Re: [PATCH v2 3/4] perf: arm_pmu: Add workaround for FUJITSU-MONAKA Erratum E#030002

[sashiko-bot@kernel.org]

> FUJITSU-MONAKA Erratum E#030002 affects FUJITSU-MONAKA CPU.
> 
> On affected FUJITSU-MONAKA CPUs, after a PMU event counter is
> stopped at a value just before overflow, an overflow might still
> be incorrectly detected, resulting interrupt storm in some case.
> 
> For example, if the following conditions are met:
>   1) Running perf to count an event in user space only
>   2) The event can also occur in kernel space
>   3) The counter value is set just before the overflow
>      (when using the -F option, initial counter value is -1)
> 
> when the kernel is about to return to user space after enabling
> the count, an overflow interrupt is incorrectly triggered by an
> event that occurred in kernel space. Since the counter value is
> not updated (correctly), the interrupt handler does nothing and
> returns with the same condition. This leads to another wrong interrupt
> and results in an interrupt storm and eventually a softlockup.
> 
> Work around the erratum by avoiding programming PMU event counters
> with values within five counts of overflow.
> 
> Signed-off-by: Tomohiro Misono <misono.tomohiro@fujitsu.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261016-monaka-fix-for-upstream-v2-0-fc7ede7f9f48@fujitsu.com?part=3