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perf/x86/intel/ds: Fix counter backwards of non-precise events counters-snapshotting

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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: e02e9b0374 ("perf/x86/intel: Support PEBS counters snapshotting")
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250424134718.311934-6-kan.liang@linux.intel.com
This commit is contained in:
Kan Liang
2025-04-24 06:47:18 -07:00
committed by Peter Zijlstra
parent e9988ad7b1
commit 7da9960b59
1 changed files with 19 additions and 2 deletions
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21
arch/x86/events/intel/ds.c
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@@ -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