> > 
> > Booting the second kernel with signle CPU is enough to cover the most
> > common case for kexec -- kdump.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> >  arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > index 4bc1d5106afd..9bbe829737e7 100644
> > --- a/arch/x86/kernel/acpi/madt_wakeup.c
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> >  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> >  {
> > +	if (!acpi_mp_wake_mailbox_paddr) {
> > +		pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> >  	/*
> >  	 * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> >  	 *
> > @@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> >  
> >  	cpu_hotplug_disable_offlining();
> >  
> > +	/*
> > +	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> > +	 * It limits kexec: the second kernel won't be able to use more than
> > +	 * one CPU.
> > +	 *
> > +	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> > +	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> > +	 *
> > +	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> > +	 * indicate that the mailbox is not usable.  This prevents the
> > +	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> > +	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> > +	 *
> > +	 * This is Linux-specific protocol and not reflected in ACPI spec.
> > +	 */
> > +	mp_wake->base_address = 0;
> 
> Is there any way to skip secondary CPU bring-up for kexec case instead of
> returning error in ->wakeup_secondary_cpu_64()?

I have not found a cleaner way. Do you have ideas?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Thomas Gleixner]

On Mon, Oct 23 2023 at 22:07, Kai Huang wrote:
> On Mon, 2023-10-23 at 18:31 +0300, kirill.shutemov@linux.intel.com wrote:
>> On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
>> > IMHO it's a little bit odd to have two mechanisms in place, even in this middle
>> > state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
>> > the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
>> > cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
>> > done.
>> 
>> I can. But I don't see how it makes a difference.
>
> Personally I think this is better because it is odd to have two mechanisms in
> place even temporarily especially when we can avoid it.  But no hard opinion. 
> Up to you.

It's not at all better because having this clear split makes it simpler
to review and ponder the individual changes.

Thanks,

        tglx

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Thomas Gleixner]

On Mon, Oct 23 2023 at 22:07, Kai Huang wrote:
> On Mon, 2023-10-23 at 18:31 +0300, kirill.shutemov@linux.intel.com wrote:
>> On Mon, Oct 23, 2023 at 09:30:59AM +0000, Huang, Kai wrote:
>> > IMHO it's a little bit odd to have two mechanisms in place, even in this middle
>> > state patch.  Is it better to completely replace CC_ATTR_HOTPLUG_DISABLED with
>> > the new cpu_hotplug_offline_disabled in this patch? You can explicitly call
>> > cpu_hotplug_disable_offlining() in tdx_early_init() so no functional change is
>> > done.
>> 
>> I can. But I don't see how it makes a difference.
>
> Personally I think this is better because it is odd to have two mechanisms in
> place even temporarily especially when we can avoid it.  But no hard opinion. 
> Up to you.

It's not at all better because having this clear split makes it simpler
to review and ponder the individual changes.

Thanks,

        tglx



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Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Thomas Gleixner]

On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:

Subject: cpu/hotplug: ...

> ACPI MADT doesn't allow to offline CPU after it got woke up.

ACPI MADT is a table ...

This is about the MADT mailbox wakeup method, right?

> Currently offlining hotplug prevented based on the confidential

is prevented

> computing attribute which is set for Intel TDX. But TDX is not
> the only possible user of the wake up method.
>
> Introduce cpu_hotplug_not_supported() that can be called to indicate
> that CPU offlining should be disabled.

Otherwise the changes look good!

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Thomas Gleixner]

On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:

Subject: cpu/hotplug: ...

> ACPI MADT doesn't allow to offline CPU after it got woke up.

ACPI MADT is a table ...

This is about the MADT mailbox wakeup method, right?

> Currently offlining hotplug prevented based on the confidential

is prevented

> computing attribute which is set for Intel TDX. But TDX is not
> the only possible user of the wake up method.
>
> Introduce cpu_hotplug_not_supported() that can be called to indicate
> that CPU offlining should be disabled.

Otherwise the changes look good!

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Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Kirill A. Shutemov]

On Sat, Oct 28, 2023 at 04:12:10PM +0200, Thomas Gleixner wrote:
> On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:
> 
> Subject: cpu/hotplug: ...
> 
> > ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> ACPI MADT is a table ...
> 
> This is about the MADT mailbox wakeup method, right?
> 
> > Currently offlining hotplug prevented based on the confidential
> 
> is prevented
> 
> > computing attribute which is set for Intel TDX. But TDX is not
> > the only possible user of the wake up method.
> >
> > Introduce cpu_hotplug_not_supported() that can be called to indicate
> > that CPU offlining should be disabled.
> 
> Otherwise the changes look good!

