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

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Message-ID: <20260209234310.1440722-2-sathyanarayanan.kuppuswamy@linux.intel.com>
Date: Mon,  9 Feb 2026 15:43:09 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: "Rafael J . Wysocki" <rafael@...nel.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/2] powercap: intel_rapl: Remove incorrect CPU check in PMU context

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@...ux.intel.com>
Tested-by: Furquim Ulisses <ulisses.furquim@...el.com>
---
 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