[PATCH v6 00/16] ACPI/arm64: add support for virtual cpu hotplug

[PATCH v6 00/16] ACPI/arm64: add support for virtual cpu hotplug

[Jonathan Cameron]

Fundamental change: At the level of common ACPI infrastructure, use
the existing hotplug path for arm64 even though what needs to be
done at the architecture specific level is quite different.

An explicit check in arch_register_cpu() for arm64 prevents
this code doing anything if Physical CPU Hotplug is signalled.

This should resolve any concerns about treating virtual CPU
hotplug as if it were physical and potential unwanted side effects
if physical CPU hotplug is added to the ARM architecture in the
future.

v6: Thanks to Rafael for extensive help with the approach + reviews.
Specific changes:
 - Do not differentiate wrt code flow between traditional CPU HP
   and the new ARM flow.  The conditions on performing hotplug actions
   do need to be adjusted though to incorporate the slightly different
   state transition
     Added PRESENT + !ENABLED -> PRESENT + ENABLED
     to existing !PRESENT + !ENABLED -> PRESENT + ENABLED
 - Enable ACPI_HOTPLUG_CPU on arm64 and drop the earlier patches that
   took various code out of the protection of that.  Now the paths
 - New patch to drop unnecessary _STA check in hotplug code. This
   code cannot be entered unless ENABLED + PRESENT are set.
 - New patch to unify the flow of already onlined (at time of driver
   load) and hotplugged CPUs in acpi/processor_driver.c.
   This change is necessary because we can't easily distinguish the
   2 cases of deferred vs hotplug calls of register_cpu() on arm64.
   It is also a nice simplification.
 - Use flags rather than a structure for the extra parameter to
   acpi_scan_check_and_detach() - Thank to Shameer for offline feedback.

Updated version of James' original introduction.

This series adds what looks like cpuhotplug support to arm64 for use in
virtual machines. It does this by moving the cpu_register() calls for
architectures that support ACPI into an arch specific call made from
the ACPI processor driver.
 
The kubernetes folk really want to be able to add CPUs to an existing VM,
in exactly the same way they do on x86. The use-case is pre-booting guests
with one CPU, then adding the number that were actually needed when the
workload is provisioned.

Wait? Doesn't arm64 support cpuhotplug already!?
In the arm world, cpuhotplug gets used to mean removing the power from a CPU.
The CPU is offline, and remains present. For x86, and ACPI, cpuhotplug
has the additional step of physically removing the CPU, so that it isn't
present anymore.
 
Arm64 doesn't support this, and can't support it: CPUs are really a slice
of the SoC, and there is not enough information in the existing ACPI tables
to describe which bits of the slice also got removed. Without a reference
machine: adding this support to the spec is a wild goose chase.
 
Critically: everything described in the firmware tables must remain present.
 
For a virtual machine this is easy as all the other bits of 'virtual SoC'
are emulated, so they can (and do) remain present when a vCPU is 'removed'.

On a system that supports cpuhotplug the MADT has to describe every possible
CPU at boot. Under KVM, the vGIC needs to know about every possible vCPU before
the guest is started.
With these constraints, virtual-cpuhotplug is really just a hypervisor/firmware
policy about which CPUs can be brought online.
 
This series adds support for virtual-cpuhotplug as exactly that: firmware
policy. This may even work on a physical machine too; for a guest the part of
firmware is played by the VMM. (typically Qemu).
 
PSCI support is modified to return 'DENIED' if the CPU can't be brought
online/enabled yet. The CPU object's _STA method's enabled bit is used to
indicate firmware's current disposition. If the CPU has its enabled bit clear,
it will not be registered with sysfs, and attempts to bring it online will
fail. The notifications that _STA has changed its value then work in the same
way as physical hotplug, and firmware can cause the CPU to be registered some
time later, allowing it to be brought online.
 
This creates something that looks like cpuhotplug to user-space and the
kernel beyond arm64 architecture specific code, as the sysfs
files appear and disappear, and the udev notifications look the same.
 
One notable difference is the CPU present mask, which is exposed via sysfs.
Because the CPUs remain present throughout, they can still be seen in that mask.
This value does get used by webbrowsers to estimate the number of CPUs
as the CPU online mask is constantly changed on mobile phones.
 
Linux is tolerant of PSCI returning errors, as its always been allowed to do
that. To avoid confusing OS that can't tolerate this, we needed an additional
bit in the MADT GICC flags. This series copies ACPI_MADT_ONLINE_CAPABLE, which
appears to be for this purpose, but calls it ACPI_MADT_GICC_CPU_CAPABLE as it
has a different bit position in the GICC.
 
This code is unconditionally enabled for all ACPI architectures, though for
now only arm64 will have deferred the cpu_register() calls.

If folk want to play along at home, you'll need a copy of Qemu that supports this.
https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v2

Replace your '-smp' argument with something like:
 | -smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
 
 then feed the following to the Qemu montior;
 | (qemu) device_add driver=host-arm-cpu,core-id=1,id=cpu1
 | (qemu) device_del cpu1

James Morse (7):
  ACPI: processor: Register deferred CPUs from acpi_processor_get_info()
  ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug
  arm64: acpi: Move get_cpu_for_acpi_id() to a header
  irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc()
  irqchip/gic-v3: Add support for ACPI's disabled but 'online capable'
    CPUs
  arm64: document virtual CPU hotplug's expectations
  cpumask: Add enabled cpumask for present CPUs that can be brought
    online

Jean-Philippe Brucker (1):
  arm64: psci: Ignore DENIED CPUs

Jonathan Cameron (8):
  ACPI: processor: Simplify initial onlining to use same path for cold
    and hotplug
  cpu: Do not warn on arch_register_cpu() returning -EPROBE_DEFER
  ACPI: processor: Drop duplicated check on _STA (enabled + present)
  ACPI: processor: Move checks and availability of acpi_processor
    earlier
  ACPI: processor: Add acpi_get_processor_handle() helper
  ACPI: scan: switch to flags for acpi_scan_check_and_detach();
  arm64: arch_register_cpu() variant to check if an ACPI handle is now
    available.
  arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is
    enabled.

 .../ABI/testing/sysfs-devices-system-cpu      |   6 +
 Documentation/arch/arm64/cpu-hotplug.rst      |  79 ++++++++++++
 Documentation/arch/arm64/index.rst            |   1 +
 arch/arm64/Kconfig                            |   1 +
 arch/arm64/include/asm/acpi.h                 |  11 ++
 arch/arm64/kernel/acpi.c                      |  16 +++
 arch/arm64/kernel/acpi_numa.c                 |  11 --
 arch/arm64/kernel/psci.c                      |   2 +-
 arch/arm64/kernel/smp.c                       |  56 ++++++++-
 drivers/acpi/acpi_processor.c                 | 112 +++++++++++-------
 drivers/acpi/processor_driver.c               |  44 ++-----
 drivers/acpi/scan.c                           |  47 ++++++--
 drivers/base/cpu.c                            |  12 +-
 drivers/irqchip/irq-gic-v3.c                  |  32 +++--
 include/acpi/acpi_bus.h                       |   1 +
 include/acpi/processor.h                      |   2 +-
 include/linux/acpi.h                          |  10 +-
 include/linux/cpumask.h                       |  25 ++++
 kernel/cpu.c                                  |   3 +
 19 files changed, 362 insertions(+), 109 deletions(-)
 create mode 100644 Documentation/arch/arm64/cpu-hotplug.rst

-- 
2.39.2

[PATCH v6 01/16] ACPI: processor: Simplify initial onlining to use same path for cold and hotplug

[Jonathan Cameron]

Separate code paths, combined with a flag set in acpi_processor.c to
indicate a struct acpi_processor was for a hotplugged CPU ensured that
per CPU data was only set up the first time that a CPU was initialized.
This appears to be unnecessary as the paths can be combined by letting
the online logic also handle any CPUs online at the time of driver load.

Motivation for this change, beyond simplification, is that ARM64
virtual CPU HP uses the same code paths for hotplug and cold path in
acpi_processor.c so had no easy way to set the flag for hotplug only.
Removing this necessity will enable ARM64 vCPU HP to reuse the existing
code paths.

Leave noisy pr_info() in place but update it to not state the CPU
was hotplugged.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v6: New patch.
RFT: I have very limited test resources for x86 and other
architectures that may be affected by this change.
---
 drivers/acpi/acpi_processor.c   |  1 -
 drivers/acpi/processor_driver.c | 44 ++++++++++-----------------------
 include/acpi/processor.h        |  2 +-
 3 files changed, 14 insertions(+), 33 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 7a0dd35d62c9..7fc924aeeed0 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -216,7 +216,6 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 	 * gets online for the first time.
 	 */
 	pr_info("CPU%d has been hot-added\n", pr->id);
-	pr->flags.need_hotplug_init = 1;
 
 out:
 	cpus_write_unlock();
diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index 67db60eda370..55782eac3ff1 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -33,7 +33,6 @@ MODULE_AUTHOR("Paul Diefenbaugh");
 MODULE_DESCRIPTION("ACPI Processor Driver");
 MODULE_LICENSE("GPL");
 
-static int acpi_processor_start(struct device *dev);
 static int acpi_processor_stop(struct device *dev);
 
 static const struct acpi_device_id processor_device_ids[] = {
@@ -47,7 +46,6 @@ static struct device_driver acpi_processor_driver = {
 	.name = "processor",
 	.bus = &cpu_subsys,
 	.acpi_match_table = processor_device_ids,
-	.probe = acpi_processor_start,
 	.remove = acpi_processor_stop,
 };
 
@@ -115,12 +113,10 @@ static int acpi_soft_cpu_online(unsigned int cpu)
 	 * CPU got physically hotplugged and onlined for the first time:
 	 * Initialize missing things.
 	 */
-	if (pr->flags.need_hotplug_init) {
+	if (!pr->flags.previously_online) {
 		int ret;
 
-		pr_info("Will online and init hotplugged CPU: %d\n",
-			pr->id);
-		pr->flags.need_hotplug_init = 0;
+		pr_info("Will online and init CPU: %d\n", pr->id);
 		ret = __acpi_processor_start(device);
 		WARN(ret, "Failed to start CPU: %d\n", pr->id);
 	} else {
@@ -167,9 +163,6 @@ static int __acpi_processor_start(struct acpi_device *device)
 	if (!pr)
 		return -ENODEV;
 
-	if (pr->flags.need_hotplug_init)
-		return 0;
-
 	result = acpi_cppc_processor_probe(pr);
 	if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
 		dev_dbg(&device->dev, "CPPC data invalid or not present\n");
@@ -185,32 +178,21 @@ static int __acpi_processor_start(struct acpi_device *device)
 
 	status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
 					     acpi_processor_notify, device);
-	if (ACPI_SUCCESS(status))
-		return 0;
+	if (!ACPI_SUCCESS(status)) {
+		result = -ENODEV;
+		goto err_thermal_exit;
+	}
+	pr->flags.previously_online = 1;
 
-	result = -ENODEV;
-	acpi_processor_thermal_exit(pr, device);
+	return 0;
 
+err_thermal_exit:
+	acpi_processor_thermal_exit(pr, device);
 err_power_exit:
 	acpi_processor_power_exit(pr);
 	return result;
 }
 
-static int acpi_processor_start(struct device *dev)
-{
-	struct acpi_device *device = ACPI_COMPANION(dev);
-	int ret;
-
-	if (!device)
-		return -ENODEV;
-
-	/* Protect against concurrent CPU hotplug operations */
-	cpu_hotplug_disable();
-	ret = __acpi_processor_start(device);
-	cpu_hotplug_enable();
-	return ret;
-}
-
 static int acpi_processor_stop(struct device *dev)
 {
 	struct acpi_device *device = ACPI_COMPANION(dev);
@@ -279,9 +261,9 @@ static int __init acpi_processor_driver_init(void)
 	if (result < 0)
 		return result;
 
-	result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
-					   "acpi/cpu-drv:online",
-					   acpi_soft_cpu_online, NULL);
+	result = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+				   "acpi/cpu-drv:online",
+				   acpi_soft_cpu_online, NULL);
 	if (result < 0)
 		goto err;
 	hp_online = result;
diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index 3f34ebb27525..e6f6074eadbf 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -217,7 +217,7 @@ struct acpi_processor_flags {
 	u8 has_lpi:1;
 	u8 power_setup_done:1;
 	u8 bm_rld_set:1;
-	u8 need_hotplug_init:1;
+	u8 previously_online:1;
 };
 
 struct acpi_processor {
-- 
2.39.2

[PATCH v6 02/16] cpu: Do not warn on arch_register_cpu() returning -EPROBE_DEFER

[Jonathan Cameron]

For arm64 the CPU registration cannot complete until the ACPI
interpreter us up and running so in those cases the arch specific
arch_register_cpu() will return -EPROBE_DEFER at this stage and the
registration will be attempted later.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v6: tags
---
 drivers/base/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 56fba44ba391..b9d0d14e5960 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -558,7 +558,7 @@ static void __init cpu_dev_register_generic(void)
 
 	for_each_present_cpu(i) {
 		ret = arch_register_cpu(i);
-		if (ret)
+		if (ret != -EPROBE_DEFER)
 			pr_warn("register_cpu %d failed (%d)\n", i, ret);
 	}
 }
-- 
2.39.2

[PATCH v6 03/16] ACPI: processor: Drop duplicated check on _STA (enabled + present)

[Jonathan Cameron]

The ACPI bus scan will only result in acpi_processor_add() being called
if _STA has already been checked and the result is that the
processor is enabled and present.  Hence drop this additional check.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v6: New patch to drop this unnecessary code. Now I think we only
    need to explicitly read STA to print a warning in the ARM64
    arch_unregister_cpu() path where we want to know if the
    present bit has been unset as well.
---
 drivers/acpi/acpi_processor.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 7fc924aeeed0..ba0a6f0ac841 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -186,17 +186,11 @@ static void __init acpi_pcc_cpufreq_init(void) {}
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 {
-	unsigned long long sta;
-	acpi_status status;
 	int ret;
 
 	if (invalid_phys_cpuid(pr->phys_id))
 		return -ENODEV;
 
-	status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
-	if (ACPI_FAILURE(status) || !(sta & ACPI_STA_DEVICE_PRESENT))
-		return -ENODEV;
-
 	cpu_maps_update_begin();
 	cpus_write_lock();
 
-- 
2.39.2

[PATCH v6 04/16] ACPI: processor: Move checks and availability of acpi_processor earlier

[Jonathan Cameron]

Make the per_cpu(processors, cpu) entries available earlier so that
they are available in arch_register_cpu() as ARM64 will need access
to the acpi_handle to distinguish between acpi_processor_add()
and earlier registration attempts (which will fail as _STA cannot
be checked).

Reorder the remove flow to clear this per_cpu() after
arch_unregister_cpu() has completed, allowing it to be used in
there as well.

Note that on x86 for the CPU hotplug case, the pr->id prior to
acpi_map_cpu() may be invalid. Thus the per_cpu() structures
must be initialized after that call or after checking the ID
is valid (not hotplug path).

