Re: 4.13-rc7: WARNING at arch/x86/kvm/mmu.c:717 (and a crash thereafter)

[Richard Weinberger]

On Mon, Aug 28, 2017 at 3:15 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Mon, 28 Aug 2017 15:06:00 +0200,
> Adam Borowski wrote:
>>
>> On Mon, Aug 28, 2017 at 02:26:06PM +0200, Takashi Iwai wrote:
>> > I seem to get a kernel warning when running KVM on Dell desktop with
>> > IvyBridge like below.  As you can see, a bad page BUG is triggered
>> > after that, too.  The problem is not triggered always, but it happens
>> > occasionally.
>>
>> See the thread starting with 20170820231302.s732zclznrqxwr46@xxxxxxxxxx
>>
>> > I haven't seen this on 4.13-rc4 at all, and IIRC, it started happening
>> > since rc5.  So this might be a regression at rc5.  But, as it doesn't
>> > happen always, I can't be 100% sure about it, and it's quite difficult
>> > to bisect (the test case isn't reliable), unfortunately.
>>
>> Same here -- it sometimes takes a few hours of trying to reproduce, which
>> makes proving the negative greatly unpleasant.
>>
>> And all I've been able to tell so far is that the problem is between
>> 4.13-rc4 and 4.13-rc5, just like you say.
>
> Good to hear that we can chorus!
> So if it's really a regression between rc4 and rc5, I see no obvious
> changes in arch/x86, i.e. it's likely somewhere else.
>
> (snip)
>> The first WARN is always the above.  But the rest seems to be totally random
>> -- a nasty case of fandango on core whose results range from harmless
>> through crash to massive data loss (just guess what would happen if some
>> idiot picked balancing the disk as a test load -- no one would be that
>> stupid, right?  At least an incomplete idiot has checksums and backups).
>
> Yeah, the crash after the WARNING seems quite random.

I don't see that warning but running qemu-kvm crashed by laptop
(4.13-rc4) two times in a row and
some userspace applications such has firefox or bash crashed randomly.

pstore-efi is now enabled to capture the stacktrace.

-- 
Thanks,
//richard