Thanks!

Thomas, could you take a look if the last patch in the series is sane?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCHv2 02/13] kernel/cpu: Add support for declaring CPU offlining not supported

[Kirill A. Shutemov]

On Sat, Oct 28, 2023 at 04:12:10PM +0200, Thomas Gleixner wrote:
> On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:
> 
> Subject: cpu/hotplug: ...
> 
> > ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> ACPI MADT is a table ...
> 
> This is about the MADT mailbox wakeup method, right?
> 
> > Currently offlining hotplug prevented based on the confidential
> 
> is prevented
> 
> > computing attribute which is set for Intel TDX. But TDX is not
> > the only possible user of the wake up method.
> >
> > Introduce cpu_hotplug_not_supported() that can be called to indicate
> > that CPU offlining should be disabled.
> 
> Otherwise the changes look good!

Thanks!

Thomas, could you take a look if the last patch in the series is sane?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Thomas Gleixner]

On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:

> MADT Multiprocessor Wakeup structure version 1 brings support of CPU
> offlining: BIOS provides a reset vector where the CPU has to jump to
> offline itself. The new TEST mailbox command can be used to test the CPU
> offlined successfully and BIOS has control over it.
>
> Add CPU offling support for ACPI MADT wakeup method by implementing
> custom cpu_die, play_dead and stop_other_cpus SMP operations.
>
> CPU offlining makes possible to hand over secondary CPUs over kexec, not

makes it possible

> limiting the second kernel with single CPU.

s/with/to/

> The change conforms to the approved ACPI spec change proposal. See the
> +SYM_FUNC_START(asm_acpi_mp_play_dead)
> +	/* Load address of reset vector into RCX to jump when kernel is ready */
> +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> +
> +	/* Turn off global entries. Following CR3 write will flush them. */
> +	movq	%cr4, %rdx
> +	andq	$~(X86_CR4_PGE), %rdx
> +	movq	%rdx, %cr4
> +
> +	/* Switch to identity mapping */
> +	movq	acpi_mp_pgd(%rip), %rax
> +	movq	%rax, %cr3

You can just make this function:

    asm_acpi_mp_play_dead(u64 reset_vector, u64 pgd_pa);

then you have the reset vector in RDI and the pgd in RSI and spare the
global variables.

>  
>  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
>  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
>  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
> +u64 acpi_mp_pgd;
> +u64 acpi_mp_reset_vector_paddr;

See above (static) and __ro_after_init please

> +
> +void asm_acpi_mp_play_dead(void);
> +
> +static void __init *alloc_pgt_page(void *context)
> +{

What's the purpose of the context argument?

> +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> +}
> +
> +/*
> + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> + * the same place as in the kernel page tables. The function switches to
> + * the identity mapping and has be present at the same spot in before and
> + * after transition.

Why does it need to be there after the CPU jumped to the reset vector?

> + */
> +static int __init init_transition_pgtable(pgd_t *pgd)
> +{
> +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> +	unsigned long vaddr, paddr;
> +	int result = -ENOMEM;
> +	p4d_t *p4d;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +
> +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> +	pgd += pgd_index(vaddr);
> +	if (!pgd_present(*pgd)) {
> +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> +		if (!p4d)
> +			goto err;

        return -ENOMEM?

the error labels is pretty silly without an actual cleanup, right?

> +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> +	}
> +	p4d = p4d_offset(pgd, vaddr);
> +	if (!p4d_present(*p4d)) {
> +		pud = (pud_t *)alloc_pgt_page(NULL);
> +		if (!pud)
> +			goto err;

Ditto. But what mops up the already allocated page above?
> +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> +
> +	return 0;
> +err:
> +	return result;
> +}

Can you please move that function to the place where it is used?

> +
> +static void acpi_mp_play_dead(void)
> +{
> +	play_dead_common();
> +	asm_acpi_mp_play_dead();
> +}
> +
> +static void acpi_mp_cpu_die(unsigned int cpu)
> +{
> +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);

u32 apicid

> +	unsigned long timeout;
> +
> +	/*
> +	 * Use TEST mailbox command to prove that BIOS got control over
> +	 * the CPU before declaring it dead.
> +	 *
> +	 * BIOS has to clear 'command' field of the mailbox.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id = apicid;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_TEST);
> +
> +	/* Don't wait longer than a second. */
> +	timeout = USEC_PER_SEC;
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> +		udelay(1);
> +}
> +
> +static void acpi_mp_stop_other_cpus(int wait)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());

This clearly was never tested with lockdep. At the point where
stop_other_cpus() is invoked the invoking CPU has interrupts disabled...