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v6: As per discussion in v5 thread, don't use the cpu->dev and
    make this data available earlier by moving the assignment checks
    int acpi_processor_get_info().
---
 drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 32 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index ba0a6f0ac841..2c164451ab53 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -184,7 +184,35 @@ static void __init acpi_pcc_cpufreq_init(void) {}
 
 /* Initialization */
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
-static int acpi_processor_hotadd_init(struct acpi_processor *pr)
+static DEFINE_PER_CPU(void *, processor_device_array);
+
+static void acpi_processor_set_per_cpu(struct acpi_processor *pr,
+				       struct acpi_device *device)
+{
+	BUG_ON(pr->id >= nr_cpu_ids);
+	/*
+	 * Buggy BIOS check.
+	 * ACPI id of processors can be reported wrongly by the BIOS.
+	 * Don't trust it blindly
+	 */
+	if (per_cpu(processor_device_array, pr->id) != NULL &&
+	    per_cpu(processor_device_array, pr->id) != device) {
+		dev_warn(&device->dev,
+			 "BIOS reported wrong ACPI id %d for the processor\n",
+			 pr->id);
+		/* Give up, but do not abort the namespace scan. */
+		return;
+	}
+	/*
+	 * processor_device_array is not cleared on errors to allow buggy BIOS
+	 * checks.
+	 */
+	per_cpu(processor_device_array, pr->id) = device;
+	per_cpu(processors, pr->id) = pr;
+}
+
+static int acpi_processor_hotadd_init(struct acpi_processor *pr,
+				      struct acpi_device *device)
 {
 	int ret;
 
@@ -198,6 +226,8 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 	if (ret)
 		goto out;
 
+	acpi_processor_set_per_cpu(pr, device);
+
 	ret = arch_register_cpu(pr->id);
 	if (ret) {
 		acpi_unmap_cpu(pr->id);
@@ -217,7 +247,8 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 	return ret;
 }
 #else
-static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
+static inline int acpi_processor_hotadd_init(struct acpi_processor *pr,
+					     struct acpi_device *device)
 {
 	return -ENODEV;
 }
@@ -232,6 +263,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
 	acpi_status status = AE_OK;
 	static int cpu0_initialized;
 	unsigned long long value;
+	int ret;
 
 	acpi_processor_errata();
 
@@ -316,10 +348,12 @@ static int acpi_processor_get_info(struct acpi_device *device)
 	 *  because cpuid <-> apicid mapping is persistent now.
 	 */
 	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
-		int ret = acpi_processor_hotadd_init(pr);
+		ret = acpi_processor_hotadd_init(pr, device);
 
 		if (ret)
-			return ret;
+			goto err;
+	} else {
+		acpi_processor_set_per_cpu(pr, device);
 	}
 
 	/*
@@ -357,6 +391,10 @@ static int acpi_processor_get_info(struct acpi_device *device)
 		arch_fix_phys_package_id(pr->id, value);
 
 	return 0;
+
+err:
+	per_cpu(processors, pr->id) = NULL;
+	return ret;
 }
 
 /*
@@ -365,8 +403,6 @@ static int acpi_processor_get_info(struct acpi_device *device)
  * (cpu_data(cpu)) values, like CPU feature flags, family, model, etc.
  * Such things have to be put in and set up by the processor driver's .probe().
  */
-static DEFINE_PER_CPU(void *, processor_device_array);
-
 static int acpi_processor_add(struct acpi_device *device,
 					const struct acpi_device_id *id)
 {
@@ -395,28 +431,6 @@ static int acpi_processor_add(struct acpi_device *device,
 	if (result) /* Processor is not physically present or unavailable */
 		return 0;
 
-	BUG_ON(pr->id >= nr_cpu_ids);
-
-	/*
-	 * Buggy BIOS check.
-	 * ACPI id of processors can be reported wrongly by the BIOS.
-	 * Don't trust it blindly
-	 */
-	if (per_cpu(processor_device_array, pr->id) != NULL &&
-	    per_cpu(processor_device_array, pr->id) != device) {
-		dev_warn(&device->dev,
-			"BIOS reported wrong ACPI id %d for the processor\n",
-			pr->id);
-		/* Give up, but do not abort the namespace scan. */
-		goto err;
-	}
-	/*
-	 * processor_device_array is not cleared on errors to allow buggy BIOS
-	 * checks.
-	 */
-	per_cpu(processor_device_array, pr->id) = device;
-	per_cpu(processors, pr->id) = pr;
-
 	dev = get_cpu_device(pr->id);
 	if (!dev) {
 		result = -ENODEV;
@@ -469,15 +483,16 @@ static void acpi_processor_remove(struct acpi_device *device)
 	device_release_driver(pr->dev);
 	acpi_unbind_one(pr->dev);
 
-	/* Clean up. */
-	per_cpu(processor_device_array, pr->id) = NULL;
-	per_cpu(processors, pr->id) = NULL;
-
 	cpu_maps_update_begin();
 	cpus_write_lock();
 
 	/* Remove the CPU. */
 	arch_unregister_cpu(pr->id);
+
+	/* Clean up. */
+	per_cpu(processor_device_array, pr->id) = NULL;
+	per_cpu(processors, pr->id) = NULL;
+
 	acpi_unmap_cpu(pr->id);
 
 	cpus_write_unlock();
-- 
2.39.2

[PATCH v6 05/16] ACPI: processor: Add acpi_get_processor_handle() helper

[Jonathan Cameron]

If CONFIG_ACPI_PROCESSOR provide a helper to retriever the
acpi_handle for a given CPU allowing access to methods
in DSDT.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v6: New patch
---
 drivers/acpi/acpi_processor.c | 10 ++++++++++
 include/linux/acpi.h          |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 2c164451ab53..7ecb13775d7f 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -35,6 +35,16 @@ EXPORT_PER_CPU_SYMBOL(processors);
 struct acpi_processor_errata errata __read_mostly;
 EXPORT_SYMBOL_GPL(errata);
 
+acpi_handle acpi_get_processor_handle(int cpu)
+{
+	acpi_handle handle = NULL;
+	struct acpi_processor *pr = per_cpu(processors, cpu);;
+
+	if (pr)
+		handle = pr->handle;
+
+	return handle;
+}
 static int acpi_processor_errata_piix4(struct pci_dev *dev)
 {
 	u8 value1 = 0;
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 34829f2c517a..9844a3f9c4e5 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -309,6 +309,8 @@ int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 acpi_id,
 int acpi_unmap_cpu(int cpu);
 #endif /* CONFIG_ACPI_HOTPLUG_CPU */
 
+acpi_handle acpi_get_processor_handle(int cpu);
+
 #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
 int acpi_get_ioapic_id(acpi_handle handle, u32 gsi_base, u64 *phys_addr);
 #endif
@@ -1077,6 +1079,11 @@ static inline bool acpi_sleep_state_supported(u8 sleep_state)
 	return false;
 }
 
+static inline acpi_handle acpi_get_processor_handle(int cpu)
+{
+	return NULL;
+}
+
 #endif	/* !CONFIG_ACPI */
 
 extern void arch_post_acpi_subsys_init(void);
-- 
2.39.2

[PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

The arm64 specific arch_register_cpu() call may defer CPU registration
until the ACPI interpreter is available and the _STA method can
be evaluated.

If this occurs, then a second attempt is made in
acpi_processor_get_info(). Note that the arm64 specific call has
not yet been added so for now this will be called for the original
hotplug case.

For architectures that do not defer until the ACPI Processor
driver loads (e.g. x86), for initially present CPUs there will
already be a CPU device. If present do not try to register again.

Systems can still be booted with 'acpi=off', or not include an
ACPI description at all as in these cases arch_register_cpu()
will not have deferred registration when first called.

This moves the CPU register logic back to a subsys_initcall(),
while the memory nodes will have been registered earlier.
Note this is where the call was prior to the cleanup series so
there should be no side effects of moving it back again for this
specific case.

[PATCH 00/21] Initial cleanups for vCPU HP.
https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/

e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
---
v6: Squash the two paths for conventional CPU Hotplug and arm64
    vCPU HP.
v5: Update commit message to make it clear this is moving the
    init back to where it was until very recently.

    No longer change the condition in the earlier registration point
    as that will be handled by the arm64 registration routine
    deferring until called again here.
---
 drivers/acpi/acpi_processor.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 7ecb13775d7f..0cac77961020 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct acpi_device *device)
 	 *
 	 *  NOTE: Even if the processor has a cpuid, it may not be present
 	 *  because cpuid <-> apicid mapping is persistent now.
+	 *
+	 *  Note this allows 3 flows, it is up to the arch_register_cpu()
+	 *  call to reject any that are not supported on a given architecture.
+	 *  A) CPU becomes present.
+	 *  B) Previously invalid logical CPU ID (Same as becoming present)
+	 *  C) CPU already present and now being enabled (and wasn't registered
+	 *     early on an arch that doesn't defer to here)
 	 */
-	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
+	if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
+	     !get_cpu_device(pr->id)) ||
+	    invalid_logical_cpuid(pr->id) ||
+	    !cpu_present(pr->id)) {
 		ret = acpi_processor_hotadd_init(pr, device);
 
 		if (ret)
-- 
2.39.2

[PATCH v6 07/16] ACPI: scan: switch to flags for acpi_scan_check_and_detach();

[Jonathan Cameron]

Precursor patch adds the ability to pass a uintptr_t of flags into
acpi_scan_check_and detach() so that additional flags can be
added to indicate whether to defer portions of the eject flow.
The new flag follows in the next patch.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v6: Based on internal feedback switch to less invasive change
    to using flags rather than a struct.
v5: New patch resulting from rebase.
    - Internal review suggested we could also do this with flags
      so I'm looking for feedback on which option people find
      more readable.
---
 drivers/acpi/scan.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index d1464324de95..1ec9677e6c2d 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -244,13 +244,16 @@ static int acpi_scan_try_to_offline(struct acpi_device *device)
 	return 0;
 }
 
-static int acpi_scan_check_and_detach(struct acpi_device *adev, void *check)
+#define ACPI_SCAN_CHECK_FLAG_STATUS	BIT(0)
+
+static int acpi_scan_check_and_detach(struct acpi_device *adev, void *p)
 {
 	struct acpi_scan_handler *handler = adev->handler;
+	uintptr_t flags = (uintptr_t)p;
 
-	acpi_dev_for_each_child_reverse(adev, acpi_scan_check_and_detach, check);
+	acpi_dev_for_each_child_reverse(adev, acpi_scan_check_and_detach, p);
 
-	if (check) {
+	if (flags & ACPI_SCAN_CHECK_FLAG_STATUS) {
 		acpi_bus_get_status(adev);
 		/*
 		 * Skip devices that are still there and take the enabled
@@ -288,7 +291,9 @@ static int acpi_scan_check_and_detach(struct acpi_device *adev, void *check)
 
 static void acpi_scan_check_subtree(struct acpi_device *adev)
 {
-	acpi_scan_check_and_detach(adev, (void *)true);
+	uintptr_t flags = ACPI_SCAN_CHECK_FLAG_STATUS;
+
+	acpi_scan_check_and_detach(adev, (void *)flags);
 }
 
 static int acpi_scan_hot_remove(struct acpi_device *device)
@@ -2601,7 +2606,9 @@ EXPORT_SYMBOL(acpi_bus_scan);
  */
 void acpi_bus_trim(struct acpi_device *adev)
 {
-	acpi_scan_check_and_detach(adev, NULL);
+	uintptr_t flags = 0;
+
+	acpi_scan_check_and_detach(adev, (void *)flags);
 }
 EXPORT_SYMBOL_GPL(acpi_bus_trim);
 
-- 
2.39.2

[PATCH v6 08/16] ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

struct acpi_scan_handler has a detach callback that is used to remove
a driver when a bus is changed. When interacting with an eject-request,
the detach callback is called before _EJ0.

This means the ACPI processor driver can't use _STA to determine if a
CPU has been made not-present, or some of the other _STA bits have been
changed. acpi_processor_remove() needs to know the value of _STA after
_EJ0 has been called.

Add a post_eject callback to struct acpi_scan_handler. This is called
after acpi_scan_hot_remove() has successfully called _EJ0. Because
acpi_scan_check_and_detach() also clears the handler pointer,
it needs to be told if the caller will go on to call
acpi_bus_post_eject(), so that acpi_device_clear_enumerated()
and clearing the handler pointer can be deferred.
An extra flag is added to flags field introduced in the previous
patch to achieve this.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

----
v6:
 - Switch to flags.
Russell, you hadn't signed off on this when posting last time.
Do you want to insert a suitable tag now?
v5:
 - Rebase to take into account the changes to scan handling in the
   meantime.
---
 drivers/acpi/acpi_processor.c |  4 ++--
 drivers/acpi/scan.c           | 30 +++++++++++++++++++++++++++---
 include/acpi/acpi_bus.h       |  1 +
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 0cac77961020..0e43f5b4267a 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -481,7 +481,7 @@ static int acpi_processor_add(struct acpi_device *device,
 
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 /* Removal */
-static void acpi_processor_remove(struct acpi_device *device)
+static void acpi_processor_post_eject(struct acpi_device *device)
 {
 	struct acpi_processor *pr;
 
@@ -650,7 +650,7 @@ static struct acpi_scan_handler processor_handler = {
 	.ids = processor_device_ids,
 	.attach = acpi_processor_add,
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
-	.detach = acpi_processor_remove,
+	.post_eject = acpi_processor_post_eject,
 #endif
 	.hotplug = {
 		.enabled = true,
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 1ec9677e6c2d..3ec54624664a 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -245,6 +245,7 @@ static int acpi_scan_try_to_offline(struct acpi_device *device)
 }
 
 #define ACPI_SCAN_CHECK_FLAG_STATUS	BIT(0)
+#define ACPI_SCAN_CHECK_FLAG_EJECT	BIT(1)
 
 static int acpi_scan_check_and_detach(struct acpi_device *adev, void *p)
 {
@@ -273,8 +274,6 @@ static int acpi_scan_check_and_detach(struct acpi_device *adev, void *p)
 	if (handler) {
 		if (handler->detach)
 			handler->detach(adev);
-
-		adev->handler = NULL;
 	} else {
 		device_release_driver(&adev->dev);
 	}
@@ -284,6 +283,28 @@ static int acpi_scan_check_and_detach(struct acpi_device *adev, void *p)
 	 */
 	acpi_device_set_power(adev, ACPI_STATE_D3_COLD);
 	adev->flags.initialized = false;
+
+	/* For eject this is deferred to acpi_bus_post_eject() */
+	if (!(flags & ACPI_SCAN_CHECK_FLAG_EJECT)) {
+		adev->handler = NULL;
+		acpi_device_clear_enumerated(adev);
+	}
+	return 0;
+}
+
+static int acpi_bus_post_eject(struct acpi_device *adev, void *not_used)
+{
+	struct acpi_scan_handler *handler = adev->handler;
+
+	acpi_dev_for_each_child_reverse(adev, acpi_bus_post_eject, NULL);
+
+	if (handler) {
+		if (handler->post_eject)
+			handler->post_eject(adev);
+
+		adev->handler = NULL;
+	}
+
 	acpi_device_clear_enumerated(adev);
 
 	return 0;
@@ -301,6 +322,7 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
 	acpi_handle handle = device->handle;
 	unsigned long long sta;
 	acpi_status status;
+	uintptr_t flags = ACPI_SCAN_CHECK_FLAG_EJECT;
 
 	if (device->handler && device->handler->hotplug.demand_offline) {
 		if (!acpi_scan_is_offline(device, true))
@@ -313,7 +335,7 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
 
 	acpi_handle_debug(handle, "Ejecting\n");
 
-	acpi_bus_trim(device);
+	acpi_scan_check_and_detach(device, (void *)flags);
 
 	acpi_evaluate_lck(handle, 0);
 	/*
@@ -336,6 +358,8 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
 	} else if (sta & ACPI_STA_DEVICE_ENABLED) {
 		acpi_handle_warn(handle,
 			"Eject incomplete - status 0x%llx\n", sta);
+	} else {
+		acpi_bus_post_eject(device, NULL);
 	}
 
 	return 0;
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index e7796f373d0d..51a4b936f19e 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -129,6 +129,7 @@ struct acpi_scan_handler {
 	bool (*match)(const char *idstr, const struct acpi_device_id **matchid);
 	int (*attach)(struct acpi_device *dev, const struct acpi_device_id *id);
 	void (*detach)(struct acpi_device *dev);
+	void (*post_eject)(struct acpi_device *dev);
 	void (*bind)(struct device *phys_dev);
 	void (*unbind)(struct device *phys_dev);
 	struct acpi_hotplug_profile hotplug;
-- 
2.39.2

[PATCH v6 09/16] arm64: acpi: Move get_cpu_for_acpi_id() to a header

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

ACPI identifies CPUs by UID. get_cpu_for_acpi_id() maps the ACPI UID
to the Linux CPU number.

