Re: KCSAN + KVM = host reset

Qian Cai
2020-04-09T23:00:38Z

> On Apr 9, 2020, at 5:28 PM, Qian Cai <cai@lca.pw> wrote:
>
>
>
>> 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?

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