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

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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: 59af95e028 ("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

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This commit is contained in:

Dapeng Mi 2026-06-16 12:46:48 +08:00 • committed by Peter Zijlstra

parent 8767b4d730

commit 3c4ec9b2a5

3 changed files with 6 additions and 5 deletions

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3

arch/x86/events/core.c

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6

arch/x86/events/intel/core.c

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2

arch/x86/events/perf_event.h

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