Re: KCSAN + KVM = host reset

Qian Cai
2020-04-09T15:10:32Z

> 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 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