The helper to retrieve this mapping is only available in arm64's NUMA
code.

Move it to live next to get_acpi_id_for_cpu().

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v5: No change
---
 arch/arm64/include/asm/acpi.h | 11 +++++++++++
 arch/arm64/kernel/acpi_numa.c | 11 -----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
index 6792a1f83f2a..bc9a6656fc0c 100644
--- a/arch/arm64/include/asm/acpi.h
+++ b/arch/arm64/include/asm/acpi.h
@@ -119,6 +119,17 @@ static inline u32 get_acpi_id_for_cpu(unsigned int cpu)
 	return	acpi_cpu_get_madt_gicc(cpu)->uid;
 }
 
+static inline int get_cpu_for_acpi_id(u32 uid)
+{
+	int cpu;
+
+	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
+		if (uid == get_acpi_id_for_cpu(cpu))
+			return cpu;
+
+	return -EINVAL;
+}
+
 static inline void arch_fix_phys_package_id(int num, u32 slot) { }
 void __init acpi_init_cpus(void);
 int apei_claim_sea(struct pt_regs *regs);
diff --git a/arch/arm64/kernel/acpi_numa.c b/arch/arm64/kernel/acpi_numa.c
index e51535a5f939..0c036a9a3c33 100644
--- a/arch/arm64/kernel/acpi_numa.c
+++ b/arch/arm64/kernel/acpi_numa.c
@@ -34,17 +34,6 @@ int __init acpi_numa_get_nid(unsigned int cpu)
 	return acpi_early_node_map[cpu];
 }
 
-static inline int get_cpu_for_acpi_id(u32 uid)
-{
-	int cpu;
-
-	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
-		if (uid == get_acpi_id_for_cpu(cpu))
-			return cpu;
-
-	return -EINVAL;
-}
-
 static int __init acpi_parse_gicc_pxm(union acpi_subtable_headers *header,
 				      const unsigned long end)
 {
-- 
2.39.2

[PATCH v6 10/16] irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc()

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

gic_acpi_match_gicc() is only called via gic_acpi_count_gicr_regions().
It should only count the number of enabled redistributors, but it
also tries to sanity check the GICC entry, currently returning an
error if the Enabled bit is set, but the gicr_base_address is zero.

Adding support for the online-capable bit to the sanity check will
complicate it, for no benefit. The existing check implicitly depends on
gic_acpi_count_gicr_regions() previous failing to find any GICR regions
(as it is valid to have gicr_base_address of zero if the redistributors
are described via a GICR entry).

Instead of complicating the check, remove it. Failures that happen at
this point cause the irqchip not to register, meaning no irqs can be
requested. The kernel grinds to a panic() pretty quickly.

Without the check, MADT tables that exhibit this problem are still
caught by gic_populate_rdist(), which helpfully also prints what went
wrong:
| CPU4: mpidr 100 has no re-distributor!

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v5: No change
---
 drivers/irqchip/irq-gic-v3.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 6fb276504bcc..10af15f93d4d 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -2415,19 +2415,10 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,
 	 * If GICC is enabled and has valid gicr base address, then it means
 	 * GICR base is presented via GICC
 	 */
-	if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address) {
+	if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address)
 		acpi_data.enabled_rdists++;
-		return 0;
-	}
 
-	/*
-	 * It's perfectly valid firmware can pass disabled GICC entry, driver
-	 * should not treat as errors, skip the entry instead of probe fail.
-	 */
-	if (!acpi_gicc_is_usable(gicc))
-		return 0;
-
-	return -ENODEV;
+	return 0;
 }
 
 static int __init gic_acpi_count_gicr_regions(void)
-- 
2.39.2

[PATCH v6 11/16] irqchip/gic-v3: Add support for ACPI's disabled but 'online capable' CPUs

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

To support virtual CPU hotplug, ACPI has added an 'online capable' bit
to the MADT GICC entries. This indicates a disabled CPU entry may not
be possible to online via PSCI until firmware has set enabled bit in
_STA.

This means that a "usable" GIC is one that is marked as either enabled,
or online capable. Therefore, change acpi_gicc_is_usable() to check both
bits. However, we need to change the test in gic_acpi_match_gicc() back
to testing just the enabled bit so the count of enabled distributors is
correct.

What about the redistributor in the GICC entry? ACPI doesn't want to say.
Assume the worst: When a redistributor is described in the GICC entry,
but the entry is marked as disabled at boot, assume the redistributor
is inaccessible.

The GICv3 driver doesn't support late online of redistributors, so this
means the corresponding CPU can't be brought online either. Clear the
possible and present bits.

Systems that want CPU hotplug in a VM can ensure their redistributors
are always-on, and describe them that way with a GICR entry in the MADT.

When mapping redistributors found via GICC entries, handle the case
where the arch code believes the CPU is present and possible, but it
does not have an accessible redistributor. Print a warning and clear
the present and possible bits.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v5: No Change.
---
 drivers/irqchip/irq-gic-v3.c | 21 +++++++++++++++++++--
 include/linux/acpi.h         |  3 ++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 10af15f93d4d..66132251c1bb 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -2363,11 +2363,25 @@ gic_acpi_parse_madt_gicc(union acpi_subtable_headers *header,
 				(struct acpi_madt_generic_interrupt *)header;
 	u32 reg = readl_relaxed(acpi_data.dist_base + GICD_PIDR2) & GIC_PIDR2_ARCH_MASK;
 	u32 size = reg == GIC_PIDR2_ARCH_GICv4 ? SZ_64K * 4 : SZ_64K * 2;
+	int cpu = get_cpu_for_acpi_id(gicc->uid);
 	void __iomem *redist_base;
 
 	if (!acpi_gicc_is_usable(gicc))
 		return 0;
 
+	/*
+	 * Capable but disabled CPUs can be brought online later. What about
+	 * the redistributor? ACPI doesn't want to say!
+	 * Virtual hotplug systems can use the MADT's "always-on" GICR entries.
+	 * Otherwise, prevent such CPUs from being brought online.
+	 */
+	if (!(gicc->flags & ACPI_MADT_ENABLED)) {
+		pr_warn_once("CPU %u's redistributor is inaccessible: this CPU can't be brought online\n", cpu);
+		set_cpu_present(cpu, false);
+		set_cpu_possible(cpu, false);
+		return 0;
+	}
+
 	redist_base = ioremap(gicc->gicr_base_address, size);
 	if (!redist_base)
 		return -ENOMEM;
@@ -2413,9 +2427,12 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,
 
 	/*
 	 * If GICC is enabled and has valid gicr base address, then it means
-	 * GICR base is presented via GICC
+	 * GICR base is presented via GICC. The redistributor is only known to
+	 * be accessible if the GICC is marked as enabled. If this bit is not
+	 * set, we'd need to add the redistributor at runtime, which isn't
+	 * supported.
 	 */
-	if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address)
+	if (gicc->flags & ACPI_MADT_ENABLED && gicc->gicr_base_address)
 		acpi_data.enabled_rdists++;
 
 	return 0;
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 9844a3f9c4e5..fcfb7bb6789e 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -239,7 +239,8 @@ void acpi_table_print_madt_entry (struct acpi_subtable_header *madt);
 
 static inline bool acpi_gicc_is_usable(struct acpi_madt_generic_interrupt *gicc)
 {
-	return gicc->flags & ACPI_MADT_ENABLED;
+	return gicc->flags & (ACPI_MADT_ENABLED |
+			      ACPI_MADT_GICC_ONLINE_CAPABLE);
 }
 
 /* the following numa functions are architecture-dependent */
-- 
2.39.2

[PATCH v6 12/16] arm64: psci: Ignore DENIED CPUs

[Jonathan Cameron]

From: Jean-Philippe Brucker <jean-philippe@linaro.org>

When a CPU is marked as disabled, but online capable in the MADT, PSCI
applies some firmware policy to control when it can be brought online.
PSCI returns DENIED to a CPU_ON request if this is not currently
permitted. The OS can learn the current policy from the _STA enabled bit.

Handle the PSCI DENIED return code gracefully instead of printing an
error.

See https://developer.arm.com/documentation/den0022/f/?lang=en page 58.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
[ morse: Rewrote commit message ]
Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v5: No change
---
 arch/arm64/kernel/psci.c | 2 +-
 arch/arm64/kernel/smp.c  | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index 29a8e444db83..fabd732d0a2d 100644
--- a/arch/arm64/kernel/psci.c
+++ b/arch/arm64/kernel/psci.c
@@ -40,7 +40,7 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
 {
 	phys_addr_t pa_secondary_entry = __pa_symbol(secondary_entry);
 	int err = psci_ops.cpu_on(cpu_logical_map(cpu), pa_secondary_entry);
-	if (err)
+	if (err && err != -EPERM)
 		pr_err("failed to boot CPU%d (%d)\n", cpu, err);
 
 	return err;
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 4ced34f62dab..dc0e0b3ec2d4 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -132,7 +132,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	/* Now bring the CPU into our world */
 	ret = boot_secondary(cpu, idle);
 	if (ret) {
-		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
+		if (ret != -EPERM)
+			pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
 		return ret;
 	}
 
-- 
2.39.2

[PATCH v6 13/16] arm64: arch_register_cpu() variant to check if an ACPI handle is now available.

[Jonathan Cameron]

The ARM64 architecture does not support physical CPU HP today.
To avoid any possibility of a bug against such an architecture if defined
in future, check for the physical CPU HP case (not present) and
return an error on any such attempt.

On ARM64 virtual CPU Hotplug relies on the status value that can be
queried via the AML method _STA for the CPU object.

There are two conditions in which the CPU can be registered.
1) ACPI disabled.
2) ACPI enabled and the acpi_handle is available.
   _STA evaluates to the CPU is both enabled and present.
   (Note that in absence of the _STA method they are always in this
    state).

If neither of these conditions is met the CPU is not 'yet' ready
to be used and -EPROBE_DEFER is returned.

Success occurs in the early attempt to register the CPUs if we
are booting with DT (no concept yet of vCPU HP) if not it succeeds
for already enabled CPUs when the ACPI Processor driver attaches to
them.  Finally it may succeed via the CPU Hotplug code indicating that
the CPU is now enabled.

For ACPI if CONFIG_ACPI_PROCESSOR the only path to get to
arch_register_cpu() with that handle set is via
acpi_processor_hot_add_init() which is only called from an ACPI bus
scan in which _STA has already been queried there is no need to
repeat it here. Add a comment to remind us of this in the future.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
v6: Add protection again Physical CPU HP to the arch specific code
    and don't actually check _STA

Tested on arm64 with ACPI + DT build and DT only builds, booting
with ACPI and DT as appropriate.
---
 arch/arm64/kernel/smp.c | 53 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index dc0e0b3ec2d4..ccb6ad347df9 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -504,6 +504,59 @@ static int __init smp_cpu_setup(int cpu)
 static bool bootcpu_valid __initdata;
 static unsigned int cpu_count = 1;
 
+int arch_register_cpu(int cpu)
+{
+	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
+	struct cpu *c = &per_cpu(cpu_devices, cpu);
+
+	if (!acpi_disabled && !acpi_handle &&
+	    IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
+		return -EPROBE_DEFER;
+
+#ifdef CONFIG_ACPI_HOTPLUG_CPU
+	/* For now block anything that looks like physical CPU Hotplug */
+	if (invalid_logical_cpuid(cpu) || !cpu_present(cpu)) {
+		pr_err_once("Changing CPU present bit is not supported\n");
+		return -ENODEV;
+	}
+#endif
+
+	/*
+	 * Availability of the acpi handle is sufficient to establish
+	 * that _STA has aleady been checked. No need to recheck here.
+	 */
+	c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
+
+	return register_cpu(c, cpu);
+}
+
+#ifdef CONFIG_ACPI_HOTPLUG_CPU
+void arch_unregister_cpu(int cpu)
+{
+	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
+	struct cpu *c = &per_cpu(cpu_devices, cpu);
+	acpi_status status;
+	unsigned long long sta;
+
+	if (!acpi_handle) {
+		pr_err_once("Removing a CPU without associated ACPI handle\n");
+		return;
+	}
+
+	status = acpi_evaluate_integer(acpi_handle, "_STA", NULL, &sta);
+	if (ACPI_FAILURE(status))
+		return;
+
+	/* For now do not allow anything that looks like physical CPU HP */
+	if (cpu_present(cpu) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
+		pr_err_once("Changing CPU present bit is not supported\n");
+		return;
+	}
+
+	unregister_cpu(c);
+}
+#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+
 #ifdef CONFIG_ACPI
 static struct acpi_madt_generic_interrupt cpu_madt_gicc[NR_CPUS];
 
-- 
2.39.2

[PATCH v6 14/16] arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is enabled.

