linux-kernel - [PATCH AUTOSEL 5.9 21/23] perf/x86/intel: Check PEBS status correctly

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Date:   Sat, 12 Dec 2020 11:08:02 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.9 21/23] perf/x86/intel: Check PEBS status correctly

From: Stephane Eranian <eranian@...gle.com>

[ Upstream commit fc17db8aa4c53cbd2d5469bb0521ea0f0a6dbb27 ]

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@...nel.org>
Signed-off-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20201126110922.317681-2-namhyung@kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/events/intel/ds.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 404315df1e167..cf12e5a956f7e 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1913,7 +1913,7 @@ 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;
-- 
2.27.0