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);
 }
 
 /*