Re: KCSAN + KVM = host reset

Qian Cai
2020-04-09T21:28:53Z

> On Apr 9, 2020, at 12:03 PM, Marco Elver <elver@google.com> wrote:
>
> On Thu, 9 Apr 2020 at 17:30, Qian Cai <cai@lca.pw> wrote:
>>
>>
>>
>>> On Apr 9, 2020, at 11:22 AM, Marco Elver <elver@google.com> wrote:
>>>
>>> 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 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
>>>
>>> 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 := n' wouldn't be too bad
>>> for now. If you can't narrow it down further, do you want to send a
>>> patch?
>>
>> 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.
>
> Interesting. Unfortunately I don't have access to an AMD machine right now.
>
> Actually I think it should be:
>
> KCSAN_SANITIZE_svm.o := n
> KCSAN_SANITIZE_pmu_amd.o := n
>
> If you want to disable KCSAN for kvm-amd.

KCSAN_SANITIZE_svm.o := n

That alone works fine. I am wondering which functions there could trigger
perhaps some kind of recursing with KCSAN?