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

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