Will Deacon 446a5a8b1e
ARM: 6205/1: perf: ensure counter delta is treated as unsigned ...
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.
Cc: <stable@kernel.org >
Acked-by: Jamie Iles <jamie.iles@picochip.com >
Signed-off-by: Will Deacon <will.deacon@arm.com >
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk >
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