> +}
> +
> +static void acpi_mp_crash_stop_other_cpus(void)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());

Yuck. Crash can happen at arbitrary places. So you really cannot invoke
the whole CPU hotplug state machine from here.

There is a reason why the other implementation just kick CPUs into some
"safe" state.

> +	/* The kernel is broken so disable interrupts */
> +	local_irq_disable();
> +}
> +
> +static int __init acpi_mp_setup_reset(u64 reset_vector)
> +{
> +	pgd_t *pgd;
> +	struct x86_mapping_info info = {
> +		.alloc_pgt_page = alloc_pgt_page,
> +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> +	};
> +
> +	pgd = alloc_pgt_page(NULL);
> +
> +	for (int i = 0; i < nr_pfn_mapped; i++) {
> +		unsigned long mstart, mend;

Missing newline

> +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> +			return -ENOMEM;
> +	}
> +
> +	if (kernel_ident_mapping_init(&info, pgd,
> +				      PAGE_ALIGN_DOWN(reset_vector),
> +				      PAGE_ALIGN(reset_vector + 1))) {
> +		return -ENOMEM;
> +	}
> +
> +	if (init_transition_pgtable(pgd))
> +		return -ENOMEM;
> +
> +	smp_ops.play_dead = acpi_mp_play_dead;
> +	smp_ops.cpu_die = acpi_mp_cpu_die;
> +	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
> +	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
> +
> +	acpi_mp_reset_vector_paddr = reset_vector;
> +	acpi_mp_pgd = __pa(pgd);
> +
> +	return 0;
> +}
> +
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
>  	if (!acpi_mp_wake_mailbox_paddr) {
> @@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	struct acpi_madt_multiproc_wakeup *mp_wake;
>  
>  	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> +	if (!mp_wake)
> +		return -EINVAL;
> +
> +	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
> +		return -EINVAL;
> +	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
>  		return -EINVAL;
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
>  	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
> -	cpu_hotplug_disable_offlining();
> +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> +		acpi_mp_setup_reset(mp_wake->reset_vector);
> +	} else {
> +		cpu_hotplug_disable_offlining();
>  
> -	/*
> -	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> -	 * It limits kexec: the second kernel won't be able to use more than
> -	 * one CPU.
> -	 *
> -	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> -	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> -	 *
> -	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> -	 * indicate that the mailbox is not usable.  This prevents the
> -	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> -	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> -	 *
> -	 * This is Linux-specific protocol and not reflected in ACPI spec.
> -	 */
> -	mp_wake->mailbox_address = 0;
> +		/*
> +		 * ACPI MADT doesn't allow to offline CPU after it got woke up.

This is not longer accurate as V1 allows that ....

> +		 * It limits kexec: the second kernel won't be able to use more
> +		 * than one CPU.

Thanks,

        tglx

Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Thomas Gleixner]

On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:

> MADT Multiprocessor Wakeup structure version 1 brings support of CPU
> offlining: BIOS provides a reset vector where the CPU has to jump to
> offline itself. The new TEST mailbox command can be used to test the CPU
> offlined successfully and BIOS has control over it.
>
> Add CPU offling support for ACPI MADT wakeup method by implementing
> custom cpu_die, play_dead and stop_other_cpus SMP operations.
>
> CPU offlining makes possible to hand over secondary CPUs over kexec, not

makes it possible

> limiting the second kernel with single CPU.

s/with/to/

> The change conforms to the approved ACPI spec change proposal. See the
> +SYM_FUNC_START(asm_acpi_mp_play_dead)
> +	/* Load address of reset vector into RCX to jump when kernel is ready */
> +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> +
> +	/* Turn off global entries. Following CR3 write will flush them. */
> +	movq	%cr4, %rdx
> +	andq	$~(X86_CR4_PGE), %rdx
> +	movq	%rdx, %cr4
> +
> +	/* Switch to identity mapping */
> +	movq	acpi_mp_pgd(%rip), %rax
> +	movq	%rax, %cr3

You can just make this function:

    asm_acpi_mp_play_dead(u64 reset_vector, u64 pgd_pa);

then you have the reset vector in RDI and the pgd in RSI and spare the
global variables.

>  
>  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
>  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
>  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
>  
> +u64 acpi_mp_pgd;
> +u64 acpi_mp_reset_vector_paddr;

See above (static) and __ro_after_init please

> +
> +void asm_acpi_mp_play_dead(void);
> +
> +static void __init *alloc_pgt_page(void *context)
> +{

What's the purpose of the context argument?