[Jonathan Cameron]

In order to move arch_register_cpu() to be called via the same path
for initially present CPUs described by ACPI and hotplugged CPUs
ACPI_HOTPLUG_CPU needs to be enabled.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 arch/arm64/Kconfig       |  1 +
 arch/arm64/kernel/acpi.c | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b11c98b3e84..fed7d0d54179 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -5,6 +5,7 @@ config ARM64
 	select ACPI_CCA_REQUIRED if ACPI
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_GTDT if ACPI
+	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR
 	select ACPI_IORT if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_MCFG if (ACPI && PCI)
diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index dba8fcec7f33..a74e80d58df3 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -29,6 +29,7 @@
 #include <linux/pgtable.h>
 
 #include <acpi/ghes.h>
+#include <acpi/processor.h>
 #include <asm/cputype.h>
 #include <asm/cpu_ops.h>
 #include <asm/daifflags.h>
@@ -413,6 +414,21 @@ void arch_reserve_mem_area(acpi_physical_address addr, size_t size)
 	memblock_mark_nomap(addr, size);
 }
 
+#ifdef CONFIG_ACPI_HOTPLUG_CPU
+int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 apci_id,
+		 int *pcpu)
+{
+	return 0;
+}
+EXPORT_SYMBOL(acpi_map_cpu); /* check why */
+
+int acpi_unmap_cpu(int cpu)
+{
+	return 0;
+}
+EXPORT_SYMBOL(acpi_unmap_cpu);
+#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+
 #ifdef CONFIG_ACPI_FFH
 /*
  * Implements ARM64 specific callbacks to support ACPI FFH Operation Region as
-- 
2.39.2

[PATCH v6 15/16] arm64: document virtual CPU hotplug's expectations

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

Add a description of physical and virtual CPU hotplug, explain the
differences and elaborate on what is required in ACPI for a working
virtual hotplug system.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v5: No change.
---
 Documentation/arch/arm64/cpu-hotplug.rst | 79 ++++++++++++++++++++++++
 Documentation/arch/arm64/index.rst       |  1 +
 2 files changed, 80 insertions(+)

diff --git a/Documentation/arch/arm64/cpu-hotplug.rst b/Documentation/arch/arm64/cpu-hotplug.rst
new file mode 100644
index 000000000000..76ba8d932c72
--- /dev/null
+++ b/Documentation/arch/arm64/cpu-hotplug.rst
@@ -0,0 +1,79 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. _cpuhp_index:
+
+====================
+CPU Hotplug and ACPI
+====================
+
+CPU hotplug in the arm64 world is commonly used to describe the kernel taking
+CPUs online/offline using PSCI. This document is about ACPI firmware allowing
+CPUs that were not available during boot to be added to the system later.
+
+``possible`` and ``present`` refer to the state of the CPU as seen by linux.
+
+
+CPU Hotplug on physical systems - CPUs not present at boot
+----------------------------------------------------------
+
+Physical systems need to mark a CPU that is ``possible`` but not ``present`` as
+being ``present``. An example would be a dual socket machine, where the package
+in one of the sockets can be replaced while the system is running.
+
+This is not supported.
+
+In the arm64 world CPUs are not a single device but a slice of the system.
+There are no systems that support the physical addition (or removal) of CPUs
+while the system is running, and ACPI is not able to sufficiently describe
+them.
+
+e.g. New CPUs come with new caches, but the platform's cache toplogy is
+described in a static table, the PPTT. How caches are shared between CPUs is
+not discoverable, and must be described by firmware.
+
+e.g. The GIC redistributor for each CPU must be accessed by the driver during
+boot to discover the system wide supported features. ACPI's MADT GICC
+structures can describe a redistributor associated with a disabled CPU, but
+can't describe whether the redistributor is accessible, only that it is not
+'always on'.
+
+arm64's ACPI tables assume that everything described is ``present``.
+
+
+CPU Hotplug on virtual systems - CPUs not enabled at boot
+---------------------------------------------------------
+
+Virtual systems have the advantage that all the properties the system will
+ever have can be described at boot. There are no power-domain considerations
+as such devices are emulated.
+
+CPU Hotplug on virtual systems is supported. It is distinct from physical
+CPU Hotplug as all resources are described as ``present``, but CPUs may be
+marked as disabled by firmware. Only the CPU's online/offline behaviour is
+influenced by firmware. An example is where a virtual machine boots with a
+single CPU, and additional CPUs are added once a cloud orchestrator deploys
+the workload.
+
+For a virtual machine, the VMM (e.g. Qemu) plays the part of firmware.
+
+Virtual hotplug is implemented as a firmware policy affecting which CPUs can be
+brought online. Firmware can enforce its policy via PSCI's return codes. e.g.
+``DENIED``.
+
+The ACPI tables must describe all the resources of the virtual machine. CPUs
+that firmware wishes to disable either from boot (or later) should not be
+``enabled`` in the MADT GICC structures, but should have the ``online capable``
+bit set, to indicate they can be enabled later. The boot CPU must be marked as
+``enabled``.  The 'always on' GICR structure must be used to describe the
+redistributors.
+
+CPUs described as ``online capable`` but not ``enabled`` can be set to enabled
+by the DSDT's Processor object's _STA method. On virtual systems the _STA method
+must always report the CPU as ``present``. Changes to the firmware policy can
+be notified to the OS via device-check or eject-request.
+
+CPUs described as ``enabled`` in the static table, should not have their _STA
+modified dynamically by firmware. Soft-restart features such as kexec will
+re-read the static properties of the system from these static tables, and
+may malfunction if these no longer describe the running system. Linux will
+re-discover the dynamic properties of the system from the _STA method later
+during boot.
diff --git a/Documentation/arch/arm64/index.rst b/Documentation/arch/arm64/index.rst
index d08e924204bf..78544de0a8a9 100644
--- a/Documentation/arch/arm64/index.rst
+++ b/Documentation/arch/arm64/index.rst
@@ -13,6 +13,7 @@ ARM64 Architecture
     asymmetric-32bit
     booting
     cpu-feature-registers
+    cpu-hotplug
     elf_hwcaps
     hugetlbpage
     kdump
-- 
2.39.2

[PATCH v6 16/16] cpumask: Add enabled cpumask for present CPUs that can be brought online

[Jonathan Cameron]

From: James Morse <james.morse@arm.com>

The 'offline' file in sysfs shows all offline CPUs, including those
that aren't present. User-space is expected to remove not-present CPUs
from this list to learn which CPUs could be brought online.

CPUs can be present but not-enabled. These CPUs can't be brought online
until the firmware policy changes, which comes with an ACPI notification
that will register the CPUs.

With only the offline and present files, user-space is unable to
determine which CPUs it can try to bring online. Add a new CPU mask
that shows this based on all the registered CPUs.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v5: No change
---
 .../ABI/testing/sysfs-devices-system-cpu      |  6 +++++
 drivers/base/cpu.c                            | 10 ++++++++
 include/linux/cpumask.h                       | 25 +++++++++++++++++++
 kernel/cpu.c                                  |  3 +++
 4 files changed, 44 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 710d47be11e0..808efb5b860a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -694,3 +694,9 @@ Description:
 		(RO) indicates whether or not the kernel directly supports
 		modifying the crash elfcorehdr for CPU hot un/plug and/or
 		on/offline changes.
+
+What:		/sys/devices/system/cpu/enabled
+Date:		Nov 2022
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:
+		(RO) the list of CPUs that can be brought online.
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index b9d0d14e5960..4713b86d20f2 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)
 {
 	int logical_cpu = cpu->dev.id;
 
+	set_cpu_enabled(logical_cpu, false);
 	unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
 
 	device_unregister(&cpu->dev);
@@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
 }
 static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
 
+static ssize_t print_cpus_enabled(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_enabled_mask));
+}
+static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);
+
 static ssize_t print_cpus_isolated(struct device *dev,
 				  struct device_attribute *attr, char *buf)
 {
@@ -413,6 +421,7 @@ int register_cpu(struct cpu *cpu, int num)
 	register_cpu_under_node(num, cpu_to_node(num));
 	dev_pm_qos_expose_latency_limit(&cpu->dev,
 					PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+	set_cpu_enabled(num, true);
 
 	return 0;
 }
@@ -494,6 +503,7 @@ static struct attribute *cpu_root_attrs[] = {
 	&cpu_attrs[2].attr.attr,
 	&dev_attr_kernel_max.attr,
 	&dev_attr_offline.attr,
+	&dev_attr_enabled.attr,
 	&dev_attr_isolated.attr,
 #ifdef CONFIG_NO_HZ_FULL
 	&dev_attr_nohz_full.attr,
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 1c29947db848..4b202b94c97a 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -93,6 +93,7 @@ static inline void set_nr_cpu_ids(unsigned int nr)
  *
  *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
  *     cpu_present_mask - has bit 'cpu' set iff cpu is populated
+ *     cpu_enabled_mask  - has bit 'cpu' set iff cpu can be brought online
  *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
  *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
  *
@@ -125,11 +126,13 @@ static inline void set_nr_cpu_ids(unsigned int nr)
 
 extern struct cpumask __cpu_possible_mask;
 extern struct cpumask __cpu_online_mask;
+extern struct cpumask __cpu_enabled_mask;
 extern struct cpumask __cpu_present_mask;
 extern struct cpumask __cpu_active_mask;
 extern struct cpumask __cpu_dying_mask;
 #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
 #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
+#define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
 #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
 #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
 #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
@@ -1009,6 +1012,7 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
 #else
 #define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
 #define for_each_online_cpu(cpu)   for_each_cpu((cpu), cpu_online_mask)
+#define for_each_enabled_cpu(cpu)   for_each_cpu((cpu), cpu_enabled_mask)
 #define for_each_present_cpu(cpu)  for_each_cpu((cpu), cpu_present_mask)
 #endif
 
@@ -1031,6 +1035,15 @@ set_cpu_possible(unsigned int cpu, bool possible)
 		cpumask_clear_cpu(cpu, &__cpu_possible_mask);
 }
 
+static inline void
+set_cpu_enabled(unsigned int cpu, bool can_be_onlined)
+{
+	if (can_be_onlined)
+		cpumask_set_cpu(cpu, &__cpu_enabled_mask);
+	else
+		cpumask_clear_cpu(cpu, &__cpu_enabled_mask);
+}
+
 static inline void
 set_cpu_present(unsigned int cpu, bool present)
 {
@@ -1112,6 +1125,7 @@ static __always_inline unsigned int num_online_cpus(void)
 	return raw_atomic_read(&__num_online_cpus);
 }
 #define num_possible_cpus()	cpumask_weight(cpu_possible_mask)
+#define num_enabled_cpus()	cpumask_weight(cpu_enabled_mask)
 #define num_present_cpus()	cpumask_weight(cpu_present_mask)
 #define num_active_cpus()	cpumask_weight(cpu_active_mask)
 
@@ -1120,6 +1134,11 @@ static inline bool cpu_online(unsigned int cpu)
 	return cpumask_test_cpu(cpu, cpu_online_mask);
 }
 
+static inline bool cpu_enabled(unsigned int cpu)
+{
+	return cpumask_test_cpu(cpu, cpu_enabled_mask);
+}
+
 static inline bool cpu_possible(unsigned int cpu)
 {
 	return cpumask_test_cpu(cpu, cpu_possible_mask);
@@ -1144,6 +1163,7 @@ static inline bool cpu_dying(unsigned int cpu)
 
 #define num_online_cpus()	1U
 #define num_possible_cpus()	1U
+#define num_enabled_cpus()	1U
 #define num_present_cpus()	1U
 #define num_active_cpus()	1U
 
@@ -1157,6 +1177,11 @@ static inline bool cpu_possible(unsigned int cpu)
 	return cpu == 0;
 }
 
+static inline bool cpu_enabled(unsigned int cpu)
+{
+	return cpu == 0;
+}
+
 static inline bool cpu_present(unsigned int cpu)
 {
 	return cpu == 0;
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 07ad53b7f119..6d228f1c4e39 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3117,6 +3117,9 @@ EXPORT_SYMBOL(__cpu_possible_mask);
 struct cpumask __cpu_online_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_online_mask);
 
+struct cpumask __cpu_enabled_mask __read_mostly;
+EXPORT_SYMBOL(__cpu_enabled_mask);
+
 struct cpumask __cpu_present_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_present_mask);
 
-- 
2.39.2

Re: [PATCH v6 02/16] cpu: Do not warn on arch_register_cpu() returning -EPROBE_DEFER

[Russell King (Oracle)]

On Wed, Apr 17, 2024 at 02:18:55PM +0100, Jonathan Cameron wrote:
> For arm64 the CPU registration cannot complete until the ACPI
> interpreter us up and running so in those cases the arch specific
> arch_register_cpu() will return -EPROBE_DEFER at this stage and the
> registration will be attempted later.
> 
> Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
> Acked-by: Rafael J. Wysocki <rafael@kernel.org>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> 
> ---
> v6: tags
> ---
>  drivers/base/cpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 56fba44ba391..b9d0d14e5960 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -558,7 +558,7 @@ static void __init cpu_dev_register_generic(void)
>  
>  	for_each_present_cpu(i) {
>  		ret = arch_register_cpu(i);
> -		if (ret)
> +		if (ret != -EPROBE_DEFER)
>  			pr_warn("register_cpu %d failed (%d)\n", i, ret);

This looks very broken to me.

		if (ret && ret != -EPROBE_DEFER)

surely, because we don't want to print a warning if arch_register_cpu()
was successful?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: [PATCH v6 02/16] cpu: Do not warn on arch_register_cpu() returning -EPROBE_DEFER

[Jonathan Cameron]

On Wed, 17 Apr 2024 15:01:33 +0100
"Russell King (Oracle)" <linux@armlinux.org.uk> wrote:

> On Wed, Apr 17, 2024 at 02:18:55PM +0100, Jonathan Cameron wrote:
> > For arm64 the CPU registration cannot complete until the ACPI
> > interpreter us up and running so in those cases the arch specific
> > arch_register_cpu() will return -EPROBE_DEFER at this stage and the
> > registration will be attempted later.
> > 
> > Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
> > Acked-by: Rafael J. Wysocki <rafael@kernel.org>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > 
> > ---
> > v6: tags
> > ---
> >  drivers/base/cpu.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> > index 56fba44ba391..b9d0d14e5960 100644
> > --- a/drivers/base/cpu.c
> > +++ b/drivers/base/cpu.c
> > @@ -558,7 +558,7 @@ static void __init cpu_dev_register_generic(void)
> >  
> >  	for_each_present_cpu(i) {
> >  		ret = arch_register_cpu(i);
> > -		if (ret)
> > +		if (ret != -EPROBE_DEFER)
> >  			pr_warn("register_cpu %d failed (%d)\n", i, ret);  
> 
> This looks very broken to me.
> 
> 		if (ret && ret != -EPROBE_DEFER)
> 
> surely, because we don't want to print a warning if arch_register_cpu()
> was successful?

Gah.  Excellent point.

thanks,

Jonathan

> 

RE: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Salil Mehta]

>  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  Sent: Wednesday, April 17, 2024 2:19 PM
>  
>  From: James Morse <james.morse@arm.com>
>  
>  The arm64 specific arch_register_cpu() call may defer CPU registration until
>  the ACPI interpreter is available and the _STA method can be evaluated.
>  
>  If this occurs, then a second attempt is made in acpi_processor_get_info().
>  Note that the arm64 specific call has not yet been added so for now this will
>  be called for the original hotplug case.
>  
>  For architectures that do not defer until the ACPI Processor driver loads
>  (e.g. x86), for initially present CPUs there will already be a CPU device. If
>  present do not try to register again.
>  
>  Systems can still be booted with 'acpi=off', or not include an ACPI
>  description at all as in these cases arch_register_cpu() will not have
>  deferred registration when first called.
>  
>  This moves the CPU register logic back to a subsys_initcall(), while the
>  memory nodes will have been registered earlier.
>  Note this is where the call was prior to the cleanup series so there should be
>  no side effects of moving it back again for this specific case.
>  
>  [PATCH 00/21] Initial cleanups for vCPU HP.
>  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
>  
>  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
>  
>  Signed-off-by: James Morse <james.morse@arm.com>
>  Reviewed-by: Gavin Shan <gshan@redhat.com>
>  Tested-by: Miguel Luis <miguel.luis@oracle.com>
>  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
>  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
>  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
>  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
>  ---
>  v6: Squash the two paths for conventional CPU Hotplug and arm64
>      vCPU HP.
>  v5: Update commit message to make it clear this is moving the
>      init back to where it was until very recently.
>  
>      No longer change the condition in the earlier registration point
>      as that will be handled by the arm64 registration routine
>      deferring until called again here.
>  ---
>   drivers/acpi/acpi_processor.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
>  
>  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
>  index 7ecb13775d7f..0cac77961020 100644
>  --- a/drivers/acpi/acpi_processor.c
>  +++ b/drivers/acpi/acpi_processor.c
>  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
>  acpi_device *device)
>   	 *
>   	 *  NOTE: Even if the processor has a cpuid, it may not be present
>   	 *  because cpuid <-> apicid mapping is persistent now.
>  +	 *
>  +	 *  Note this allows 3 flows, it is up to the arch_register_cpu()
>  +	 *  call to reject any that are not supported on a given architecture.
>  +	 *  A) CPU becomes present.
>  +	 *  B) Previously invalid logical CPU ID (Same as becoming present)
>  +	 *  C) CPU already present and now being enabled (and wasn't
>  registered
>  +	 *     early on an arch that doesn't defer to here)
>   	 */
>  -	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
>  +	if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
>  +	     !get_cpu_device(pr->id)) ||
>  +	    invalid_logical_cpuid(pr->id) ||
>  +	    !cpu_present(pr->id)) {


Logic is clear but it is ugly. We should turn them into macro or inline.


