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Subject: Re: KCSAN + KVM = host reset
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <B5F0F530-911E-4B75-886A-9D8C54FF49C8@lca.pw>
Date:   Thu, 9 Apr 2020 19:00:31 -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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To:     Marco Elver <elver@google.com>
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> On Apr 9, 2020, at 5:28 PM, Qian Cai <cai@lca.pw> wrote:
>=20
>=20
>=20
>> On Apr 9, 2020, at 12:03 PM, Marco Elver <elver@google.com> wrote:
>>=20
>> On Thu, 9 Apr 2020 at 17:30, Qian Cai <cai@lca.pw> wrote:
>>>=20
>>>=20
>>>=20
>>>> On Apr 9, 2020, at 11:22 AM, Marco Elver <elver@google.com> wrote:
>>>>=20
>>>> On Thu, 9 Apr 2020 at 17:10, Qian Cai <cai@lca.pw> wrote:
>>>>>=20
>>>>>=20
>>>>>=20
>>>>>> 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.
>>>>>=20
>>>>> No, KASAN + KVM works fine.
>>>>>=20
>>>>>>=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
>>>>>=20
>>>>> Yes, that works, but this below alone does not work,
>>>>>=20
>>>>> KCSAN_SANITIZE_kvm-amd.o :=3D n
>>>>=20
>>>> There are some other files as well, that you could try until you =
hit
>>>> the right one.
>>>>=20
>>>> 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?
>>>=20
>>> 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.
>>=20
>> Interesting. Unfortunately I don't have access to an AMD machine =
right now.
>>=20
>> Actually I think it should be:
>>=20
>> KCSAN_SANITIZE_svm.o :=3D n
>> KCSAN_SANITIZE_pmu_amd.o :=3D n
>>=20
>> If you want to disable KCSAN for kvm-amd.
>=20
> KCSAN_SANITIZE_svm.o :=3D n
>=20
> That alone works fine. I am wondering which functions there could =
trigger
> perhaps some kind of recursing with KCSAN?

Another data point is set CONFIG_KCSAN_INTERRUPT_WATCHER=3Dn alone
also fixed the issue. I saw quite a few interrupt related function in =
svm.c, so
some interrupt-related recursion going on?=