> +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> +}
> +
> +/*
> + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> + * the same place as in the kernel page tables. The function switches to
> + * the identity mapping and has be present at the same spot in before and
> + * after transition.

Why does it need to be there after the CPU jumped to the reset vector?

> + */
> +static int __init init_transition_pgtable(pgd_t *pgd)
> +{
> +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> +	unsigned long vaddr, paddr;
> +	int result = -ENOMEM;
> +	p4d_t *p4d;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *pte;
> +
> +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> +	pgd += pgd_index(vaddr);
> +	if (!pgd_present(*pgd)) {
> +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> +		if (!p4d)
> +			goto err;

        return -ENOMEM?

the error labels is pretty silly without an actual cleanup, right?

> +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> +	}
> +	p4d = p4d_offset(pgd, vaddr);
> +	if (!p4d_present(*p4d)) {
> +		pud = (pud_t *)alloc_pgt_page(NULL);
> +		if (!pud)
> +			goto err;

Ditto. But what mops up the already allocated page above?
> +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> +
> +	return 0;
> +err:
> +	return result;
> +}

Can you please move that function to the place where it is used?

> +
> +static void acpi_mp_play_dead(void)
> +{
> +	play_dead_common();
> +	asm_acpi_mp_play_dead();
> +}
> +
> +static void acpi_mp_cpu_die(unsigned int cpu)
> +{
> +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);

u32 apicid

> +	unsigned long timeout;
> +
> +	/*
> +	 * Use TEST mailbox command to prove that BIOS got control over
> +	 * the CPU before declaring it dead.
> +	 *
> +	 * BIOS has to clear 'command' field of the mailbox.
> +	 */
> +	acpi_mp_wake_mailbox->apic_id = apicid;
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_TEST);
> +
> +	/* Don't wait longer than a second. */
> +	timeout = USEC_PER_SEC;
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> +		udelay(1);
> +}
> +
> +static void acpi_mp_stop_other_cpus(int wait)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());

This clearly was never tested with lockdep. At the point where
stop_other_cpus() is invoked the invoking CPU has interrupts disabled...

> +}
> +
> +static void acpi_mp_crash_stop_other_cpus(void)
> +{
> +	smp_shutdown_nonboot_cpus(smp_processor_id());

Yuck. Crash can happen at arbitrary places. So you really cannot invoke
the whole CPU hotplug state machine from here.

There is a reason why the other implementation just kick CPUs into some
"safe" state.

> +	/* The kernel is broken so disable interrupts */
> +	local_irq_disable();
> +}
> +
> +static int __init acpi_mp_setup_reset(u64 reset_vector)
> +{
> +	pgd_t *pgd;
> +	struct x86_mapping_info info = {
> +		.alloc_pgt_page = alloc_pgt_page,
> +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> +	};
> +
> +	pgd = alloc_pgt_page(NULL);
> +
> +	for (int i = 0; i < nr_pfn_mapped; i++) {
> +		unsigned long mstart, mend;

Missing newline

> +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> +			return -ENOMEM;
> +	}
> +
> +	if (kernel_ident_mapping_init(&info, pgd,
> +				      PAGE_ALIGN_DOWN(reset_vector),
> +				      PAGE_ALIGN(reset_vector + 1))) {
> +		return -ENOMEM;
> +	}
> +
> +	if (init_transition_pgtable(pgd))
> +		return -ENOMEM;
> +
> +	smp_ops.play_dead = acpi_mp_play_dead;
> +	smp_ops.cpu_die = acpi_mp_cpu_die;
> +	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
> +	smp_ops.crash_stop_other_cpus = acpi_mp_crash_stop_other_cpus;
> +
> +	acpi_mp_reset_vector_paddr = reset_vector;
> +	acpi_mp_pgd = __pa(pgd);
> +
> +	return 0;
> +}
> +
>  static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
>  {
>  	if (!acpi_mp_wake_mailbox_paddr) {
> @@ -74,31 +223,43 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  	struct acpi_madt_multiproc_wakeup *mp_wake;
>  
>  	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> -	if (BAD_MADT_ENTRY(mp_wake, end))
> +	if (!mp_wake)
> +		return -EINVAL;
> +
> +	if (end - (unsigned long)mp_wake < ACPI_MADT_MP_WAKEUP_SIZE_V0)
> +		return -EINVAL;
> +	if (mp_wake->header.length < ACPI_MADT_MP_WAKEUP_SIZE_V0)
>  		return -EINVAL;
>  
>  	acpi_table_print_madt_entry(&header->common);
>  
>  	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
>  
> -	cpu_hotplug_disable_offlining();
> +	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
> +	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
> +		acpi_mp_setup_reset(mp_wake->reset_vector);
> +	} else {
> +		cpu_hotplug_disable_offlining();
>  
> -	/*
> -	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> -	 * It limits kexec: the second kernel won't be able to use more than
> -	 * one CPU.
> -	 *
> -	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> -	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> -	 *
> -	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> -	 * indicate that the mailbox is not usable.  This prevents the
> -	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> -	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> -	 *
> -	 * This is Linux-specific protocol and not reflected in ACPI spec.
> -	 */
> -	mp_wake->mailbox_address = 0;
> +		/*
> +		 * ACPI MADT doesn't allow to offline CPU after it got woke up.