Thanks
Salil.

RE: [PATCH v6 04/16] ACPI: processor: Move checks and availability of acpi_processor earlier

[Salil Mehta]

>  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  Sent: Wednesday, April 17, 2024 2:19 PM
>  
>  Make the per_cpu(processors, cpu) entries available earlier so that they are
>  available in arch_register_cpu() as ARM64 will need access to the
>  acpi_handle to distinguish between acpi_processor_add() and earlier
>  registration attempts (which will fail as _STA cannot be checked).
>  
>  Reorder the remove flow to clear this per_cpu() after
>  arch_unregister_cpu() has completed, allowing it to be used in there as
>  well.
>  
>  Note that on x86 for the CPU hotplug case, the pr->id prior to
>  acpi_map_cpu() may be invalid. Thus the per_cpu() structures must be
>  initialized after that call or after checking the ID is valid (not hotplug path).
>  
>  Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  ---
>  v6: As per discussion in v5 thread, don't use the cpu->dev and
>      make this data available earlier by moving the assignment checks
>      int acpi_processor_get_info().
>  ---
>   drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++--------------
>   1 file changed, 47 insertions(+), 32 deletions(-)
>  
>  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
>  index ba0a6f0ac841..2c164451ab53 100644
>  --- a/drivers/acpi/acpi_processor.c
>  +++ b/drivers/acpi/acpi_processor.c
>  @@ -184,7 +184,35 @@ static void __init acpi_pcc_cpufreq_init(void) {}
>  
>   /* Initialization */
>   #ifdef CONFIG_ACPI_HOTPLUG_CPU
>  -static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>  +static DEFINE_PER_CPU(void *, processor_device_array);
>  +
>  +static void acpi_processor_set_per_cpu(struct acpi_processor *pr,
>  +				       struct acpi_device *device)
>  +{
>  +	BUG_ON(pr->id >= nr_cpu_ids);
>  +	/*
>  +	 * Buggy BIOS check.
>  +	 * ACPI id of processors can be reported wrongly by the BIOS.
>  +	 * Don't trust it blindly
>  +	 */
>  +	if (per_cpu(processor_device_array, pr->id) != NULL &&
>  +	    per_cpu(processor_device_array, pr->id) != device) {
>  +		dev_warn(&device->dev,
>  +			 "BIOS reported wrong ACPI id %d for the  processor\n",
>  +			 pr->id);
>  +		/* Give up, but do not abort the namespace scan. */
>  +		return;
>  +	}
>  +	/*
>  +	 * processor_device_array is not cleared on errors to allow buggy  BIOS
>  +	 * checks.
>  +	 */
>  +	per_cpu(processor_device_array, pr->id) = device;
>  +	per_cpu(processors, pr->id) = pr;
>  +}
>  +
>  +static int acpi_processor_hotadd_init(struct acpi_processor *pr,
>  +				      struct acpi_device *device)
>   {
>   	int ret;
>  
>  @@ -198,6 +226,8 @@ static int acpi_processor_hotadd_init(struct
>  acpi_processor *pr)
>   	if (ret)
>   		goto out;
>  
>  +	acpi_processor_set_per_cpu(pr, device);
>  +
>   	ret = arch_register_cpu(pr->id);
>   	if (ret) {
>   		acpi_unmap_cpu(pr->id);
>  @@ -217,7 +247,8 @@ static int acpi_processor_hotadd_init(struct
>  acpi_processor *pr)
>   	return ret;
>   }
>   #else
>  -static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
>  +static inline int acpi_processor_hotadd_init(struct acpi_processor *pr,
>  +					     struct acpi_device *device)
>   {
>   	return -ENODEV;
>   }
>  @@ -232,6 +263,7 @@ static int acpi_processor_get_info(struct acpi_device
>  *device)
>   	acpi_status status = AE_OK;
>   	static int cpu0_initialized;
>   	unsigned long long value;
>  +	int ret;
>  
>   	acpi_processor_errata();
>  
>  @@ -316,10 +348,12 @@ static int acpi_processor_get_info(struct
>  acpi_device *device)
>   	 *  because cpuid <-> apicid mapping is persistent now.
>   	 */
>   	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
>  -		int ret = acpi_processor_hotadd_init(pr);
>  +		ret = acpi_processor_hotadd_init(pr, device);
>  
>   		if (ret)
>  -			return ret;
>  +			goto err;
>  +	} else {
>  +		acpi_processor_set_per_cpu(pr, device);
>   	}
>  
>   	/*
>  @@ -357,6 +391,10 @@ static int acpi_processor_get_info(struct
>  acpi_device *device)
>   		arch_fix_phys_package_id(pr->id, value);
>  
>   	return 0;
>  +
>  +err:
>  +	per_cpu(processors, pr->id) = NULL;
>  +	return ret;
>   }
>  
>   /*
>  @@ -365,8 +403,6 @@ static int acpi_processor_get_info(struct acpi_device
>  *device)
>    * (cpu_data(cpu)) values, like CPU feature flags, family, model, etc.
>    * Such things have to be put in and set up by the processor driver's
>  .probe().
>    */
>  -static DEFINE_PER_CPU(void *, processor_device_array);
>  -
>   static int acpi_processor_add(struct acpi_device *device,
>   					const struct acpi_device_id *id)
>   {
>  @@ -395,28 +431,6 @@ static int acpi_processor_add(struct acpi_device
>  *device,
>   	if (result) /* Processor is not physically present or unavailable */
>   		return 0;
>  
>  -	BUG_ON(pr->id >= nr_cpu_ids);
>  -
>  -	/*
>  -	 * Buggy BIOS check.
>  -	 * ACPI id of processors can be reported wrongly by the BIOS.
>  -	 * Don't trust it blindly
>  -	 */
>  -	if (per_cpu(processor_device_array, pr->id) != NULL &&
>  -	    per_cpu(processor_device_array, pr->id) != device) {
>  -		dev_warn(&device->dev,
>  -			"BIOS reported wrong ACPI id %d for the  processor\n",
>  -			pr->id);
>  -		/* Give up, but do not abort the namespace scan. */
>  -		goto err;
>  -	}
>  -	/*
>  -	 * processor_device_array is not cleared on errors to allow buggy  BIOS
>  -	 * checks.
>  -	 */
>  -	per_cpu(processor_device_array, pr->id) = device;
>  -	per_cpu(processors, pr->id) = pr;
>  -
>   	dev = get_cpu_device(pr->id);
>   	if (!dev) {
>   		result = -ENODEV;
>  @@ -469,15 +483,16 @@ static void acpi_processor_remove(struct
>  acpi_device *device)
>   	device_release_driver(pr->dev);
>   	acpi_unbind_one(pr->dev);
>  
>  -	/* Clean up. */
>  -	per_cpu(processor_device_array, pr->id) = NULL;
>  -	per_cpu(processors, pr->id) = NULL;
>  -
>   	cpu_maps_update_begin();
>   	cpus_write_lock();
>  
>   	/* Remove the CPU. */
>   	arch_unregister_cpu(pr->id);
>  +
>  +	/* Clean up. */
>  +	per_cpu(processor_device_array, pr->id) = NULL;
>  +	per_cpu(processors, pr->id) = NULL;
>  +


Shouldn't above change come after acpi_unmap_cpu() i.e. after next line?


>   	acpi_unmap_cpu(pr->id);
>  
>   	cpus_write_unlock();
>  --
>  2.39.2

Re: [PATCH v6 04/16] ACPI: processor: Move checks and availability of acpi_processor earlier

[Jonathan Cameron]

> >   		result = -ENODEV;
> >  @@ -469,15 +483,16 @@ static void acpi_processor_remove(struct
> >  acpi_device *device)
> >   	device_release_driver(pr->dev);
> >   	acpi_unbind_one(pr->dev);
> >  
> >  -	/* Clean up. */
> >  -	per_cpu(processor_device_array, pr->id) = NULL;
> >  -	per_cpu(processors, pr->id) = NULL;
> >  -
> >   	cpu_maps_update_begin();
> >   	cpus_write_lock();
> >  
> >   	/* Remove the CPU. */
> >   	arch_unregister_cpu(pr->id);
> >  +
> >  +	/* Clean up. */
> >  +	per_cpu(processor_device_array, pr->id) = NULL;
> >  +	per_cpu(processors, pr->id) = NULL;
> >  +  
> 
> 
> Shouldn't above change come after acpi_unmap_cpu() i.e. after next line?
> 
> 
> >   	acpi_unmap_cpu(pr->id);
Agreed - that is more logically correct.  I'll move it for v7.

Thanks,

Jonathan

Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Jonathan Cameron]

On Wed, 17 Apr 2024 16:03:51 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> >  Sent: Wednesday, April 17, 2024 2:19 PM
> >  
> >  From: James Morse <james.morse@arm.com>
> >  
> >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> >  the ACPI interpreter is available and the _STA method can be evaluated.
> >  
> >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> >  Note that the arm64 specific call has not yet been added so for now this will
> >  be called for the original hotplug case.
> >  
> >  For architectures that do not defer until the ACPI Processor driver loads
> >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> >  present do not try to register again.
> >  
> >  Systems can still be booted with 'acpi=off', or not include an ACPI
> >  description at all as in these cases arch_register_cpu() will not have
> >  deferred registration when first called.
> >  
> >  This moves the CPU register logic back to a subsys_initcall(), while the
> >  memory nodes will have been registered earlier.
> >  Note this is where the call was prior to the cleanup series so there should be
> >  no side effects of moving it back again for this specific case.
> >  
> >  [PATCH 00/21] Initial cleanups for vCPU HP.
> >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> >  
> >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> >  
> >  Signed-off-by: James Morse <james.morse@arm.com>
> >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> >  ---
> >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> >      vCPU HP.
> >  v5: Update commit message to make it clear this is moving the
> >      init back to where it was until very recently.
> >  
> >      No longer change the condition in the earlier registration point
> >      as that will be handled by the arm64 registration routine
> >      deferring until called again here.
> >  ---
> >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> >   1 file changed, 11 insertions(+), 1 deletion(-)
> >  
> >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> >  index 7ecb13775d7f..0cac77961020 100644
> >  --- a/drivers/acpi/acpi_processor.c
> >  +++ b/drivers/acpi/acpi_processor.c
> >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> >  acpi_device *device)
> >   	 *
> >   	 *  NOTE: Even if the processor has a cpuid, it may not be present
> >   	 *  because cpuid <-> apicid mapping is persistent now.
> >  +	 *
> >  +	 *  Note this allows 3 flows, it is up to the arch_register_cpu()
> >  +	 *  call to reject any that are not supported on a given architecture.
> >  +	 *  A) CPU becomes present.
> >  +	 *  B) Previously invalid logical CPU ID (Same as becoming present)
> >  +	 *  C) CPU already present and now being enabled (and wasn't
> >  registered
> >  +	 *     early on an arch that doesn't defer to here)
> >   	 */
> >  -	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> >  +	if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> >  +	     !get_cpu_device(pr->id)) ||
> >  +	    invalid_logical_cpuid(pr->id) ||
> >  +	    !cpu_present(pr->id)) {  
> 
> 
Hi Salil,

Thanks for quick review!

> Logic is clear but it is ugly. We should turn them into macro or inline.

You've found the 'ugly' in this approach vs keeping them separate.

For this version I wanted to keep it clear that indeed this condition
is a complex mess of different things (and to let people compare
it easily with the two paths in v5 to convinced themselves this
is the same) 

It's also a little tricky to do, so will need some thought.

I don't think a simple acpi_cpu_is_hotplug() condition is useful
as it just moves the complexity away from where a reader is looking
and it would only be used in this one case.

It doesn't separate well into finer grained subconditions because
(C) is a messy case of the vCPU HP case and a not done
something else earlier.  The disadvantage of only deferring for
arm64 and not other architectures.

The best I can quickly come up with is something like this:
#define acpi_cpu_not_present(cpu) \
	(invalid_logical_cpuid(cpu) || !cpu_present(cpu))
#define acpi_cpu_not_enabled(cpu) \
	(!invalid_logical_cpuid(cpu) || cpu_present(cpu))

	if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
	    acpi_cpu_not_present(pr->id))

Which would still need the same amount of documentation. The
code still isn't enough for me to immediately be able to see
what is going on.

So maybe worth it... I'm not sure.  Rafael, you get to keep this
fun, what would you prefer?

Jonathan


> 
> 
> Thanks
> Salil.

Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Rafael J. Wysocki]

On Wed, Apr 17, 2024 at 5:38 PM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Wed, 17 Apr 2024 16:03:51 +0100
> Salil Mehta <salil.mehta@huawei.com> wrote:
>
> > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > >
> > >  From: James Morse <james.morse@arm.com>
> > >
> > >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> > >  the ACPI interpreter is available and the _STA method can be evaluated.
> > >
> > >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> > >  Note that the arm64 specific call has not yet been added so for now this will
> > >  be called for the original hotplug case.
> > >
> > >  For architectures that do not defer until the ACPI Processor driver loads
> > >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> > >  present do not try to register again.
> > >
> > >  Systems can still be booted with 'acpi=off', or not include an ACPI
> > >  description at all as in these cases arch_register_cpu() will not have
> > >  deferred registration when first called.
> > >
> > >  This moves the CPU register logic back to a subsys_initcall(), while the
> > >  memory nodes will have been registered earlier.
> > >  Note this is where the call was prior to the cleanup series so there should be
> > >  no side effects of moving it back again for this specific case.
> > >
> > >  [PATCH 00/21] Initial cleanups for vCPU HP.
> > >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> > >
> > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> > >
> > >  Signed-off-by: James Morse <james.morse@arm.com>
> > >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> > >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> > >  ---
> > >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> > >      vCPU HP.
> > >  v5: Update commit message to make it clear this is moving the
> > >      init back to where it was until very recently.
> > >
> > >      No longer change the condition in the earlier registration point
> > >      as that will be handled by the arm64 registration routine
> > >      deferring until called again here.
> > >  ---
> > >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> > >   1 file changed, 11 insertions(+), 1 deletion(-)
> > >
> > >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > >  index 7ecb13775d7f..0cac77961020 100644
> > >  --- a/drivers/acpi/acpi_processor.c
> > >  +++ b/drivers/acpi/acpi_processor.c
> > >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> > >  acpi_device *device)
> > >      *
> > >      *  NOTE: Even if the processor has a cpuid, it may not be present
> > >      *  because cpuid <-> apicid mapping is persistent now.
> > >  +   *
> > >  +   *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > >  +   *  call to reject any that are not supported on a given architecture.
> > >  +   *  A) CPU becomes present.
> > >  +   *  B) Previously invalid logical CPU ID (Same as becoming present)
> > >  +   *  C) CPU already present and now being enabled (and wasn't
> > >  registered
> > >  +   *     early on an arch that doesn't defer to here)
> > >      */
> > >  -  if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > >  +  if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > >  +       !get_cpu_device(pr->id)) ||
> > >  +      invalid_logical_cpuid(pr->id) ||
> > >  +      !cpu_present(pr->id)) {
> >
> >
> Hi Salil,
>
> Thanks for quick review!
>
> > Logic is clear but it is ugly. We should turn them into macro or inline.
>
> You've found the 'ugly' in this approach vs keeping them separate.
>
> For this version I wanted to keep it clear that indeed this condition
> is a complex mess of different things (and to let people compare
> it easily with the two paths in v5 to convinced themselves this
> is the same)
>
> It's also a little tricky to do, so will need some thought.
>
> I don't think a simple acpi_cpu_is_hotplug() condition is useful
> as it just moves the complexity away from where a reader is looking
> and it would only be used in this one case.
>
> It doesn't separate well into finer grained subconditions because
> (C) is a messy case of the vCPU HP case and a not done
> something else earlier.  The disadvantage of only deferring for
> arm64 and not other architectures.
>
> The best I can quickly come up with is something like this:
> #define acpi_cpu_not_present(cpu) \
>         (invalid_logical_cpuid(cpu) || !cpu_present(cpu))
> #define acpi_cpu_not_enabled(cpu) \
>         (!invalid_logical_cpuid(cpu) || cpu_present(cpu))
>
>         if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
>             acpi_cpu_not_present(pr->id))
>
> Which would still need the same amount of documentation. The
> code still isn't enough for me to immediately be able to see
> what is going on.
>
> So maybe worth it... I'm not sure.  Rafael, you get to keep this
> fun, what would you prefer?

