Re: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting

[Wanpeng Li]

On Wed, 7 Apr 2021 at 18:55, Michael Tokarev <mjt@tls.msk.ru> wrote:
>
> Hi!
>
> It looks like this commit:
>
> commit 87fa7f3e98a1310ef1ac1900e7ee7f9610a038bc
> Author: Thomas Gleixner <tglx@linutronix.de>
> Date:   Wed Jul 8 21:51:54 2020 +0200
>
>      x86/kvm: Move context tracking where it belongs
>
>      Context tracking for KVM happens way too early in the vcpu_run()
>      code. Anything after guest_enter_irqoff() and before guest_exit_irqoff()
>      cannot use RCU and should also be not instrumented.
>
>      The current way of doing this covers way too much code. Move it closer to
>      the actual vmenter/exit code.
>
> broke kvm guest cpu time accounting - after this commit, when running
> qemu-system-x86_64 -enable-kvm, the guest time (in /proc/stat and
> elsewhere) is always 0.
>
> I dunno why it happened, but it happened, and all kernels after 5.9
> are affected by this.
>
> This commit is found in a (painful) git bisect between kernel 5.8 and 5.10.

Hi Michael,

Please have a try.
https://lore.kernel.org/kvm/1618298169-3831-1-git-send-email-wanpengli@tencent.com/

    Wanpeng