[PATCH v2 3/3] powerpc/perf: Update prev_count of event to get accurate values

[Gautam Menghani <gautam@linux.ibm.com>]

When vpa_pmu_read() is called twice while a process is running on a cpu,
the "event->hw.prev_count" variable returns a stale value on the 2nd
read which results in a larger value getting added to event->count.

Fix this by updating the event->hw.prev_count every time vpa_pmu_read()
is called.

Fixes: 176cda0619b6 ("powerpc/perf: Add perf interface to expose vpa counters")
Cc: <stable@vger.kernel.org>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
---
v1 -> v2:
1. Add stable/fixes tags.

 arch/powerpc/perf/vpa-pmu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/perf/vpa-pmu.c b/arch/powerpc/perf/vpa-pmu.c
index e79d98447c74..efc39f71553b 100644
--- a/arch/powerpc/perf/vpa-pmu.c
+++ b/arch/powerpc/perf/vpa-pmu.c
@@ -156,6 +156,7 @@ static void vpa_pmu_read(struct perf_event *event)
 	final_data = new_data - prev_data;
 
 	local64_add(final_data, &event->count);
+	local64_set(&event->hw.prev_count, new_data);
 }
 
 static void vpa_pmu_del(struct perf_event *event, int flags)
-- 
2.54.0