From: Richa Bharti richa.bharti@siemens.com

[ Upstream commit 4b747cc628d8f500d56cf1338280eacc66362ff3 ]

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 support, it causes issues on some platforms that disable turbo during OS boot, but enable it later [1]. Before adding this feature check, users were able to get turbo mode frequencies by writing 0 to /sys/devices/system/cpu/intel_pstate/no_turbo post-boot.

To restore the old behavior on the affected systems while still addressing the unchecked MSR issue on some Skylake-X systems, check X86_FEATURE_IDA only immediately before updates of MSR_IA32_PERF_CTL that may involve setting the 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 [1] Tested-by: Aaron Rainbolt arainbolt@kfocus.org Signed-off-by: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com [ rjw: Subject adjustment, changelog edits ] Link: https://patch.msgid.link/20251111010840.141490-1-srinivas.pandruvada@linux.i... Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com [ richa: Backport to 6.12.y with context adjustments ] Signed-off-by: Richa Bharti richa.bharti@siemens.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 d0f4f7c2ae4d..9d8cb44c26c7 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -600,9 +600,6 @@ static bool turbo_is_disabled(void) { u64 misc_en;

- if (!cpu_feature_enabled(X86_FEATURE_IDA)) - return true; - rdmsrl(MSR_IA32_MISC_ENABLE, misc_en);

return !!(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE); @@ -2018,7 +2015,8 @@ 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( @@ -2183,7 +2181,8 @@ 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;