This is not longer accurate as V1 allows that ....

> +		 * It limits kexec: the second kernel won't be able to use more
> +		 * than one CPU.

Thanks,

        tglx

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Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Kirill A. Shutemov]

On Sun, Oct 29, 2023 at 06:31:36PM +0100, Thomas Gleixner wrote:
> On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:
> 
> > MADT Multiprocessor Wakeup structure version 1 brings support of CPU
> > offlining: BIOS provides a reset vector where the CPU has to jump to
> > offline itself. The new TEST mailbox command can be used to test the CPU
> > offlined successfully and BIOS has control over it.
> >
> > Add CPU offling support for ACPI MADT wakeup method by implementing
> > custom cpu_die, play_dead and stop_other_cpus SMP operations.
> >
> > CPU offlining makes possible to hand over secondary CPUs over kexec, not
> 
> makes it possible
> 
> > limiting the second kernel with single CPU.
> 
> s/with/to/

Okay.

> > The change conforms to the approved ACPI spec change proposal. See the
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> 
> You can just make this function:
> 
>     asm_acpi_mp_play_dead(u64 reset_vector, u64 pgd_pa);
> 
> then you have the reset vector in RDI and the pgd in RSI and spare the
> global variables.

Yeah, it is better. Thanks.

> >  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> > @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
> >  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> >  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> > +u64 acpi_mp_pgd;
> > +u64 acpi_mp_reset_vector_paddr;
> 
> See above (static) and __ro_after_init please
> 
> > +
> > +void asm_acpi_mp_play_dead(void);
> > +
> > +static void __init *alloc_pgt_page(void *context)
> > +{
> 
> What's the purpose of the context argument?

To conform to x86_mapping_info::alloc_pgt_page type.

I will rename the argument to 'dummy' and add comment.

> > +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +}
> > +
> > +/*
> > + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> > + * the same place as in the kernel page tables. The function switches to
> > + * the identity mapping and has be present at the same spot in before and
> > + * after transition.
> 
> Why does it need to be there after the CPU jumped to the reset vector?

After transition to the identity mapping, not after jumping to reset
vector. I will adjust the comment.

> > + */
> > +static int __init init_transition_pgtable(pgd_t *pgd)
> > +{
> > +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> > +	unsigned long vaddr, paddr;
> > +	int result = -ENOMEM;
> > +	p4d_t *p4d;
> > +	pud_t *pud;
> > +	pmd_t *pmd;
> > +	pte_t *pte;
> > +
> > +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> > +	pgd += pgd_index(vaddr);
> > +	if (!pgd_present(*pgd)) {
> > +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> > +		if (!p4d)
> > +			goto err;
> 
>         return -ENOMEM?
> 
> the error labels is pretty silly without an actual cleanup, right?

Right.

> > +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> > +	}
> > +	p4d = p4d_offset(pgd, vaddr);
> > +	if (!p4d_present(*p4d)) {
> > +		pud = (pud_t *)alloc_pgt_page(NULL);
> > +		if (!pud)
> > +			goto err;
> 
> Ditto. But what mops up the already allocated page above?

Oops. I will add cleanup in acpi_mp_setup_reset() if
kernel_ident_mapping_init() or init_transition_pgtable() fails.

> > +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> > +
> > +	return 0;
> > +err:
> > +	return result;
> > +}
> 
> Can you please move that function to the place where it is used?

Sure.

> > +
> > +static void acpi_mp_play_dead(void)
> > +{
> > +	play_dead_common();
> > +	asm_acpi_mp_play_dead();
> > +}
> > +
> > +static void acpi_mp_cpu_die(unsigned int cpu)
> > +{
> > +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
> 
> u32 apicid

Okay.

