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 <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

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 18c3ab579b8b3ed92dd345893fb897a1b33d9224..9b20acc0e932e20770e5925c7314f1ef88bc28b8 100644 (file)
--- 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