I would use a static inline function returning bool to carry out these
checks with comments explaining the different cases in which 'true'
needs to be returned.

RE: [PATCH v6 13/16] arm64: arch_register_cpu() variant to check if an ACPI handle is now available.

[Salil Mehta]

Hi Jonathan,

>  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  Sent: Wednesday, April 17, 2024 2:19 PM
>  
>  The ARM64 architecture does not support physical CPU HP today.
>  To avoid any possibility of a bug against such an architecture if defined in
>  future, check for the physical CPU HP case (not present) and return an error
>  on any such attempt.
>  
>  On ARM64 virtual CPU Hotplug relies on the status value that can be queried
>  via the AML method _STA for the CPU object.
>  
>  There are two conditions in which the CPU can be registered.
>  1) ACPI disabled.
>  2) ACPI enabled and the acpi_handle is available.
>     _STA evaluates to the CPU is both enabled and present.
>     (Note that in absence of the _STA method they are always in this
>      state).
>  
>  If neither of these conditions is met the CPU is not 'yet' ready to be used
>  and -EPROBE_DEFER is returned.
>  
>  Success occurs in the early attempt to register the CPUs if we are booting
>  with DT (no concept yet of vCPU HP) if not it succeeds for already enabled
>  CPUs when the ACPI Processor driver attaches to them.  Finally it may
>  succeed via the CPU Hotplug code indicating that the CPU is now enabled.
>  
>  For ACPI if CONFIG_ACPI_PROCESSOR the only path to get to
>  arch_register_cpu() with that handle set is via
>  acpi_processor_hot_add_init() which is only called from an ACPI bus scan in
>  which _STA has already been queried there is no need to repeat it here.
>  Add a comment to remind us of this in the future.
>  
>  Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
>  Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  ---
>  v6: Add protection again Physical CPU HP to the arch specific code
>      and don't actually check _STA
>  
>  Tested on arm64 with ACPI + DT build and DT only builds, booting with ACPI
>  and DT as appropriate.
>  ---
>   arch/arm64/kernel/smp.c | 53
>  +++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 53 insertions(+)
>  
>  diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index
>  dc0e0b3ec2d4..ccb6ad347df9 100644
>  --- a/arch/arm64/kernel/smp.c
>  +++ b/arch/arm64/kernel/smp.c
>  @@ -504,6 +504,59 @@ static int __init smp_cpu_setup(int cpu)  static bool
>  bootcpu_valid __initdata;  static unsigned int cpu_count = 1;
>  
>  +int arch_register_cpu(int cpu)
>  +{
>  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
>  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
>  +
>  +	if (!acpi_disabled && !acpi_handle &&
>  +	    IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
>  +		return -EPROBE_DEFER;
>  +
>  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
>  +	/* For now block anything that looks like physical CPU Hotplug */
>  +	if (invalid_logical_cpuid(cpu) || !cpu_present(cpu)) {
>  +		pr_err_once("Changing CPU present bit is not
>  supported\n");
>  +		return -ENODEV;
>  +	}
>  +#endif
>  +
>  +	/*
>  +	 * Availability of the acpi handle is sufficient to establish
>  +	 * that _STA has aleady been checked. No need to recheck here.
>  +	 */
>  +	c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
>  +


We would still need 'enabled' bitmask as applications need a way to clearly
get which processors are enabled and usable in case of ARM64. Otherwise,
they will end up scanning the entire MAX CPU space to figure out which
processors have been plugged or unplugged. It is inefficient to bank upon
errors to detect this and unnecessary to scan again and again.
           
+            set_cpu_enabled(cpu, true);   // will need this change


And its corresponding additions of enabled bitmask along side the present masks.

I think we had this discussion in Linaro Open Discussions group few years
back.


>  +	return register_cpu(c, cpu);
>  +}
>  +
>  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
>  +void arch_unregister_cpu(int cpu)
>  +{
>  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
>  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
>  +	acpi_status status;
>  +	unsigned long long sta;
>  +
>  +	if (!acpi_handle) {
>  +		pr_err_once("Removing a CPU without associated ACPI
>  handle\n");
>  +		return;
>  +	}
>  +
>  +	status = acpi_evaluate_integer(acpi_handle, "_STA", NULL, &sta);
>  +	if (ACPI_FAILURE(status))
>  +		return;
>  +
>  +	/* For now do not allow anything that looks like physical CPU HP */
>  +	if (cpu_present(cpu) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
>  +		pr_err_once("Changing CPU present bit is not
>  supported\n");
>  +		return;
>  +	}
>  +

For the same reasons as above:

+            set_cpu_enabled(cpu, flase);   // will need this change


>  +	unregister_cpu(c);
>  +}
>  +#endif /* CONFIG_ACPI_HOTPLUG_CPU */
>  +
>   #ifdef CONFIG_ACPI
>   static struct acpi_madt_generic_interrupt cpu_madt_gicc[NR_CPUS];
>  
>  --
>  2.39.2

Re: [PATCH v6 13/16] arm64: arch_register_cpu() variant to check if an ACPI handle is now available.

[Jonathan Cameron]

On Wed, 17 Apr 2024 17:33:02 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> Hi Jonathan,
> 
> >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> >  Sent: Wednesday, April 17, 2024 2:19 PM
> >  
> >  The ARM64 architecture does not support physical CPU HP today.
> >  To avoid any possibility of a bug against such an architecture if defined in
> >  future, check for the physical CPU HP case (not present) and return an error
> >  on any such attempt.
> >  
> >  On ARM64 virtual CPU Hotplug relies on the status value that can be queried
> >  via the AML method _STA for the CPU object.
> >  
> >  There are two conditions in which the CPU can be registered.
> >  1) ACPI disabled.
> >  2) ACPI enabled and the acpi_handle is available.
> >     _STA evaluates to the CPU is both enabled and present.
> >     (Note that in absence of the _STA method they are always in this
> >      state).
> >  
> >  If neither of these conditions is met the CPU is not 'yet' ready to be used
> >  and -EPROBE_DEFER is returned.
> >  
> >  Success occurs in the early attempt to register the CPUs if we are booting
> >  with DT (no concept yet of vCPU HP) if not it succeeds for already enabled
> >  CPUs when the ACPI Processor driver attaches to them.  Finally it may
> >  succeed via the CPU Hotplug code indicating that the CPU is now enabled.
> >  
> >  For ACPI if CONFIG_ACPI_PROCESSOR the only path to get to
> >  arch_register_cpu() with that handle set is via
> >  acpi_processor_hot_add_init() which is only called from an ACPI bus scan in
> >  which _STA has already been queried there is no need to repeat it here.
> >  Add a comment to remind us of this in the future.
> >  
> >  Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
> >  Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >  ---
> >  v6: Add protection again Physical CPU HP to the arch specific code
> >      and don't actually check _STA
> >  
> >  Tested on arm64 with ACPI + DT build and DT only builds, booting with ACPI
> >  and DT as appropriate.
> >  ---
> >   arch/arm64/kernel/smp.c | 53
> >  +++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 53 insertions(+)
> >  
> >  diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index
> >  dc0e0b3ec2d4..ccb6ad347df9 100644
> >  --- a/arch/arm64/kernel/smp.c
> >  +++ b/arch/arm64/kernel/smp.c
> >  @@ -504,6 +504,59 @@ static int __init smp_cpu_setup(int cpu)  static bool
> >  bootcpu_valid __initdata;  static unsigned int cpu_count = 1;
> >  
> >  +int arch_register_cpu(int cpu)
> >  +{
> >  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
> >  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
> >  +
> >  +	if (!acpi_disabled && !acpi_handle &&
> >  +	    IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
> >  +		return -EPROBE_DEFER;
> >  +
> >  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
> >  +	/* For now block anything that looks like physical CPU Hotplug */
> >  +	if (invalid_logical_cpuid(cpu) || !cpu_present(cpu)) {
> >  +		pr_err_once("Changing CPU present bit is not
> >  supported\n");
> >  +		return -ENODEV;
> >  +	}
> >  +#endif
> >  +
> >  +	/*
> >  +	 * Availability of the acpi handle is sufficient to establish
> >  +	 * that _STA has aleady been checked. No need to recheck here.
> >  +	 */
> >  +	c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
> >  +  
> 
> 
> We would still need 'enabled' bitmask as applications need a way to clearly
> get which processors are enabled and usable in case of ARM64. Otherwise,
> they will end up scanning the entire MAX CPU space to figure out which
> processors have been plugged or unplugged. It is inefficient to bank upon
> errors to detect this and unnecessary to scan again and again.
>            
> +            set_cpu_enabled(cpu, true);   // will need this change
> 
> 
> And its corresponding additions of enabled bitmask along side the present masks.
> 
> I think we had this discussion in Linaro Open Discussions group few years
> back.

Agreed - but if I understand correctly that is  handled in patch 16 -
which introduced the enabled bitmask. I tested that works and it all seems fine.
Done for all architectures in register_cpu() and unregister_cpu() rather
than in arch specific code.

Jonathan


> 
> 
> >  +	return register_cpu(c, cpu);
> >  +}
> >  +
> >  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
> >  +void arch_unregister_cpu(int cpu)
> >  +{
> >  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
> >  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
> >  +	acpi_status status;
> >  +	unsigned long long sta;
> >  +
> >  +	if (!acpi_handle) {
> >  +		pr_err_once("Removing a CPU without associated ACPI
> >  handle\n");
> >  +		return;
> >  +	}
> >  +
> >  +	status = acpi_evaluate_integer(acpi_handle, "_STA", NULL, &sta);
> >  +	if (ACPI_FAILURE(status))
> >  +		return;
> >  +
> >  +	/* For now do not allow anything that looks like physical CPU HP */
> >  +	if (cpu_present(cpu) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
> >  +		pr_err_once("Changing CPU present bit is not
> >  supported\n");
> >  +		return;
> >  +	}
> >  +  
> 
> For the same reasons as above:
> 
> +            set_cpu_enabled(cpu, flase);   // will need this change
> 
> 
> >  +	unregister_cpu(c);
> >  +}
> >  +#endif /* CONFIG_ACPI_HOTPLUG_CPU */
> >  +
> >   #ifdef CONFIG_ACPI
> >   static struct acpi_madt_generic_interrupt cpu_madt_gicc[NR_CPUS];
> >  
> >  --
> >  2.39.2  
> 

RE: [PATCH v6 16/16] cpumask: Add enabled cpumask for present CPUs that can be brought online

[Salil Mehta]

>  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  Sent: Wednesday, April 17, 2024 2:19 PM
>  
>  From: James Morse <james.morse@arm.com>
>  
>  The 'offline' file in sysfs shows all offline CPUs, including those that aren't
>  present. User-space is expected to remove not-present CPUs from this list
>  to learn which CPUs could be brought online.
>  
>  CPUs can be present but not-enabled. These CPUs can't be brought online
>  until the firmware policy changes, which comes with an ACPI notification
>  that will register the CPUs.
>  
>  With only the offline and present files, user-space is unable to determine
>  which CPUs it can try to bring online. Add a new CPU mask that shows this
>  based on all the registered CPUs.
>  
>  Signed-off-by: James Morse <james.morse@arm.com>
>  Tested-by: Miguel Luis <miguel.luis@oracle.com>
>  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
>  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
>  Acked-by: Thomas Gleixner <tglx@linutronix.de>
>  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
>  Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  
>  ---
>  v5: No change
>  ---
>   .../ABI/testing/sysfs-devices-system-cpu      |  6 +++++
>   drivers/base/cpu.c                            | 10 ++++++++
>   include/linux/cpumask.h                       | 25 +++++++++++++++++++
>   kernel/cpu.c                                  |  3 +++
>   4 files changed, 44 insertions(+)
>  

[...]


>  diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index
>  b9d0d14e5960..4713b86d20f2 100644
>  --- a/drivers/base/cpu.c
>  +++ b/drivers/base/cpu.c
>  @@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)  {
>   	int logical_cpu = cpu->dev.id;
>  
>  +	set_cpu_enabled(logical_cpu, false);


sorry, It is being done here in context to (un)register)cpu().


>   	unregister_cpu_under_node(logical_cpu,
>  cpu_to_node(logical_cpu));
>  
>   	device_unregister(&cpu->dev);
>  @@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
>  }  static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
>  
>  +static ssize_t print_cpus_enabled(struct device *dev,
>  +				  struct device_attribute *attr, char *buf) {
>  +	return sysfs_emit(buf, "%*pbl\n",
>  cpumask_pr_args(cpu_enabled_mask));
>  +}
>  +static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);
>  +
>   static ssize_t print_cpus_isolated(struct device *dev,
>   				  struct device_attribute *attr, char *buf)  {
>  @@ -413,6 +421,7 @@ int register_cpu(struct cpu *cpu, int num)
>   	register_cpu_under_node(num, cpu_to_node(num));
>   	dev_pm_qos_expose_latency_limit(&cpu->dev,
>  
>  	PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
>  +	set_cpu_enabled(num, true);


and here.

Thanks
Salil.

RE: [PATCH v6 13/16] arm64: arch_register_cpu() variant to check if an ACPI handle is now available.

