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From:   Marco Elver <elver@google.com>
Date:   Thu, 9 Apr 2020 17:22:48 +0200
Message-ID: <CANpmjNMEgc=+bLU472jy37hYPYo5_c+Kbyti8-mubPsEGBrm3A@mail.gmail.com>
Subject: Re: KCSAN + KVM = host reset
To:     Qian Cai <cai@lca.pw>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        "paul E. McKenney" <paulmck@kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org
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On Thu, 9 Apr 2020 at 17:10, Qian Cai <cai@lca.pw> wrote:
>
>
>
> > On Apr 9, 2020, at 3:03 AM, Marco Elver <elver@google.com> wrote:
> >
> > On Wed, 8 Apr 2020 at 23:29, Qian Cai <cai@lca.pw> wrote:
> >>
> >>
> >>
> >>> On Apr 8, 2020, at 5:25 PM, Paolo Bonzini <pbonzini@redhat.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 al=
so
> >>>> reset If only "echo off > /sys/kernel/debug/kcsan=E2=80=9D before ru=
nning 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 th=
at
> >>> is in linux-next could have reduced the likelihood of such a failure,
> >>> not increased it).
> >>
> >> I don=E2=80=99t remember I had tried this combination before, so don=
=E2=80=99t 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 :=3D 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 :=3D 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 :=3D n' wouldn't be too bad
for now. If you can't narrow it down further, do you want to send a
patch?

Thanks,
-- Marco

> I have been able to reproduce this on a few AMD hosts.
>
> > exact system, I'd ask you to narrow it down by placing 'KCSAN_SANITIZE
> > :=3D n' into suspect subsystems' Makefiles. Once you get it to work wit=
h
> > that, we can refine the solution.
> >
> > Thanks,
> > -- Marco
>