[PATCH v2 0/5] CPPC/amd-pstate: Fixes to limit actions to online CPUs

[PATCH v2 0/5] CPPC/amd-pstate: Fixes to limit actions to online CPUs

[Gautham R. Shenoy]

Hello,

This is the v2 of the patchset to restrict certain actions to only
online CPUs instead of present CPUs.

The v1 of this patchset can be found here:
https://lore.kernel.org/lkml/20251105143851.4251-1-gautham.shenoy@amd.com/

Changes between v1 --> v2:

 * Picked up the Reviewed-by tags from Mario for the first four
   patches
 
 * Picked up the Tested-by tags from Chris for the first two patches
 
 * Added a fifth patch to fix calling of cppc_set_auto_sel() for only
   online CPUs in the amd-pstate driver code (Mario)


Gautham R. Shenoy (5):
  ACPI: CPPC: Detect preferred core availability on online CPUs
  ACPI: CPPC: Check _CPC validity for only the online CPUs
  ACPI: CPPC: Perform fast check switch only for online CPUs
  ACPI: CPPC: Limit perf ctrs in PCC check only to online CPUs
  cpufreq/amd-pstate: Call cppc_set_auto_sel() only for online CPUs

 arch/x86/kernel/acpi/cppc.c  | 2 +-
 drivers/acpi/cppc_acpi.c     | 6 +++---
 drivers/cpufreq/amd-pstate.c | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

-- 
2.34.1

[PATCH v2 1/5] ACPI: CPPC: Detect preferred core availability on online CPUs

[Gautham R. Shenoy]

Commit 279f838a61f9 ("x86/amd: Detect preferred cores in
amd_get_boost_ratio_numerator()") introduced the ability to detect the
preferred core on AMD platforms by checking if there at least two
distinct highest_perf values.

However, it uses for_each_present_cpu() to iterate through all the
CPUs in the platform, which is problematic when the kernel is booted
with "nosmt=force" commandline option.

Hence limit the search to only the online CPUs.

Fixes: 279f838a61f9 ("x86/amd: Detect preferred cores in amd_get_boost_ratio_numerator()")
Reported-by: Christopher Harris <chris.harris79@gmail.com>
Closes: https://lore.kernel.org/lkml/CAM+eXpdDT7KjLV0AxEwOLkSJ2QtrsvGvjA2cCHvt1d0k2_C4Cw@mail.gmail.com/
Reviewed-by: "Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>
Tested-by: Chrisopher Harris <chris.harris79@gmail.com>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 arch/x86/kernel/acpi/cppc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index 7047124490f6..d7c8ef1e354d 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -196,7 +196,7 @@ int amd_detect_prefcore(bool *detected)
 		break;
 	}
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		u32 tmp;
 		int ret;
 
-- 
2.34.1

[PATCH v2 2/5] ACPI: CPPC: Check _CPC validity for only the online CPUs

[Gautham R. Shenoy]

per_cpu(cpc_desc_ptr, cpu) object is initialized for only the online
CPUs via acpi_soft_cpu_online() --> __acpi_processor_start() -->
acpi_cppc_processor_probe().

However the function acpi_cpc_valid() checks for the validity of the
_CPC object for all the present CPUs. This breaks when the kernel is
booted with "nosmt=force".

Hence check the validity of the _CPC objects of only the online CPUs.

Fixes: 2aeca6bd0277 ("ACPI: CPPC: Check present CPUs for determining _CPC is valid")
Reported-by: Christopher Harris <chris.harris79@gmail.com>
Closes: https://lore.kernel.org/lkml/CAM+eXpdDT7KjLV0AxEwOLkSJ2QtrsvGvjA2cCHvt1d0k2_C4Cw@mail.gmail.com/
Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: "Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>
Tested-by: Chrisopher Harris <chris.harris79@gmail.com>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 drivers/acpi/cppc_acpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index ab4651205e8a..50e6348b511f 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -460,7 +460,7 @@ bool acpi_cpc_valid(void)
 	if (acpi_disabled)
 		return false;
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		cpc_ptr = per_cpu(cpc_desc_ptr, cpu);
 		if (!cpc_ptr)
 			return false;
-- 
2.34.1

[PATCH v2 3/5] ACPI: CPPC: Perform fast check switch only for online CPUs

[Gautham R. Shenoy]

per_cpu(cpc_desc_ptr, cpu) object is initialized for only the online
CPUs via acpi_soft_cpu_online() --> __acpi_processor_start() -->
acpi_cppc_processor_probe().

However the function cppc_allow_fast_switch() checks for the validity
of the _CPC object for all the present CPUs. This breaks when the
kernel is booted with "nosmt=force".

Check fast_switch capability only on online CPUs

Fixes: 15eece6c5b05 ("ACPI: CPPC: Fix NULL pointer dereference when nosmp is used")
Reviewed-by: "Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 drivers/acpi/cppc_acpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 50e6348b511f..fb7696b27d82 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -476,7 +476,7 @@ bool cppc_allow_fast_switch(void)
 	struct cpc_desc *cpc_ptr;
 	int cpu;
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		cpc_ptr = per_cpu(cpc_desc_ptr, cpu);
 		desired_reg = &cpc_ptr->cpc_regs[DESIRED_PERF];
 		if (!CPC_IN_SYSTEM_MEMORY(desired_reg) &&
-- 
2.34.1

[PATCH v2 4/5] ACPI: CPPC: Limit perf ctrs in PCC check only to online CPUs

[Gautham R. Shenoy]

per_cpu(cpc_desc_ptr, cpu) object is initialized for only the online
CPU via acpi_soft_cpu_online() --> __acpi_processor_start() -->
acpi_cppc_processor_probe().

