From 7da9960b59fb7e590eb8538c9428db55a4ea2d23 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Thu, 24 Apr 2025 06:47:18 -0700 Subject: [PATCH] perf/x86/intel/ds: Fix counter backwards of non-precise events counters-snapshotting The counter backwards may be observed in the PMI handler when counters-snapshotting some non-precise events in the freq mode. For the non-precise events, it's possible the counters-snapshotting records a positive value for an overflowed PEBS event. Then the HW auto-reload mechanism reset the counter to 0 immediately. Because the pebs_event_reset is cleared in the freq mode, which doesn't set the PERF_X86_EVENT_AUTO_RELOAD. In the PMI handler, 0 will be read rather than the positive value recorded in the counters-snapshotting record. The counters-snapshotting case has to be specially handled. Since the event value has been updated when processing the counters-snapshotting record, only needs to set the new period for the counter via x86_pmu_set_period(). Fixes: e02e9b0374c3 ("perf/x86/intel: Support PEBS counters snapshotting") Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20250424134718.311934-6-kan.liang@linux.intel.com --- arch/x86/events/intel/ds.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 18c3ab579b8b..9b20acc0e932 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -2379,8 +2379,25 @@ __intel_pmu_pebs_last_event(struct perf_event *event, */ intel_pmu_save_and_restart_reload(event, count); } - } else - intel_pmu_save_and_restart(event); + } else { + /* + * For a non-precise event, it's possible the + * counters-snapshotting records a positive value for the + * overflowed event. Then the HW auto-reload mechanism + * reset the counter to 0 immediately, because the + * pebs_event_reset is cleared if the PERF_X86_EVENT_AUTO_RELOAD + * is not set. The counter backwards may be observed in a + * PMI handler. + * + * Since the event value has been updated when processing the + * counters-snapshotting record, only needs to set the new + * period for the counter. + */ + if (is_pebs_counter_event_group(event)) + static_call(x86_pmu_set_period)(event); + else + intel_pmu_save_and_restart(event); + } } static __always_inline void -- 2.25.1