perf/x86/intel: Check PEBS status correctly

[ Upstream commit fc17db8 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/events/intel/ds.c

@@ -1912,7 +1912,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
 		 * 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;