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

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Message-Id: <B7F7F73E-EE27-48F4-A5D0-EBB29292913E@lca.pw>
Date:   Thu, 9 Apr 2020 11:10:28 -0400
From:   Qian Cai <cai@....pw>
To:     Marco Elver <elver@...gle.com>
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 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

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
> := n' into suspect subsystems' Makefiles. Once you get it to work with
> that, we can refine the solution.
> 
> Thanks,
> -- Marco