--- arch/powerpc/kernel/perf_event.c

+++ arch/powerpc/kernel/perf_event.c

@@ -1220,6 +1220,28 @@ unsigned long perf_instruction_pointer(s

return ip;

}

+static bool pmc_overflow(unsigned long val)

+{

+ if ((int)val < 0)

+ return true;

+

+ /*

+ * Events on POWER7 can roll back if a speculative event doesn't

+ * eventually complete. Unfortunately in some rare cases they will

+ * raise a performance monitor exception. We need to catch this to

+ * ensure we reset the PMC. In all cases the PMC will be 256 or less

+ * cycles from overflow.

+ *

+ * We only do this if the first pass fails to find any overflowing

+ * PMCs because a user might set a period of less than 256 and we

+ * don't want to mistakenly reset them.

+ */

+ if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))

+ return true;

+

+ return false;

+}

+

/*

* Performance monitor interrupt stuff

*/

@@ -1267,7 +1289,7 @@ static void perf_event_interrupt(struct

if (is_limited_pmc(i + 1))

continue;

val = read_pmc(i + 1);

- if ((int)val < 0)

+ if (pmc_overflow(val))

write_pmc(i + 1, 0);

}

}