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Subject: Re: KCSAN + KVM = host reset
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <CANpmjNMiHNVh3BVxZUqNo4jW3DPjoQPrn-KEmAJRtSYORuryEA@mail.gmail.com>
Date:   Thu, 9 Apr 2020 11:10:28 -0400
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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 <CANpmjNMiHNVh3BVxZUqNo4jW3DPjoQPrn-KEmAJRtSYORuryEA@mail.gmail.com>
To:     Marco Elver <elver@google.com>
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> On Apr 9, 2020, at 3:03 AM, Marco Elver <elver@google.com> wrote:
>=20
> On Wed, 8 Apr 2020 at 23:29, Qian Cai <cai@lca.pw> wrote:
>>=20
>>=20
>>=20
>>> On Apr 8, 2020, at 5:25 PM, Paolo Bonzini <pbonzini@redhat.com> =
wrote:
>>>=20
>>> 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=E2=80=9D before =
running qemu-kvm).
>>>=20
>>> 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).
>>=20
>> 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.
>=20
> 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.

>=20
> 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

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 =
with
> that, we can refine the solution.
>=20
> Thanks,
> -- Marco