[Patch v2 2/2] perf/x86: Update cap_user_rdpmc base on rdpmc user disable state

[Dapeng Mi]

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 based on the RDPMC user disable state. If RDPMC user
disable is enabled, cap_user_rdpmc is set to false, allowing user-space
programs to fall back to the read() syscall to obtain the real event
count.

Since arch_perf_update_userpage() could be called for software events,
enhance x86_pmu_has_rdpmc_user_disable() to only check the x86 PMUs.

Fixes: 59af95e028d4 ("perf/x86/intel: Add support for rdpmc user disable feature")
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 
v2: Add is_x86_pmu() check before checking if rdpmc user disable feature
is supported.

v1: https://lore.kernel.org/all/20260311075201.2951073-2-dapeng1.mi@xxxxxxxxxxxxxxx/

 arch/x86/events/core.c       | 3 +++
 arch/x86/events/perf_event.h | 5 +++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 66b1a873c395..34eda8813716 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2794,6 +2794,9 @@ void arch_perf_update_userpage(struct perf_event *event,
 	userpg->cap_user_time_zero = 0;
 	userpg->cap_user_rdpmc =
 		!!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
+	if (x86_pmu_has_rdpmc_user_disable(event->pmu) &&
+	    event->hw.config & ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE)
+		userpg->cap_user_rdpmc = 0;
 	userpg->pmc_width = x86_pmu.cntval_bits;
 
 	if (!using_native_sched_clock() || !sched_clock_stable())
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 025f67726ecc..307361b106d2 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1351,8 +1351,9 @@ 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);
+	return is_x86_pmu(pmu) &&
+	       (hybrid(pmu, config_mask) &
+		ARCH_PERFMON_EVENTSEL_RDPMC_USER_DISABLE);
 }
 
 extern struct event_constraint emptyconstraint;
-- 
2.34.1