perf/x86/intel: Check PEBS status correctly

The kernel cannot disambiguate when 2+ PEBS counters overflow at the
same time. This is what the comment for this code suggests.  However,
I see the comparison is done with the unfiltered p->status which is a
copy of IA32_PERF_GLOBAL_STATUS at the time of the sample. This
register contains more than the PEBS counter overflow bits. It also
includes many other bits which could also be set.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201126110922.317681-2-namhyung@kernel.org

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 89dba58..485c506 100644 (file)
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1916,7 +1916,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
                 * that caused the PEBS record. It's called collision.
                 * If collision happened, the record will be dropped.
                 */
-               if (p->status != (1ULL << bit)) {
+               if (pebs_status != (1ULL << bit)) {
                        for_each_set_bit(i, (unsigned long *)&pebs_status, size)
                                error[i]++;
                        continue;