Re: [PATCH] arm64: perf: Fix 64-bit event counter read truncation
From: Alexandru Elisei <hidden>
Date: 2021-03-10 10:54:10
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Hi Rob, On 3/10/21 12:44 AM, Rob Herring wrote:
Commit 0fdf1bb75953 ("arm64: perf: Avoid PMXEV* indirection") changed
armv8pmu_read_evcntr() to return a u32 instead of u64. The result is
silent truncation of the event counter when using 64-bit counters. Given
the offending commit appears to have passed thru several folks, it seems
likely this was a bad rebase after v8.5 PMU 64-bit counters landed.
Thank you for the fix, it does seem that I made a mistake when rebasing the
series. Version v4 of the PMU NMI series was sent in 2019, then patch 8673e02e5841
("arm64: perf: Add support for ARMv8.5-PMU 64-bit counters") from March 2020
changed the read of PMEVCNTR_EL0 to return an u64, then version v5 from June 2020
changed it back to returning an u32.
The result of read_pmvevcntr() is returned by armv8pmu_read_evcntr(), and it is an
unsigned long which is 64bits for arm64, so the patch looks good to me:
Reviewed-by: Alexandru Elisei <redacted>
Thanks,
Alex
quoted hunk ↗ jump to hunk
Fixes: 0fdf1bb75953 ("arm64: perf: Avoid PMXEV* indirection") Cc: Alexandru Elisei <redacted> Cc: Julien Thierry <redacted> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <redacted> Cc: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Rob Herring <robh@kernel.org> --- arch/arm64/kernel/perf_event.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c index 7d2318f80955..4658fcf88c2b 100644 --- a/arch/arm64/kernel/perf_event.c +++ b/arch/arm64/kernel/perf_event.c@@ -460,7 +460,7 @@ static inline int armv8pmu_counter_has_overflowed(u32 pmnc, int idx) return pmnc & BIT(ARMV8_IDX_TO_COUNTER(idx)); } -static inline u32 armv8pmu_read_evcntr(int idx) +static inline u64 armv8pmu_read_evcntr(int idx) { u32 counter = ARMV8_IDX_TO_COUNTER(idx);
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