Re: [PATCH v1 1/2] powercap: intel_rapl: Remove incorrect CPU check in PMU context

[Raag Jadav <raag.jadav@intel.com>]

On Mon, Feb 09, 2026 at 03:43:09PM -0800, Kuppuswamy Sathyanarayanan wrote:
> The RAPL MSR read path incorrectly validates CPU context when called
> from the PMU subsystem:
> 
>     if (atomic) {
>         if (unlikely(smp_processor_id() != cpu))
>             return -EIO;
>         rdmsrq(ra->reg.msr, ra->value);
>     }
> 
> This check fails for package-scoped MSRs like RAPL energy counters,
> which are readable from any CPU within the package.
> 
> The perf tool avoids hitting this check by validating against
> /sys/bus/event_source/devices/power/cpumask before opening events.
> However, turbostat does not perform this validation and may attempt
> reads from non-lead CPUs, causing the check to fail and return zero
> power values.
> 
> Since package-scoped MSRs are architecturally accessible from any CPU
> in the package, remove the CPU matching check.
> 
> Also rename 'atomic' to 'pmu_ctx' to clarify this indicates PMU context
> where rdmsrq() can be used directly instead of rdmsrl_safe_on_cpu().
> 
> Fixes: 748d6ba43afd ("powercap: intel_rapl: Enable MSR-based RAPL PMU support")
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Tested-by: Furquim Ulisses <ulisses.furquim@intel.com>

This fixes a regression[1] in our test suite.
Looks like the patch is already applied, but feel free to add my

Tested-by: Raag Jadav <raag.jadav@intel.com>

[1] https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6935

> ---
>  drivers/powercap/intel_rapl_common.c |  6 +++---
>  drivers/powercap/intel_rapl_msr.c    | 12 +++++-------
>  include/linux/intel_rapl.h           |  2 +-
>  3 files changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c
> index 3ff6da3bf4e6..3705d0608a0f 100644
> --- a/drivers/powercap/intel_rapl_common.c
> +++ b/drivers/powercap/intel_rapl_common.c
> @@ -254,7 +254,7 @@ static void rapl_init_domains(struct rapl_package *rp);
>  static int rapl_read_data_raw(struct rapl_domain *rd,
>  			      enum rapl_primitives prim,
>  			      bool xlate, u64 *data,
> -			      bool atomic);
> +			      bool pmu_ctx);
>  static int rapl_write_data_raw(struct rapl_domain *rd,
>  			       enum rapl_primitives prim,
>  			       unsigned long long value);
> @@ -832,7 +832,7 @@ prim_fixups(struct rapl_domain *rd, enum rapl_primitives prim)
>   */
>  static int rapl_read_data_raw(struct rapl_domain *rd,
>  			      enum rapl_primitives prim, bool xlate, u64 *data,
> -			      bool atomic)
> +			      bool pmu_ctx)
>  {
>  	u64 value;
>  	enum rapl_primitives prim_fixed = prim_fixups(rd, prim);
> @@ -854,7 +854,7 @@ static int rapl_read_data_raw(struct rapl_domain *rd,
>  
>  	ra.mask = rpi->mask;
>  
> -	if (rd->rp->priv->read_raw(get_rid(rd->rp), &ra, atomic)) {
> +	if (rd->rp->priv->read_raw(get_rid(rd->rp), &ra, pmu_ctx)) {
>  		pr_debug("failed to read reg 0x%llx for %s:%s\n", ra.reg.val, rd->rp->name, rd->name);
>  		return -EIO;
>  	}
> diff --git a/drivers/powercap/intel_rapl_msr.c b/drivers/powercap/intel_rapl_msr.c
> index 9a7e150b3536..152893dca565 100644
> --- a/drivers/powercap/intel_rapl_msr.c
> +++ b/drivers/powercap/intel_rapl_msr.c
> @@ -110,16 +110,14 @@ static int rapl_cpu_down_prep(unsigned int cpu)
>  	return 0;
>  }
>  
> -static int rapl_msr_read_raw(int cpu, struct reg_action *ra, bool atomic)
> +static int rapl_msr_read_raw(int cpu, struct reg_action *ra, bool pmu_ctx)
>  {
>  	/*
> -	 * When called from atomic-context (eg PMU event handler)
> -	 * perform MSR read directly using rdmsrq().
> +	 * When called from PMU context, perform MSR read directly using
> +	 * rdmsrq() without IPI overhead. Package-scoped MSRs are readable
> +	 * from any CPU in the package.
>  	 */
> -	if (atomic) {
> -		if (unlikely(smp_processor_id() != cpu))
> -			return -EIO;
> -
> +	if (pmu_ctx) {
>  		rdmsrq(ra->reg.msr, ra->value);
>  		goto out;
>  	}
> diff --git a/include/linux/intel_rapl.h b/include/linux/intel_rapl.h
> index f479ef5b3341..fa1f328d6712 100644
> --- a/include/linux/intel_rapl.h
> +++ b/include/linux/intel_rapl.h
> @@ -152,7 +152,7 @@ struct rapl_if_priv {
>  	union rapl_reg reg_unit;
>  	union rapl_reg regs[RAPL_DOMAIN_MAX][RAPL_DOMAIN_REG_MAX];
>  	int limits[RAPL_DOMAIN_MAX];
> -	int (*read_raw)(int id, struct reg_action *ra, bool atomic);
> +	int (*read_raw)(int id, struct reg_action *ra, bool pmu_ctx);
>  	int (*write_raw)(int id, struct reg_action *ra);
>  	void *defaults;
>  	void *rpi;
> -- 
> 2.43.0
>