powerpc/perf: Never program book3s PMCs with values >= 0x80000000

[firefly-linux-kernel-4.4.55.git] / arch / powerpc / perf / core-book3s.c

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index bae697cd592510cb320eb091fb5a930000944a02..6b0641c3f03f097c4aef760c9aa5fa307d2bcd5b 100644 (file)
--- 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);
 }
 
 /*