> > +	unsigned long timeout;
> > +
> > +	/*
> > +	 * Use TEST mailbox command to prove that BIOS got control over
> > +	 * the CPU before declaring it dead.
> > +	 *
> > +	 * BIOS has to clear 'command' field of the mailbox.
> > +	 */
> > +	acpi_mp_wake_mailbox->apic_id = apicid;
> > +	smp_store_release(&acpi_mp_wake_mailbox->command,
> > +			  ACPI_MP_WAKE_COMMAND_TEST);
> > +
> > +	/* Don't wait longer than a second. */
> > +	timeout = USEC_PER_SEC;
> > +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> > +		udelay(1);
> > +}
> > +
> > +static void acpi_mp_stop_other_cpus(int wait)
> > +{
> > +	smp_shutdown_nonboot_cpus(smp_processor_id());
> 
> This clearly was never tested with lockdep. At the point where
> stop_other_cpus() is invoked the invoking CPU has interrupts disabled...

Hm. I do have lockdep enabled and there's no reported.

And I am not sure why it should complain. At this point we are running on
reboot cpu (after migrate_to_reboot_cpu()).

Could you elaborate on what the problem here?

> > +}
> > +
> > +static void acpi_mp_crash_stop_other_cpus(void)
> > +{
> > +	smp_shutdown_nonboot_cpus(smp_processor_id());
> 
> Yuck. Crash can happen at arbitrary places. So you really cannot invoke
> the whole CPU hotplug state machine from here.
> 
> There is a reason why the other implementation just kick CPUs into some
> "safe" state.

Yeah, fair enough.

What about the implementation below? It is heavily inspired by
nmi_shootdown_cpus().

BTW, I don't understand why nmi_shootdown_cpus() needs 'crashing_cpu' if
it uses apic_send_IPI_allbutself(). 'crashing_cpu' == self, no?


static atomic_t waiting_for_crash_ipi;
static bool crash_ipi_issued;

static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
{
	local_irq_disable();

	crash_save_cpu(regs, raw_smp_processor_id());

	cpu_emergency_stop_pt();

	disable_local_APIC();

	/*
	 * Prepare the CPU for reboot _after_ invoking the callback so that the
	 * callback can safely use virtualization instructions, e.g. VMCLEAR.
	 */
	cpu_emergency_disable_virtualization();

	atomic_dec(&waiting_for_crash_ipi);

	asm_acpi_mp_play_dead(acpi_mp_reset_vector_paddr,
			      acpi_mp_pgd);

	return NMI_HANDLED;
}

static void acpi_mp_crash_stop_other_cpus(void)
{
	unsigned long timeout;

	/* The kernel is broken so disable interrupts */
	local_irq_disable();

	/*
	 * Avoid certain doom if a shootdown already occurred; re-registering
	 * the NMI handler will cause list corruption, modifying the callback
	 * will do who knows what, etc...
	 */
	if (WARN_ON_ONCE(crash_ipi_issued))
		return;

	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);

	/* Would it be better to replace the trap vector here? */
	if (register_nmi_handler(NMI_LOCAL, crash_nmi_callback,
				 NMI_FLAG_FIRST, "crash"))
		return;		/* Return what? */

	apic_send_IPI_allbutself(NMI_VECTOR);

	WRITE_ONCE(crash_ipi_issued, 1);

	/* Don't wait longer than a second. */
	timeout = USEC_PER_SEC;
	while (atomic_read(&waiting_for_crash_ipi) && timeout--)
		udelay(1);
}

> > +	/* The kernel is broken so disable interrupts */
> > +	local_irq_disable();
> > +}
> > +
> > +static int __init acpi_mp_setup_reset(u64 reset_vector)
> > +{
> > +	pgd_t *pgd;
> > +	struct x86_mapping_info info = {
> > +		.alloc_pgt_page = alloc_pgt_page,
> > +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> > +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> > +	};
> > +
> > +	pgd = alloc_pgt_page(NULL);
> > +
> > +	for (int i = 0; i < nr_pfn_mapped; i++) {
> > +		unsigned long mstart, mend;
> 
> Missing newline
> 

Okay.

