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-rw-r--r--arch/powerpc/perf/core-book3s.c17
1 files changed, 16 insertions, 1 deletions
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index bae697cd5925..6b0641c3f03f 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -996,7 +996,22 @@ static void power_pmu_read(struct perf_event *event)
} while (local64_cmpxchg(&event->hw.prev_count, prev, val) != prev);
local64_add(delta, &event->count);
- local64_sub(delta, &event->hw.period_left);
+
+ /*
+ * A number of places program the PMC with (0x80000000 - period_left).
+ * We never want period_left to be less than 1 because we will program
+ * the PMC with a value >= 0x800000000 and an edge detected PMC will
+ * roll around to 0 before taking an exception. We have seen this
+ * on POWER8.
+ *
+ * To fix this, clamp the minimum value of period_left to 1.
+ */
+ do {
+ prev = local64_read(&event->hw.period_left);
+ val = prev - delta;
+ if (val < 1)
+ val = 1;
+ } while (local64_cmpxchg(&event->hw.period_left, prev, val) != prev);
}
/*