Re: [v4.14.y] 3cce50dfec4a arm64: perf: Disable PMU while processing counter overflows

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Jun 16, 2021 at 01:09:49PM +0200, Aman Priyadarshi wrote:
> Hi Greg,
> 
> Following the conversation with Marc, we discovered that an
> important fix for ARM PMU is not backported to 4.14.y tree, it affects
> counter value and give out nonsensical result.
> 
> Can you please include the following commit?
> ```
> commit 3cce50dfec4a5b0414c974190940f47dd32c6dee
> Author: Suzuki K Poulose <suzuki.poulose@arm.com>
> Date:   Tue Jul 10 09:58:03 2018 +0100
> 
>     arm64: perf: Disable PMU while processing counter overflows
>     
>     The arm64 PMU updates the event counters and reprograms the
>     counters in the overflow IRQ handler without disabling the
>     PMU. This could potentially cause skews in for group counters,
>     where the overflowed counters may potentially loose some event
>     counts, while they are reprogrammed. To prevent this, disable
>     the PMU while we process the counter overflows and enable it
>     right back when we are done.
>     
>     This patch also moves the PMU stop/start routines to avoid a
>     forward declaration.
>     
>     Suggested-by: Mark Rutland <mark.rutland@arm.com>
>     Cc: Will Deacon <will.deacon@arm.com>
>     Acked-by: Mark Rutland <mark.rutland@arm.com>
>     Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>     Signed-off-by: Will Deacon <will.deacon@arm.com>
> ```

It does not apply cleanly so you will have to provide a working backport
for us.

> For more details:
> 
> https://lists.cs.columbia.edu/pipermail/kvmarm/2021-June/047471.html


lore.kernel.org is your friend :)

thanks,

greg k-h