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Subject[081/205] ARM: 6205/1: perf: ensure counter delta is treated as unsigned
2.6.34-stable review patch.  If anyone has any objections, please let us know.


From: Will Deacon <>

commit 446a5a8b1eb91a6990e5c8fe29f14e7a95b69132 upstream.

Hardware performance counters on ARM are 32-bits wide but atomic64_t
variables are used to represent counter data in the hw_perf_event structure.

The armpmu_event_update function right-shifts a signed 64-bit delta variable
and adds the result to the event count. This can lead to shifting in sign-bits
if the MSB of the 32-bit counter value is set. This results in perf output
such as:

Performance counter stats for 'sleep 20':

18446744073460670464 cycles <-- 0xFFFFFFFFF12A6000
7783773 instructions # 0.000 IPC
465 context-switches
161 page-faults
1172393 branches

20.154242147 seconds time elapsed

This patch ensures that the delta value is treated as unsigned so that the
right shift sets the upper bits to zero.

Acked-by: Jamie Iles <>
Signed-off-by: Will Deacon <>
Signed-off-by: Russell King <>
Signed-off-by: Greg Kroah-Hartman <>

arch/arm/kernel/perf_event.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -165,7 +165,7 @@ armpmu_event_update(struct perf_event *e
int shift = 64 - 32;
s64 prev_raw_count, new_raw_count;
- s64 delta;
+ u64 delta;

prev_raw_count = atomic64_read(&hwc->prev_count);

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