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[PATCH] cpufreq: intel_pstate: Check IDA feature only during MSR 0x199 write

Srinivas Pandruvada posted 1 patch 2 months, 4 weeks ago 
drivers/cpufreq/intel_pstate.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
[PATCH] cpufreq: intel_pstate: Check IDA feature only during MSR 0x199 write
Posted by Srinivas Pandruvada 2 months, 4 weeks ago 
Commit ac4e04d9e378 ("cpufreq: intel_pstate: Unchecked MSR aceess in
legacy mode") introduced a check for feature X86_FEATURE_IDA to verify
turbo mode support. Although this is the correct way to check for turbo
mode, it causes issues on some platforms that disable turbo during OS
boot but enable it later. Without this feature check, users were able to
write 0 to /sys/devices/system/cpu/intel_pstate/no_turbo post-boot to
get turbo mode frequencies.

To restore the old behavior while still addressing the unchecked MSR
issue on some Skylake-X systems, limit the X86_FEATURE_IDA check to only
when setting MSR 0x199 Turbo Engage Bit (bit 32).

Fixes: ac4e04d9e378 ("cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode")
Reported-by: Aaron Rainbolt <arainbolt@kfocus.org>
Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2122531
Tested-by: Aaron Rainbolt <arainbolt@kfocus.org>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 drivers/cpufreq/intel_pstate.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 38897bb14a2c..492a10f1bdbf 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -603,9 +603,6 @@ static bool turbo_is_disabled(void)
 {
 	u64 misc_en;
 
-	if (!cpu_feature_enabled(X86_FEATURE_IDA))
-		return true;
-
 	rdmsrq(MSR_IA32_MISC_ENABLE, misc_en);
 
 	return !!(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE);
@@ -2106,7 +2103,8 @@ static u64 atom_get_val(struct cpudata *cpudata, int pstate)
 	u32 vid;
 
 	val = (u64)pstate << 8;
-	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
+	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) &&
+	    cpu_feature_enabled(X86_FEATURE_IDA))
 		val |= (u64)1 << 32;
 
 	vid_fp = cpudata->vid.min + mul_fp(
@@ -2271,7 +2269,8 @@ static u64 core_get_val(struct cpudata *cpudata, int pstate)
 	u64 val;
 
 	val = (u64)pstate << 8;
-	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
+	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) &&
+	    cpu_feature_enabled(X86_FEATURE_IDA))
 		val |= (u64)1 << 32;
 
 	return val;
-- 
2.51.0
Re: [PATCH] cpufreq: intel_pstate: Check IDA feature only during MSR 0x199 write
Posted by Rafael J. Wysocki 2 months, 3 weeks ago 
On Tue, Nov 11, 2025 at 2:09 AM Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
>
> Commit ac4e04d9e378 ("cpufreq: intel_pstate: Unchecked MSR aceess in
> legacy mode") introduced a check for feature X86_FEATURE_IDA to verify
> turbo mode support. Although this is the correct way to check for turbo
> mode, it causes issues on some platforms that disable turbo during OS
> boot but enable it later. Without this feature check, users were able to
> write 0 to /sys/devices/system/cpu/intel_pstate/no_turbo post-boot to
> get turbo mode frequencies.
>
> To restore the old behavior while still addressing the unchecked MSR
> issue on some Skylake-X systems, limit the X86_FEATURE_IDA check to only
> when setting MSR 0x199 Turbo Engage Bit (bit 32).
>
> Fixes: ac4e04d9e378 ("cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode")
> Reported-by: Aaron Rainbolt <arainbolt@kfocus.org>
> Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2122531
> Tested-by: Aaron Rainbolt <arainbolt@kfocus.org>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 38897bb14a2c..492a10f1bdbf 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -603,9 +603,6 @@ static bool turbo_is_disabled(void)
>  {
>         u64 misc_en;
>
> -       if (!cpu_feature_enabled(X86_FEATURE_IDA))
> -               return true;
> -
>         rdmsrq(MSR_IA32_MISC_ENABLE, misc_en);
>
>         return !!(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE);
> @@ -2106,7 +2103,8 @@ static u64 atom_get_val(struct cpudata *cpudata, int pstate)
>         u32 vid;
>
>         val = (u64)pstate << 8;
> -       if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
> +       if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) &&
> +           cpu_feature_enabled(X86_FEATURE_IDA))
>                 val |= (u64)1 << 32;
>
>         vid_fp = cpudata->vid.min + mul_fp(
> @@ -2271,7 +2269,8 @@ static u64 core_get_val(struct cpudata *cpudata, int pstate)
>         u64 val;
>
>         val = (u64)pstate << 8;
> -       if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
> +       if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) &&
> +           cpu_feature_enabled(X86_FEATURE_IDA))
>                 val |= (u64)1 << 32;
>
>         return val;
> --

Applied as 6.18-rc material, with some adjustments in the subject and changelog.

Thanks!

Patchew 2.1-devel-b67e4c2

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