From 3cb3c2f6886f9489df13de8efe7a1e803a3f21ea Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 17 Dec 2025 12:08:01 +0100 Subject: [PATCH] perf: Clean up mediated vPMU accounting The mediated_pmu_account_event() and perf_create_mediated_pmu() functions implement the exclusion between '!exclude_guest' counters and mediated vPMUs. Their implementation is basically identical, except mirrored in what they count/check. Make sure the actual implementations reflect this similarity. Notably: - while perf_release_mediated_pmu() has an underflow check; mediated_pmu_unaccount_event() did not. - while perf_create_mediated_pmu() has an inc_not_zero() path; mediated_pmu_account_event() did not. Also, the inc_not_zero() path can be outsite of perf_mediated_pmu_mutex. The mutex must guard the 0->1 (of either nr_include_guest_events or nr_mediated_pmu_vms) transition, but once a counter is already non-zero, it can safely be incremented further. Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20251208115156.GE3707891@noisy.programming.kicks-ass.net --- kernel/events/core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index dd842a4ca7895..e6a4b1e34f848 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6344,8 +6344,10 @@ static int mediated_pmu_account_event(struct perf_event *event) if (!is_include_guest_event(event)) return 0; - guard(mutex)(&perf_mediated_pmu_mutex); + if (atomic_inc_not_zero(&nr_include_guest_events)) + return 0; + guard(mutex)(&perf_mediated_pmu_mutex); if (atomic_read(&nr_mediated_pmu_vms)) return -EOPNOTSUPP; @@ -6358,6 +6360,9 @@ static void mediated_pmu_unaccount_event(struct perf_event *event) if (!is_include_guest_event(event)) return; + if (WARN_ON_ONCE(!atomic_read(&nr_include_guest_events))) + return; + atomic_dec(&nr_include_guest_events); } @@ -6373,10 +6378,10 @@ static void mediated_pmu_unaccount_event(struct perf_event *event) */ int perf_create_mediated_pmu(void) { - guard(mutex)(&perf_mediated_pmu_mutex); if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) return 0; + guard(mutex)(&perf_mediated_pmu_mutex); if (atomic_read(&nr_include_guest_events)) return -EBUSY; -- 2.47.3