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From: Wanpeng Li <kernellwp@gmail.com>
To: mjt@tls.msk.ru
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>,
	kvm <kvm@vger.kernel.org>
Subject: Re: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting
Date: Wed, 7 Apr 2021 19:01:42 +0800	[thread overview]
Message-ID: <CANRm+CySNYUZ_8eq_6SRiUB4q4W0QU8EkW1RAM+jtMZ26-PUEw@mail.gmail.com> (raw)
In-Reply-To: <36088364-0b3d-d492-0aa4-59ea8f1d1632@msgid.tls.msk.ru>

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.

Thanks for the report. I have a patch here which can fix it.


  parent reply	other threads:[~2021-04-07 11:02 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-06 20:17 Michael Tokarev
2021-04-06 21:47 ` Sean Christopherson
2021-04-08 13:18   ` Thomas Gleixner
2021-04-09  2:14     ` Wanpeng Li
2021-04-09  8:13     ` Wanpeng Li
2021-04-09  9:19       ` Thomas Gleixner
2021-04-07 11:01 ` Wanpeng Li [this message]
2021-04-13 10:48 ` Wanpeng Li

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