linux-kernel - Re: KCSAN + KVM = host reset

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Message-ID: <CANpmjNNUn9_Q30CSeqbU_TNvaYrMqwXkKCA23xO4ZLr2zO0w9Q@mail.gmail.com>
Date:   Thu, 9 Apr 2020 18:03:10 +0200
From:   Marco Elver <elver@...gle.com>
To:     Qian Cai <cai@....pw>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        "paul E. McKenney" <paulmck@...nel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: KCSAN + KVM = host reset

On Thu, 9 Apr 2020 at 17:30, Qian Cai <cai@....pw> wrote:
>
>
>
> > On Apr 9, 2020, at 11:22 AM, Marco Elver <elver@...gle.com> wrote:
> >
> > On Thu, 9 Apr 2020 at 17:10, Qian Cai <cai@....pw> wrote:
> >>
> >>
> >>
> >>> On Apr 9, 2020, at 3:03 AM, Marco Elver <elver@...gle.com> wrote:
> >>>
> >>> On Wed, 8 Apr 2020 at 23:29, Qian Cai <cai@....pw> wrote:
> >>>>
> >>>>
> >>>>
> >>>>> On Apr 8, 2020, at 5:25 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> >>>>>
> >>>>> On 08/04/20 22:59, Qian Cai wrote:
> >>>>>> Running a simple thing on this AMD host would trigger a reset right away.
> >>>>>> Unselect KCSAN kconfig makes everything work fine (the host would also
> >>>>>> reset If only "echo off > /sys/kernel/debug/kcsan” before running qemu-kvm).
> >>>>>
> >>>>> Is this a regression or something you've just started to play with?  (If
> >>>>> anything, the assembly language conversion of the AMD world switch that
> >>>>> is in linux-next could have reduced the likelihood of such a failure,
> >>>>> not increased it).
> >>>>
> >>>> I don’t remember I had tried this combination before, so don’t know if it is a
> >>>> regression or not.
> >>>
> >>> What happens with KASAN? My guess is that, since it also happens with
> >>> "off", something that should not be instrumented is being
> >>> instrumented.
> >>
> >> No, KASAN + KVM works fine.
> >>
> >>>
> >>> What happens if you put a 'KCSAN_SANITIZE := n' into
> >>> arch/x86/kvm/Makefile? Since it's hard for me to reproduce on this
> >>
> >> Yes, that works, but this below alone does not work,
> >>
> >> KCSAN_SANITIZE_kvm-amd.o := n
> >
> > There are some other files as well, that you could try until you hit
> > the right one.
> >
> > But since this is in arch, 'KCSAN_SANITIZE := n' wouldn't be too bad
> > for now. If you can't narrow it down further, do you want to send a
> > patch?
>
> No, that would be pretty bad because it will disable KCSAN for Intel
> KVM as well which is working perfectly fine right now. It is only AMD
> is broken.

Interesting. Unfortunately I don't have access to an AMD machine right now.

Actually I think it should be:

  KCSAN_SANITIZE_svm.o := n
  KCSAN_SANITIZE_pmu_amd.o := n

If you want to disable KCSAN for kvm-amd.

Thanks,
-- Marco