> >  
> > -	/*
> > -	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> > -	 * It limits kexec: the second kernel won't be able to use more than
> > -	 * one CPU.
> > -	 *
> > -	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> > -	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> > -	 *
> > -	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> > -	 * indicate that the mailbox is not usable.  This prevents the
> > -	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> > -	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> > -	 *
> > -	 * This is Linux-specific protocol and not reflected in ACPI spec.
> > -	 */
> > -	mp_wake->mailbox_address = 0;
> > +		/*
> > +		 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> This is not longer accurate as V1 allows that ....
> 

Will fix.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Kirill A. Shutemov]

On Sun, Oct 29, 2023 at 06:31:36PM +0100, Thomas Gleixner wrote:
> On Fri, Oct 20 2023 at 18:12, Kirill A. Shutemov wrote:
> 
> > MADT Multiprocessor Wakeup structure version 1 brings support of CPU
> > offlining: BIOS provides a reset vector where the CPU has to jump to
> > offline itself. The new TEST mailbox command can be used to test the CPU
> > offlined successfully and BIOS has control over it.
> >
> > Add CPU offling support for ACPI MADT wakeup method by implementing
> > custom cpu_die, play_dead and stop_other_cpus SMP operations.
> >
> > CPU offlining makes possible to hand over secondary CPUs over kexec, not
> 
> makes it possible
> 
> > limiting the second kernel with single CPU.
> 
> s/with/to/

Okay.

> > The change conforms to the approved ACPI spec change proposal. See the
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> 
> You can just make this function:
> 
>     asm_acpi_mp_play_dead(u64 reset_vector, u64 pgd_pa);
> 
> then you have the reset vector in RDI and the pgd in RSI and spare the
> global variables.

Yeah, it is better. Thanks.

> >  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> > @@ -11,6 +16,150 @@ static u64 acpi_mp_wake_mailbox_paddr;
> >  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> >  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> > +u64 acpi_mp_pgd;
> > +u64 acpi_mp_reset_vector_paddr;
> 
> See above (static) and __ro_after_init please
> 
> > +
> > +void asm_acpi_mp_play_dead(void);
> > +
> > +static void __init *alloc_pgt_page(void *context)
> > +{
> 
> What's the purpose of the context argument?

To conform to x86_mapping_info::alloc_pgt_page type.

I will rename the argument to 'dummy' and add comment.

> > +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +}
> > +
> > +/*
> > + * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
> > + * the same place as in the kernel page tables. The function switches to
> > + * the identity mapping and has be present at the same spot in before and
> > + * after transition.
> 
> Why does it need to be there after the CPU jumped to the reset vector?

After transition to the identity mapping, not after jumping to reset
vector. I will adjust the comment.

> > + */
> > +static int __init init_transition_pgtable(pgd_t *pgd)
> > +{
> > +	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> > +	unsigned long vaddr, paddr;
> > +	int result = -ENOMEM;
> > +	p4d_t *p4d;
> > +	pud_t *pud;
> > +	pmd_t *pmd;
> > +	pte_t *pte;
> > +
> > +	vaddr = (unsigned long)asm_acpi_mp_play_dead;
> > +	pgd += pgd_index(vaddr);
> > +	if (!pgd_present(*pgd)) {
> > +		p4d = (p4d_t *)alloc_pgt_page(NULL);
> > +		if (!p4d)
> > +			goto err;
> 
>         return -ENOMEM?
> 
> the error labels is pretty silly without an actual cleanup, right?

Right.

> > +		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
> > +	}
> > +	p4d = p4d_offset(pgd, vaddr);
> > +	if (!p4d_present(*p4d)) {
> > +		pud = (pud_t *)alloc_pgt_page(NULL);
> > +		if (!pud)
> > +			goto err;
> 
> Ditto. But what mops up the already allocated page above?

Oops. I will add cleanup in acpi_mp_setup_reset() if
kernel_ident_mapping_init() or init_transition_pgtable() fails.

> > +	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
> > +
> > +	return 0;
> > +err:
> > +	return result;
> > +}
> 
> Can you please move that function to the place where it is used?

Sure.

> > +
> > +static void acpi_mp_play_dead(void)
> > +{
> > +	play_dead_common();
> > +	asm_acpi_mp_play_dead();
> > +}
> > +
> > +static void acpi_mp_cpu_die(unsigned int cpu)
> > +{
> > +	int apicid = per_cpu(x86_cpu_to_apicid, cpu);
> 
> u32 apicid

Okay.

