perf/x86/intel: Keep cap_user_rdpmc in sync with RDPMC user-disable state

After introducing the RDPMC user disable feature, user-space RDPMC may
return 0 instead of the actual event count. This creates an inconsistency
with cap_user_rdpmc, where cap_user_rdpmc is set, but user-space RDPMC
only returns 0.

To accurately represent the user-space RDPMC capability, update
cap_user_rdpmc (depending on PERF_EVENT_FLAG_USER_READ_CNT) according to
the RDPMC user disable state. If RDPMC user disable is enabled,
cap_user_rdpmc is updated to false eventually, allowing user-space
programs to fall back to the read() syscall to obtain the real event
count.

Because PERF_EVENT_FLAG_USER_READ_CNT is evaluated in
x86_pmu_event_init(), move intel_pmu_update_rdpmc_user_disable()
earlier into intel_pmu_hw_config(). This ensures that the user-disable
state is updated before updating PERF_EVENT_FLAG_USER_READ_CNT. Note that
since event->ctx is not yet assigned at this stage, use the
PERF_ATTACH_TASK flag to detect whether the event is task-attached.

While at it, fix the indentation of x86_pmu_has_rdpmc_user_disable()
to adhere to the kernel coding style.

Fixes: 59af95e028d4 ("perf/x86/intel: Add support for rdpmc user disable feature")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260616044654.3468742-3-dapeng1.mi@linux.intel.com

3 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d1af33d96d0a..af0b67ffb43d 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2539,7 +2539,8 @@ static int x86_pmu_event_init(struct perf_event *event)
 	}
 
 	if (READ_ONCE(x86_pmu.attr_rdpmc) &&
-	    !(event->hw.flags & PERF_X86_EVENT_LARGE_PEBS))
+	    !(event->hw.flags & PERF_X86_EVENT_LARGE_PEBS) &&
+	    !(event->hw.config & ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE))
 		event->hw.flags |= PERF_EVENT_FLAG_USER_READ_CNT;
 
 	return err;
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 465c414f145d..5116b15438a2 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3533,7 +3533,7 @@ static void intel_pmu_update_rdpmc_user_disable(struct perf_event *event)
 	 */
 	if (x86_pmu.attr_rdpmc == X86_USER_RDPMC_ALWAYS_ENABLE ||
 	    (x86_pmu.attr_rdpmc == X86_USER_RDPMC_CONDITIONAL_ENABLE &&
-	     event->ctx->task))
+	     (event->attach_state & PERF_ATTACH_TASK)))
 		event->hw.config &= ~ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE;
 	else
 		event->hw.config |= ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE;
@@ -3547,8 +3547,6 @@ static void intel_pmu_enable_event(struct perf_event *event)
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
 
-	intel_pmu_update_rdpmc_user_disable(event);
-
 	if (unlikely(event->attr.precise_ip))
 		static_call(x86_pmu_pebs_enable)(event);
 
@@ -5147,6 +5145,8 @@ static int intel_pmu_hw_config(struct perf_event *event)
 		leader->hw.flags |= PERF_X86_EVENT_ACR;
 	}
 
+	intel_pmu_update_rdpmc_user_disable(event);
+
 	if ((event->attr.type == PERF_TYPE_HARDWARE) ||
 	    (event->attr.type == PERF_TYPE_HW_CACHE))
 		return 0;
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 5902a297daa1..a8afea8d38f0 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1344,7 +1344,7 @@ static inline u64 x86_pmu_get_event_config(struct perf_event *event)
 static inline bool x86_pmu_has_rdpmc_user_disable(struct pmu *pmu)
 {
 	return !!(hybrid(pmu, config_mask) &
-		 ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE);
+		  ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE);
 }
 
 extern struct event_constraint emptyconstraint;