[Salil Mehta]

>  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  Sent: Wednesday, April 17, 2024 5:55 PM
>  
>  On Wed, 17 Apr 2024 17:33:02 +0100
>  Salil Mehta <salil.mehta@huawei.com> wrote:
>  
>  > Hi Jonathan,
>  >
>  > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
>  > >  Sent: Wednesday, April 17, 2024 2:19 PM
>  > >
>  > >  The ARM64 architecture does not support physical CPU HP today.
>  > >  To avoid any possibility of a bug against such an architecture if
>  > > defined in  future, check for the physical CPU HP case (not present)
>  > > and return an error  on any such attempt.
>  > >
>  > >  On ARM64 virtual CPU Hotplug relies on the status value that can be
>  > > queried  via the AML method _STA for the CPU object.
>  > >
>  > >  There are two conditions in which the CPU can be registered.
>  > >  1) ACPI disabled.
>  > >  2) ACPI enabled and the acpi_handle is available.
>  > >     _STA evaluates to the CPU is both enabled and present.
>  > >     (Note that in absence of the _STA method they are always in this
>  > >      state).
>  > >
>  > >  If neither of these conditions is met the CPU is not 'yet' ready to
>  > > be used  and -EPROBE_DEFER is returned.
>  > >
>  > >  Success occurs in the early attempt to register the CPUs if we are
>  > > booting  with DT (no concept yet of vCPU HP) if not it succeeds for
>  > > already enabled  CPUs when the ACPI Processor driver attaches to
>  > > them.  Finally it may  succeed via the CPU Hotplug code indicating that
>  the CPU is now enabled.
>  > >
>  > >  For ACPI if CONFIG_ACPI_PROCESSOR the only path to get to
>  > >  arch_register_cpu() with that handle set is via
>  > >  acpi_processor_hot_add_init() which is only called from an ACPI bus
>  > > scan in  which _STA has already been queried there is no need to repeat
>  it here.
>  > >  Add a comment to remind us of this in the future.
>  > >
>  > >  Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
>  > >  Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  > >  ---
>  > >  v6: Add protection again Physical CPU HP to the arch specific code
>  > >      and don't actually check _STA
>  > >
>  > >  Tested on arm64 with ACPI + DT build and DT only builds, booting
>  > > with ACPI  and DT as appropriate.
>  > >  ---
>  > >   arch/arm64/kernel/smp.c | 53
>  > >  +++++++++++++++++++++++++++++++++++++++++
>  > >   1 file changed, 53 insertions(+)
>  > >
>  > >  diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>  > > index
>  > >  dc0e0b3ec2d4..ccb6ad347df9 100644
>  > >  --- a/arch/arm64/kernel/smp.c
>  > >  +++ b/arch/arm64/kernel/smp.c
>  > >  @@ -504,6 +504,59 @@ static int __init smp_cpu_setup(int cpu)
>  > > static bool  bootcpu_valid __initdata;  static unsigned int
>  > > cpu_count = 1;
>  > >
>  > >  +int arch_register_cpu(int cpu)
>  > >  +{
>  > >  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
>  > >  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
>  > >  +
>  > >  +	if (!acpi_disabled && !acpi_handle &&
>  > >  +	    IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
>  > >  +		return -EPROBE_DEFER;
>  > >  +
>  > >  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
>  > >  +	/* For now block anything that looks like physical CPU Hotplug */
>  > >  +	if (invalid_logical_cpuid(cpu) || !cpu_present(cpu)) {
>  > >  +		pr_err_once("Changing CPU present bit is not
>  > >  supported\n");
>  > >  +		return -ENODEV;
>  > >  +	}
>  > >  +#endif
>  > >  +
>  > >  +	/*
>  > >  +	 * Availability of the acpi handle is sufficient to establish
>  > >  +	 * that _STA has aleady been checked. No need to recheck here.
>  > >  +	 */
>  > >  +	c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
>  > >  +
>  >
>  >
>  > We would still need 'enabled' bitmask as applications need a way to
>  > clearly get which processors are enabled and usable in case of ARM64.
>  > Otherwise, they will end up scanning the entire MAX CPU space to
>  > figure out which processors have been plugged or unplugged. It is
>  > inefficient to bank upon errors to detect this and unnecessary to scan
>  again and again.
>  >
>  > +            set_cpu_enabled(cpu, true);   // will need this change
>  >
>  >
>  > And its corresponding additions of enabled bitmask along side the present
>  masks.
>  >
>  > I think we had this discussion in Linaro Open Discussions group few
>  > years back.
>  
>  Agreed - but if I understand correctly that is  handled in patch 16 - which
>  introduced the enabled bitmask. I tested that works and it all seems fine.
>  Done for all architectures in register_cpu() and unregister_cpu() rather than
>  in arch specific code.


Sorry, I missed that. Yes, this logic is already present in later patches.


Thanks
Salil.


>  
>  Jonathan
>  
>  
>  >
>  >
>  > >  +	return register_cpu(c, cpu);
>  > >  +}
>  > >  +
>  > >  +#ifdef CONFIG_ACPI_HOTPLUG_CPU
>  > >  +void arch_unregister_cpu(int cpu)
>  > >  +{
>  > >  +	acpi_handle acpi_handle = acpi_get_processor_handle(cpu);
>  > >  +	struct cpu *c = &per_cpu(cpu_devices, cpu);
>  > >  +	acpi_status status;
>  > >  +	unsigned long long sta;
>  > >  +
>  > >  +	if (!acpi_handle) {
>  > >  +		pr_err_once("Removing a CPU without associated ACPI
>  > >  handle\n");
>  > >  +		return;
>  > >  +	}
>  > >  +
>  > >  +	status = acpi_evaluate_integer(acpi_handle, "_STA", NULL, &sta);
>  > >  +	if (ACPI_FAILURE(status))
>  > >  +		return;
>  > >  +
>  > >  +	/* For now do not allow anything that looks like physical CPU HP */
>  > >  +	if (cpu_present(cpu) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
>  > >  +		pr_err_once("Changing CPU present bit is not
>  > >  supported\n");
>  > >  +		return;
>  > >  +	}
>  > >  +
>  >
>  > For the same reasons as above:
>  >
>  > +            set_cpu_enabled(cpu, flase);   // will need this change
>  >
>  >
>  > >  +	unregister_cpu(c);
>  > >  +}
>  > >  +#endif /* CONFIG_ACPI_HOTPLUG_CPU */  +
>  > >   #ifdef CONFIG_ACPI
>  > >   static struct acpi_madt_generic_interrupt cpu_madt_gicc[NR_CPUS];
>  > >
>  > >  --
>  > >  2.39.2
>  >

Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Jonathan Cameron]

On Wed, 17 Apr 2024 17:59:36 +0200
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Wed, Apr 17, 2024 at 5:38 PM Jonathan Cameron
> <Jonathan.Cameron@huawei.com> wrote:
> >
> > On Wed, 17 Apr 2024 16:03:51 +0100
> > Salil Mehta <salil.mehta@huawei.com> wrote:
> >  
> > > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > > >
> > > >  From: James Morse <james.morse@arm.com>
> > > >
> > > >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> > > >  the ACPI interpreter is available and the _STA method can be evaluated.
> > > >
> > > >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> > > >  Note that the arm64 specific call has not yet been added so for now this will
> > > >  be called for the original hotplug case.
> > > >
> > > >  For architectures that do not defer until the ACPI Processor driver loads
> > > >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> > > >  present do not try to register again.
> > > >
> > > >  Systems can still be booted with 'acpi=off', or not include an ACPI
> > > >  description at all as in these cases arch_register_cpu() will not have
> > > >  deferred registration when first called.
> > > >
> > > >  This moves the CPU register logic back to a subsys_initcall(), while the
> > > >  memory nodes will have been registered earlier.
> > > >  Note this is where the call was prior to the cleanup series so there should be
> > > >  no side effects of moving it back again for this specific case.
> > > >
> > > >  [PATCH 00/21] Initial cleanups for vCPU HP.
> > > >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> > > >
> > > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> > > >
> > > >  Signed-off-by: James Morse <james.morse@arm.com>
> > > >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> > > >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> > > >  ---
> > > >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> > > >      vCPU HP.
> > > >  v5: Update commit message to make it clear this is moving the
> > > >      init back to where it was until very recently.
> > > >
> > > >      No longer change the condition in the earlier registration point
> > > >      as that will be handled by the arm64 registration routine
> > > >      deferring until called again here.
> > > >  ---
> > > >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> > > >   1 file changed, 11 insertions(+), 1 deletion(-)
> > > >
> > > >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > >  index 7ecb13775d7f..0cac77961020 100644
> > > >  --- a/drivers/acpi/acpi_processor.c
> > > >  +++ b/drivers/acpi/acpi_processor.c
> > > >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> > > >  acpi_device *device)
> > > >      *
> > > >      *  NOTE: Even if the processor has a cpuid, it may not be present
> > > >      *  because cpuid <-> apicid mapping is persistent now.
> > > >  +   *
> > > >  +   *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > > >  +   *  call to reject any that are not supported on a given architecture.
> > > >  +   *  A) CPU becomes present.
> > > >  +   *  B) Previously invalid logical CPU ID (Same as becoming present)
> > > >  +   *  C) CPU already present and now being enabled (and wasn't
> > > >  registered
> > > >  +   *     early on an arch that doesn't defer to here)
> > > >      */
> > > >  -  if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > >  +  if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > > >  +       !get_cpu_device(pr->id)) ||
> > > >  +      invalid_logical_cpuid(pr->id) ||
> > > >  +      !cpu_present(pr->id)) {  
> > >
> > >  
> > Hi Salil,
> >
> > Thanks for quick review!
> >  
> > > Logic is clear but it is ugly. We should turn them into macro or inline.  
> >
> > You've found the 'ugly' in this approach vs keeping them separate.
> >
> > For this version I wanted to keep it clear that indeed this condition
> > is a complex mess of different things (and to let people compare
> > it easily with the two paths in v5 to convinced themselves this
> > is the same)
> >
> > It's also a little tricky to do, so will need some thought.
> >
> > I don't think a simple acpi_cpu_is_hotplug() condition is useful
> > as it just moves the complexity away from where a reader is looking
> > and it would only be used in this one case.
> >
> > It doesn't separate well into finer grained subconditions because
> > (C) is a messy case of the vCPU HP case and a not done
> > something else earlier.  The disadvantage of only deferring for
> > arm64 and not other architectures.
> >
> > The best I can quickly come up with is something like this:
> > #define acpi_cpu_not_present(cpu) \
> >         (invalid_logical_cpuid(cpu) || !cpu_present(cpu))
> > #define acpi_cpu_not_enabled(cpu) \
> >         (!invalid_logical_cpuid(cpu) || cpu_present(cpu))
> >
> >         if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
> >             acpi_cpu_not_present(pr->id))
> >
> > Which would still need the same amount of documentation. The
> > code still isn't enough for me to immediately be able to see
> > what is going on.
> >
> > So maybe worth it... I'm not sure.  Rafael, you get to keep this
> > fun, what would you prefer?  
> 
> I would use a static inline function returning bool to carry out these
> checks with comments explaining the different cases in which 'true'
> needs to be returned.

The following makes a subtle logic change (I'll retest tomorrow) but
I think that get_cpu_device(cpu) can never succeed in a path where
hotadd makes sense. 

+/*
+ * Identify if the state transition indicates that hotadd_init
+ * should be called.
+ *
+ * For acpi_processor_add() to be called, the reported state must
+ * now be enabled and present. Conditions reflect prior state.
+ */
+static inline bool acpi_processor_should_hotadd_init(int cpu)
+{
+       /* Already register, initial registration was not deferred */
+       if (get_cpu_device(cpu))
+               return false;
+
+       /* Processor has become present */
+       if (!cpu_present(cpu))
+               return true;
+
+       /* Logical cpuid currently invalid indicates hotadd */
+       if (invalid_logical_cpuid(cpu))
+               return true;
+
+       /*
+        * Previously present and the logical cpu id is valid.
+	 * Deferred registration now _STA can be queries, or
+        * Hotadd due to enabled becoming true on an online capable
+        * CPU.
+        */
+       if (cpu_present(cpu))
+               return true;
+
+       return false;
+}
+
 static int acpi_processor_get_info(struct acpi_device *device)
 {
        union acpi_object object = { 0 };
@@ -356,18 +388,8 @@ static int acpi_processor_get_info(struct acpi_device *device)
         *
         *  NOTE: Even if the processor has a cpuid, it may not be present
         *  because cpuid <-> apicid mapping is persistent now.
-        *
-        *  Note this allows 3 flows, it is up to the arch_register_cpu()
-        *  call to reject any that are not supported on a given architecture.
-        *  A) CPU becomes present.
-        *  B) Previously invalid logical CPU ID (Same as becoming present)
-        *  C) CPU already present and now being enabled (and wasn't registered
-        *     early on an arch that doesn't defer to here)
         */
-       if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
-            !get_cpu_device(pr->id)) ||
-           invalid_logical_cpuid(pr->id) ||
-           !cpu_present(pr->id)) {
+       if (acpi_processor_should_hotadd_init(pr->id)) {
                ret = acpi_processor_hotadd_init(pr, device);

Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Rafael J. Wysocki]

On Wed, Apr 17, 2024 at 7:09 PM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Wed, 17 Apr 2024 17:59:36 +0200
> "Rafael J. Wysocki" <rafael@kernel.org> wrote:
>
> > On Wed, Apr 17, 2024 at 5:38 PM Jonathan Cameron
> > <Jonathan.Cameron@huawei.com> wrote:
> > >
> > > On Wed, 17 Apr 2024 16:03:51 +0100
> > > Salil Mehta <salil.mehta@huawei.com> wrote:
> > >
> > > > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > > > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > > > >
> > > > >  From: James Morse <james.morse@arm.com>
> > > > >
> > > > >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> > > > >  the ACPI interpreter is available and the _STA method can be evaluated.
> > > > >
> > > > >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> > > > >  Note that the arm64 specific call has not yet been added so for now this will
> > > > >  be called for the original hotplug case.
> > > > >
> > > > >  For architectures that do not defer until the ACPI Processor driver loads
> > > > >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> > > > >  present do not try to register again.
> > > > >
> > > > >  Systems can still be booted with 'acpi=off', or not include an ACPI
> > > > >  description at all as in these cases arch_register_cpu() will not have
> > > > >  deferred registration when first called.
> > > > >
> > > > >  This moves the CPU register logic back to a subsys_initcall(), while the
> > > > >  memory nodes will have been registered earlier.
> > > > >  Note this is where the call was prior to the cleanup series so there should be
> > > > >  no side effects of moving it back again for this specific case.
> > > > >
> > > > >  [PATCH 00/21] Initial cleanups for vCPU HP.
> > > > >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> > > > >
> > > > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> > > > >
> > > > >  Signed-off-by: James Morse <james.morse@arm.com>
> > > > >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> > > > >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > > >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > > >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > > > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> > > > >  ---
> > > > >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> > > > >      vCPU HP.
> > > > >  v5: Update commit message to make it clear this is moving the
> > > > >      init back to where it was until very recently.
> > > > >
> > > > >      No longer change the condition in the earlier registration point
> > > > >      as that will be handled by the arm64 registration routine
> > > > >      deferring until called again here.
> > > > >  ---
> > > > >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> > > > >   1 file changed, 11 insertions(+), 1 deletion(-)
> > > > >
> > > > >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > > >  index 7ecb13775d7f..0cac77961020 100644
> > > > >  --- a/drivers/acpi/acpi_processor.c
> > > > >  +++ b/drivers/acpi/acpi_processor.c
> > > > >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> > > > >  acpi_device *device)
> > > > >      *
> > > > >      *  NOTE: Even if the processor has a cpuid, it may not be present
> > > > >      *  because cpuid <-> apicid mapping is persistent now.
> > > > >  +   *
> > > > >  +   *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > > > >  +   *  call to reject any that are not supported on a given architecture.
> > > > >  +   *  A) CPU becomes present.
> > > > >  +   *  B) Previously invalid logical CPU ID (Same as becoming present)
> > > > >  +   *  C) CPU already present and now being enabled (and wasn't
> > > > >  registered
> > > > >  +   *     early on an arch that doesn't defer to here)
> > > > >      */
> > > > >  -  if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > > >  +  if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > > > >  +       !get_cpu_device(pr->id)) ||
> > > > >  +      invalid_logical_cpuid(pr->id) ||
> > > > >  +      !cpu_present(pr->id)) {
> > > >
> > > >
> > > Hi Salil,
> > >
> > > Thanks for quick review!
> > >
> > > > Logic is clear but it is ugly. We should turn them into macro or inline.
> > >
> > > You've found the 'ugly' in this approach vs keeping them separate.
> > >
> > > For this version I wanted to keep it clear that indeed this condition
> > > is a complex mess of different things (and to let people compare
> > > it easily with the two paths in v5 to convinced themselves this
> > > is the same)
> > >
> > > It's also a little tricky to do, so will need some thought.
> > >
> > > I don't think a simple acpi_cpu_is_hotplug() condition is useful
> > > as it just moves the complexity away from where a reader is looking
> > > and it would only be used in this one case.
> > >
> > > It doesn't separate well into finer grained subconditions because
> > > (C) is a messy case of the vCPU HP case and a not done
> > > something else earlier.  The disadvantage of only deferring for
> > > arm64 and not other architectures.
> > >
> > > The best I can quickly come up with is something like this:
> > > #define acpi_cpu_not_present(cpu) \
> > >         (invalid_logical_cpuid(cpu) || !cpu_present(cpu))
> > > #define acpi_cpu_not_enabled(cpu) \
> > >         (!invalid_logical_cpuid(cpu) || cpu_present(cpu))
> > >
> > >         if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
> > >             acpi_cpu_not_present(pr->id))
> > >
> > > Which would still need the same amount of documentation. The
> > > code still isn't enough for me to immediately be able to see
> > > what is going on.
> > >
> > > So maybe worth it... I'm not sure.  Rafael, you get to keep this
> > > fun, what would you prefer?
> >
> > I would use a static inline function returning bool to carry out these
> > checks with comments explaining the different cases in which 'true'
> > needs to be returned.
>
> The following makes a subtle logic change (I'll retest tomorrow) but
> I think that get_cpu_device(cpu) can never succeed in a path where
> hotadd makes sense.
>
> +/*
> + * Identify if the state transition indicates that hotadd_init
> + * should be called.
> + *
> + * For acpi_processor_add() to be called, the reported state must
> + * now be enabled and present. Conditions reflect prior state.
> + */
> +static inline bool acpi_processor_should_hotadd_init(int cpu)
> +{
> +       /* Already register, initial registration was not deferred */

"Already registered." I think.