> > +	unsigned long timeout;
> > +
> > +	/*
> > +	 * Use TEST mailbox command to prove that BIOS got control over
> > +	 * the CPU before declaring it dead.
> > +	 *
> > +	 * BIOS has to clear 'command' field of the mailbox.
> > +	 */
> > +	acpi_mp_wake_mailbox->apic_id = apicid;
> > +	smp_store_release(&acpi_mp_wake_mailbox->command,
> > +			  ACPI_MP_WAKE_COMMAND_TEST);
> > +
> > +	/* Don't wait longer than a second. */
> > +	timeout = USEC_PER_SEC;
> > +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> > +		udelay(1);
> > +}
> > +
> > +static void acpi_mp_stop_other_cpus(int wait)
> > +{
> > +	smp_shutdown_nonboot_cpus(smp_processor_id());
> 
> This clearly was never tested with lockdep. At the point where
> stop_other_cpus() is invoked the invoking CPU has interrupts disabled...

Hm. I do have lockdep enabled and there's no reported.

And I am not sure why it should complain. At this point we are running on
reboot cpu (after migrate_to_reboot_cpu()).

Could you elaborate on what the problem here?

> > +}
> > +
> > +static void acpi_mp_crash_stop_other_cpus(void)
> > +{
> > +	smp_shutdown_nonboot_cpus(smp_processor_id());
> 
> Yuck. Crash can happen at arbitrary places. So you really cannot invoke
> the whole CPU hotplug state machine from here.
> 
> There is a reason why the other implementation just kick CPUs into some
> "safe" state.

Yeah, fair enough.

What about the implementation below? It is heavily inspired by
nmi_shootdown_cpus().

BTW, I don't understand why nmi_shootdown_cpus() needs 'crashing_cpu' if
it uses apic_send_IPI_allbutself(). 'crashing_cpu' == self, no?


static atomic_t waiting_for_crash_ipi;
static bool crash_ipi_issued;

static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
{
	local_irq_disable();

	crash_save_cpu(regs, raw_smp_processor_id());

	cpu_emergency_stop_pt();

	disable_local_APIC();

	/*
	 * Prepare the CPU for reboot _after_ invoking the callback so that the
	 * callback can safely use virtualization instructions, e.g. VMCLEAR.
	 */
	cpu_emergency_disable_virtualization();

	atomic_dec(&waiting_for_crash_ipi);

	asm_acpi_mp_play_dead(acpi_mp_reset_vector_paddr,
			      acpi_mp_pgd);

	return NMI_HANDLED;
}

static void acpi_mp_crash_stop_other_cpus(void)
{
	unsigned long timeout;

	/* The kernel is broken so disable interrupts */
	local_irq_disable();

	/*
	 * Avoid certain doom if a shootdown already occurred; re-registering
	 * the NMI handler will cause list corruption, modifying the callback
	 * will do who knows what, etc...
	 */
	if (WARN_ON_ONCE(crash_ipi_issued))
		return;

	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);

	/* Would it be better to replace the trap vector here? */
	if (register_nmi_handler(NMI_LOCAL, crash_nmi_callback,
				 NMI_FLAG_FIRST, "crash"))
		return;		/* Return what? */

	apic_send_IPI_allbutself(NMI_VECTOR);

	WRITE_ONCE(crash_ipi_issued, 1);

	/* Don't wait longer than a second. */
	timeout = USEC_PER_SEC;
	while (atomic_read(&waiting_for_crash_ipi) && timeout--)
		udelay(1);
}

> > +	/* The kernel is broken so disable interrupts */
> > +	local_irq_disable();
> > +}
> > +
> > +static int __init acpi_mp_setup_reset(u64 reset_vector)
> > +{
> > +	pgd_t *pgd;
> > +	struct x86_mapping_info info = {
> > +		.alloc_pgt_page = alloc_pgt_page,
> > +		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
> > +		.kernpg_flag    = _KERNPG_TABLE_NOENC,
> > +	};
> > +
> > +	pgd = alloc_pgt_page(NULL);
> > +
> > +	for (int i = 0; i < nr_pfn_mapped; i++) {
> > +		unsigned long mstart, mend;
> 
> Missing newline
> 

Okay.

> >  
> > -	/*
> > -	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> > -	 * It limits kexec: the second kernel won't be able to use more than
> > -	 * one CPU.
> > -	 *
> > -	 * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> > -	 * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
> > -	 *
> > -	 * Zero out mailbox address in the ACPI MADT wakeup structure to
> > -	 * indicate that the mailbox is not usable.  This prevents the
> > -	 * kexec()-ed kernel from reading a vaild mailbox, which in turn
> > -	 * makes the kexec()-ed kernel only be able to use the boot CPU.
> > -	 *
> > -	 * This is Linux-specific protocol and not reflected in ACPI spec.
> > -	 */
> > -	mp_wake->mailbox_address = 0;
> > +		/*
> > +		 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> 
> This is not longer accurate as V1 allows that ....
> 

Will fix.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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