[PATCHv8 04/17] cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

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

Currently CPU hotplug is 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>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 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 d07be9d05cd0..19614302e0c4 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 cf79ea6f3007..d222be8d7a07 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 #include <linux/acpi.h>
+#include <linux/cpu.h>
 #include <linux/io.h>
 #include <asm/apic.h>
 #include <asm/barrier.h>
@@ -76,6 +77,8 @@ 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 ac6af196c6f5..dde8e8472897 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1531,8 +1531,7 @@ 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;
-- 
2.43.0