> +       if (get_cpu_device(cpu))
> +               return false;
> +
> +       /* Processor has become present */
> +       if (!cpu_present(cpu))
> +               return true;
> +
> +       /* Logical cpuid currently invalid indicates hotadd */
> +       if (invalid_logical_cpuid(cpu))
> +               return true;
> +
> +       /*
> +        * Previously present and the logical cpu id is valid.
> +        * Deferred registration now _STA can be queries, or
> +        * Hotadd due to enabled becoming true on an online capable
> +        * CPU.
> +        */
> +       if (cpu_present(cpu))
> +               return true;

It returns true for both the cpu_present(cpu) and !cpu_present(cpu)
cases, so will it ever return false except for when
get_cpu_device(cpu) returns true?

> +
> +       return false;
> +}
> +
>  static int acpi_processor_get_info(struct acpi_device *device)
>  {
>         union acpi_object object = { 0 };
> @@ -356,18 +388,8 @@ static int acpi_processor_get_info(struct acpi_device *device)
>          *
>          *  NOTE: Even if the processor has a cpuid, it may not be present
>          *  because cpuid <-> apicid mapping is persistent now.
> -        *
> -        *  Note this allows 3 flows, it is up to the arch_register_cpu()
> -        *  call to reject any that are not supported on a given architecture.
> -        *  A) CPU becomes present.
> -        *  B) Previously invalid logical CPU ID (Same as becoming present)
> -        *  C) CPU already present and now being enabled (and wasn't registered
> -        *     early on an arch that doesn't defer to here)
>          */
> -       if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> -            !get_cpu_device(pr->id)) ||
> -           invalid_logical_cpuid(pr->id) ||
> -           !cpu_present(pr->id)) {
> +       if (acpi_processor_should_hotadd_init(pr->id)) {
>                 ret = acpi_processor_hotadd_init(pr, device);
>

Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Jonathan Cameron]

On Wed, 17 Apr 2024 19:59:50 +0200
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Wed, Apr 17, 2024 at 7:09 PM Jonathan Cameron
> <Jonathan.Cameron@huawei.com> wrote:
> >
> > On Wed, 17 Apr 2024 17:59:36 +0200
> > "Rafael J. Wysocki" <rafael@kernel.org> wrote:
> >  
> > > On Wed, Apr 17, 2024 at 5:38 PM Jonathan Cameron
> > > <Jonathan.Cameron@huawei.com> wrote:  
> > > >
> > > > On Wed, 17 Apr 2024 16:03:51 +0100
> > > > Salil Mehta <salil.mehta@huawei.com> wrote:
> > > >  
> > > > > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > > > > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > > > > >
> > > > > >  From: James Morse <james.morse@arm.com>
> > > > > >
> > > > > >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> > > > > >  the ACPI interpreter is available and the _STA method can be evaluated.
> > > > > >
> > > > > >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> > > > > >  Note that the arm64 specific call has not yet been added so for now this will
> > > > > >  be called for the original hotplug case.
> > > > > >
> > > > > >  For architectures that do not defer until the ACPI Processor driver loads
> > > > > >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> > > > > >  present do not try to register again.
> > > > > >
> > > > > >  Systems can still be booted with 'acpi=off', or not include an ACPI
> > > > > >  description at all as in these cases arch_register_cpu() will not have
> > > > > >  deferred registration when first called.
> > > > > >
> > > > > >  This moves the CPU register logic back to a subsys_initcall(), while the
> > > > > >  memory nodes will have been registered earlier.
> > > > > >  Note this is where the call was prior to the cleanup series so there should be
> > > > > >  no side effects of moving it back again for this specific case.
> > > > > >
> > > > > >  [PATCH 00/21] Initial cleanups for vCPU HP.
> > > > > >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> > > > > >
> > > > > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> > > > > >
> > > > > >  Signed-off-by: James Morse <james.morse@arm.com>
> > > > > >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> > > > > >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > > > >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > > > >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > > > > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > > > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> > > > > >  ---
> > > > > >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> > > > > >      vCPU HP.
> > > > > >  v5: Update commit message to make it clear this is moving the
> > > > > >      init back to where it was until very recently.
> > > > > >
> > > > > >      No longer change the condition in the earlier registration point
> > > > > >      as that will be handled by the arm64 registration routine
> > > > > >      deferring until called again here.
> > > > > >  ---
> > > > > >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> > > > > >   1 file changed, 11 insertions(+), 1 deletion(-)
> > > > > >
> > > > > >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > > > >  index 7ecb13775d7f..0cac77961020 100644
> > > > > >  --- a/drivers/acpi/acpi_processor.c
> > > > > >  +++ b/drivers/acpi/acpi_processor.c
> > > > > >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> > > > > >  acpi_device *device)
> > > > > >      *
> > > > > >      *  NOTE: Even if the processor has a cpuid, it may not be present
> > > > > >      *  because cpuid <-> apicid mapping is persistent now.
> > > > > >  +   *
> > > > > >  +   *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > > > > >  +   *  call to reject any that are not supported on a given architecture.
> > > > > >  +   *  A) CPU becomes present.
> > > > > >  +   *  B) Previously invalid logical CPU ID (Same as becoming present)
> > > > > >  +   *  C) CPU already present and now being enabled (and wasn't
> > > > > >  registered
> > > > > >  +   *     early on an arch that doesn't defer to here)
> > > > > >      */
> > > > > >  -  if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > > > >  +  if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > > > > >  +       !get_cpu_device(pr->id)) ||
> > > > > >  +      invalid_logical_cpuid(pr->id) ||
> > > > > >  +      !cpu_present(pr->id)) {  
> > > > >
> > > > >  
> > > > Hi Salil,
> > > >
> > > > Thanks for quick review!
> > > >  
> > > > > Logic is clear but it is ugly. We should turn them into macro or inline.  
> > > >
> > > > You've found the 'ugly' in this approach vs keeping them separate.
> > > >
> > > > For this version I wanted to keep it clear that indeed this condition
> > > > is a complex mess of different things (and to let people compare
> > > > it easily with the two paths in v5 to convinced themselves this
> > > > is the same)
> > > >
> > > > It's also a little tricky to do, so will need some thought.
> > > >
> > > > I don't think a simple acpi_cpu_is_hotplug() condition is useful
> > > > as it just moves the complexity away from where a reader is looking
> > > > and it would only be used in this one case.
> > > >
> > > > It doesn't separate well into finer grained subconditions because
> > > > (C) is a messy case of the vCPU HP case and a not done
> > > > something else earlier.  The disadvantage of only deferring for
> > > > arm64 and not other architectures.
> > > >
> > > > The best I can quickly come up with is something like this:
> > > > #define acpi_cpu_not_present(cpu) \
> > > >         (invalid_logical_cpuid(cpu) || !cpu_present(cpu))
> > > > #define acpi_cpu_not_enabled(cpu) \
> > > >         (!invalid_logical_cpuid(cpu) || cpu_present(cpu))
> > > >
> > > >         if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
> > > >             acpi_cpu_not_present(pr->id))
> > > >
> > > > Which would still need the same amount of documentation. The
> > > > code still isn't enough for me to immediately be able to see
> > > > what is going on.
> > > >
> > > > So maybe worth it... I'm not sure.  Rafael, you get to keep this
> > > > fun, what would you prefer?  
> > >
> > > I would use a static inline function returning bool to carry out these
> > > checks with comments explaining the different cases in which 'true'
> > > needs to be returned.  
> >
> > The following makes a subtle logic change (I'll retest tomorrow) but
> > I think that get_cpu_device(cpu) can never succeed in a path where
> > hotadd makes sense.
> >
> > +/*
> > + * Identify if the state transition indicates that hotadd_init
> > + * should be called.
> > + *
> > + * For acpi_processor_add() to be called, the reported state must
> > + * now be enabled and present. Conditions reflect prior state.
> > + */
> > +static inline bool acpi_processor_should_hotadd_init(int cpu)
> > +{
> > +       /* Already register, initial registration was not deferred */  
> 
> "Already registered." I think.
> 
> > +       if (get_cpu_device(cpu))
> > +               return false;
> > +
> > +       /* Processor has become present */
> > +       if (!cpu_present(cpu))
> > +               return true;
> > +
> > +       /* Logical cpuid currently invalid indicates hotadd */
> > +       if (invalid_logical_cpuid(cpu))
> > +               return true;
> > +
> > +       /*
> > +        * Previously present and the logical cpu id is valid.
> > +        * Deferred registration now _STA can be queries, or
> > +        * Hotadd due to enabled becoming true on an online capable
> > +        * CPU.
> > +        */
> > +       if (cpu_present(cpu))
> > +               return true;  
> 
> It returns true for both the cpu_present(cpu) and !cpu_present(cpu)
> cases, so will it ever return false except for when
> get_cpu_device(cpu) returns true?

It indeed looks suspicious. My logic is probably wrong.  Will check
- I guess maybe pulling out the get_cpu_device(cpu) indeed flattens
this as you point out. Kind of makes sense if true.

Jonathan

> 
> > +
> > +       return false;
> > +}
> > +
> >  static int acpi_processor_get_info(struct acpi_device *device)
> >  {
> >         union acpi_object object = { 0 };
> > @@ -356,18 +388,8 @@ static int acpi_processor_get_info(struct acpi_device *device)
> >          *
> >          *  NOTE: Even if the processor has a cpuid, it may not be present
> >          *  because cpuid <-> apicid mapping is persistent now.
> > -        *
> > -        *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > -        *  call to reject any that are not supported on a given architecture.
> > -        *  A) CPU becomes present.
> > -        *  B) Previously invalid logical CPU ID (Same as becoming present)
> > -        *  C) CPU already present and now being enabled (and wasn't registered
> > -        *     early on an arch that doesn't defer to here)
> >          */
> > -       if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > -            !get_cpu_device(pr->id)) ||
> > -           invalid_logical_cpuid(pr->id) ||
> > -           !cpu_present(pr->id)) {
> > +       if (acpi_processor_should_hotadd_init(pr->id)) {
> >                 ret = acpi_processor_hotadd_init(pr, device);
> >  

Re: [PATCH v6 04/16] ACPI: processor: Move checks and availability of acpi_processor earlier

[Jonathan Cameron]

On Wed, 17 Apr 2024 14:18:57 +0100
Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:

> Make the per_cpu(processors, cpu) entries available earlier so that
> they are available in arch_register_cpu() as ARM64 will need access
> to the acpi_handle to distinguish between acpi_processor_add()
> and earlier registration attempts (which will fail as _STA cannot
> be checked).
> 
> Reorder the remove flow to clear this per_cpu() after
> arch_unregister_cpu() has completed, allowing it to be used in
> there as well.
> 
> Note that on x86 for the CPU hotplug case, the pr->id prior to
> acpi_map_cpu() may be invalid. Thus the per_cpu() structures
> must be initialized after that call or after checking the ID
> is valid (not hotplug path).
> 
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> v6: As per discussion in v5 thread, don't use the cpu->dev and
>     make this data available earlier by moving the assignment checks
>     int acpi_processor_get_info().
> ---
>  drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++--------------
>  1 file changed, 47 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index ba0a6f0ac841..2c164451ab53 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -184,7 +184,35 @@ static void __init acpi_pcc_cpufreq_init(void) {}
>  
>  /* Initialization */
>  #ifdef CONFIG_ACPI_HOTPLUG_CPU
Note I messed up a rebase here.  This ifdef should come after the new function
(see later)

Will fix for v7.
> -static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> +static DEFINE_PER_CPU(void *, processor_device_array);
> +
> +static void acpi_processor_set_per_cpu(struct acpi_processor *pr,
> +				       struct acpi_device *device)
> +{
> +	BUG_ON(pr->id >= nr_cpu_ids);
> +	/*
> +	 * Buggy BIOS check.
> +	 * ACPI id of processors can be reported wrongly by the BIOS.
> +	 * Don't trust it blindly
> +	 */
> +	if (per_cpu(processor_device_array, pr->id) != NULL &&
> +	    per_cpu(processor_device_array, pr->id) != device) {
> +		dev_warn(&device->dev,
> +			 "BIOS reported wrong ACPI id %d for the processor\n",
> +			 pr->id);
> +		/* Give up, but do not abort the namespace scan. */
> +		return;
> +	}
> +	/*
> +	 * processor_device_array is not cleared on errors to allow buggy BIOS
> +	 * checks.
> +	 */
> +	per_cpu(processor_device_array, pr->id) = device;
> +	per_cpu(processors, pr->id) = pr;
> +}
> +

The ifdef should be here as...

> +static int acpi_processor_hotadd_init(struct acpi_processor *pr,
> +				      struct acpi_device *device)
>  {
>  	int ret;
>  
> @@ -198,6 +226,8 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>  	if (ret)
>  		goto out;
>  
> +	acpi_processor_set_per_cpu(pr, device);
> +
>  	ret = arch_register_cpu(pr->id);
>  	if (ret) {
>  		acpi_unmap_cpu(pr->id);
> @@ -217,7 +247,8 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>  	return ret;
>  }
>  #else
> -static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
> +static inline int acpi_processor_hotadd_init(struct acpi_processor *pr,
> +					     struct acpi_device *device)
>  {
>  	return -ENODEV;
>  }
> @@ -232,6 +263,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
>  	acpi_status status = AE_OK;
>  	static int cpu0_initialized;
>  	unsigned long long value;
> +	int ret;
>  
>  	acpi_processor_errata();
>  
> @@ -316,10 +348,12 @@ static int acpi_processor_get_info(struct acpi_device *device)
>  	 *  because cpuid <-> apicid mapping is persistent now.
>  	 */
>  	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> -		int ret = acpi_processor_hotadd_init(pr);
> +		ret = acpi_processor_hotadd_init(pr, device);
>  
>  		if (ret)
> -			return ret;
> +			goto err;
> +	} else {
> +		acpi_processor_set_per_cpu(pr, device);

This is not covered by CONFIG_ACPI_HOTPLUG_CPU

>  	}