However the function cppc_perf_ctrs_in_pcc() checks if the CPPC
perf-ctrs are in a PCC region for all the present CPUs, which breaks
when the kernel is booted with "nosmt=force".

Hence, limit the check only to the online CPUs.

Fixes: ae2df912d1a5 ("ACPI: CPPC: Disable FIE if registers in PCC regions")
Reviewed-by: "Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 drivers/acpi/cppc_acpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index fb7696b27d82..f49c72d3a78b 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1435,7 +1435,7 @@ bool cppc_perf_ctrs_in_pcc(void)
 {
 	int cpu;
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		struct cpc_register_resource *ref_perf_reg;
 		struct cpc_desc *cpc_desc;
 
-- 
2.34.1

[PATCH v2 5/5] cpufreq/amd-pstate: Call cppc_set_auto_sel() only for online CPUs

[Gautham R. Shenoy]

amd_pstate_change_mode_without_dvr_change() calls cppc_set_auto_sel()
for all the present CPUs.

However, this callpath eventually calls cppc_set_reg_val() which
accesses the per-cpu cpc_desc_ptr object. This object is initialized
only for online CPUs via acpi_soft_cpu_online() -->
__acpi_processor_start() --> acpi_cppc_processor_probe().

Hence, restrict calling cppc_set_auto_sel() to only the online CPUs.

Fixes: 3ca7bc818d8c ("cpufreq: amd-pstate: Add guided mode control support via sysfs")
Suggested-by: "Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 drivers/cpufreq/amd-pstate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index b44f0f7a5ba1..602e4fa81d6c 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1282,7 +1282,7 @@ static int amd_pstate_change_mode_without_dvr_change(int mode)
 	if (cpu_feature_enabled(X86_FEATURE_CPPC) || cppc_state == AMD_PSTATE_ACTIVE)
 		return 0;
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		cppc_set_auto_sel(cpu, (cppc_state == AMD_PSTATE_PASSIVE) ? 0 : 1);
 	}
 
-- 
2.34.1

Re: [PATCH v2 0/5] CPPC/amd-pstate: Fixes to limit actions to online CPUs

[Rafael J. Wysocki]

Hi,

On Fri, Nov 7, 2025 at 8:42 AM Gautham R. Shenoy <gautham.shenoy@amd.com> wrote:
>
> Hello,
>
> This is the v2 of the patchset to restrict certain actions to only
> online CPUs instead of present CPUs.
>
> The v1 of this patchset can be found here:
> https://lore.kernel.org/lkml/20251105143851.4251-1-gautham.shenoy@amd.com/
>
> Changes between v1 --> v2:
>
>  * Picked up the Reviewed-by tags from Mario for the first four
>    patches
>
>  * Picked up the Tested-by tags from Chris for the first two patches
>
>  * Added a fifth patch to fix calling of cppc_set_auto_sel() for only
>    online CPUs in the amd-pstate driver code (Mario)
>
>
> Gautham R. Shenoy (5):
>   ACPI: CPPC: Detect preferred core availability on online CPUs
>   ACPI: CPPC: Check _CPC validity for only the online CPUs
>   ACPI: CPPC: Perform fast check switch only for online CPUs
>   ACPI: CPPC: Limit perf ctrs in PCC check only to online CPUs

The above 4 patches applied as 6.18-rc material.

>   cpufreq/amd-pstate: Call cppc_set_auto_sel() only for online CPUs

And I'm leaving this one to Mario.

Thanks!

Re: [PATCH v2 0/5] CPPC/amd-pstate: Fixes to limit actions to online CPUs

[Chris Harris]

Hi, I've tested all five v2 patches and have observed no issues in the
use case the bug report was based upon.  I continue to successfully
receive the desired amd-pstate scaling driver when 'nosmt=force' and
'amd_pstate=passive' are set.  I've not tested other cases/scenarios
for which the additional hardening/patches may have been intended.

Thank you again for the rapid efforts that went into this solution.

Chris Harris

On Fri, Nov 7, 2025 at 9:41 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> Hi,
>
> On Fri, Nov 7, 2025 at 8:42 AM Gautham R. Shenoy <gautham.shenoy@amd.com> wrote:
> >
> > Hello,
> >
> > This is the v2 of the patchset to restrict certain actions to only
> > online CPUs instead of present CPUs.
> >
> > The v1 of this patchset can be found here:
> > https://lore.kernel.org/lkml/20251105143851.4251-1-gautham.shenoy@amd.com/
> >
> > Changes between v1 --> v2:
> >
> >  * Picked up the Reviewed-by tags from Mario for the first four
> >    patches
> >
> >  * Picked up the Tested-by tags from Chris for the first two patches
> >
> >  * Added a fifth patch to fix calling of cppc_set_auto_sel() for only
> >    online CPUs in the amd-pstate driver code (Mario)
> >
> >
> > Gautham R. Shenoy (5):
> >   ACPI: CPPC: Detect preferred core availability on online CPUs
> >   ACPI: CPPC: Check _CPC validity for only the online CPUs
> >   ACPI: CPPC: Perform fast check switch only for online CPUs
> >   ACPI: CPPC: Limit perf ctrs in PCC check only to online CPUs
>
> The above 4 patches applied as 6.18-rc material.
>
> >   cpufreq/amd-pstate: Call cppc_set_auto_sel() only for online CPUs
>
> And I'm leaving this one to Mario.
>
> Thanks!