linux-kernel - Re: kvm splat in mmu_spte_clear_track

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Date:   Fri, 25 Aug 2017 15:14:21 +0200
From:   Adam Borowski <kilobyte@...band.pl>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: kvm splat in mmu_spte_clear_track_bits

On Thu, Aug 24, 2017 at 03:43:55PM +0800, Wanpeng Li wrote:
> 2017-08-23 20:22 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> > On 22/08/2017 00:32, Adam Borowski wrote:
> >> On Mon, Aug 21, 2017 at 09:58:34PM +0200, Radim Krčmář wrote:
> >>> 2017-08-21 21:12+0200, Adam Borowski:
> >>>> Also, it doesn't reproduce for me on 4.12.
> >>>
> >>> Great info ... the most suspicious between v4.12 and v4.13-rc5 is the
> >>> series with dcdca5fed5f6 ("x86: kvm: mmu: make spte mmio mask more
> >>> explicit"), does reverting it help?
> >>>
> >>> `git revert ce00053b1cfca312c22e2a6465451f1862561eab~1..995f00a619584e65e53eff372d9b73b121a7bad5`
> >>
> >> Alas, doesn't seem to help.
> >>
> >> I've first installed a Debian stretch guest, the host survived both the
> >> installation and subsequent fooling around.  But then I started a win10
> >> guest which splatted as soon as the initial screen.
> >
> > Can you check if disabling THP on the host also fixes it for you?

As in: ?
echo never >/sys/kernel/mm/transparent_hugepage/enabled
echo never >/sys/kernel/mm/transparent_hugepage/defrag
Still reproduces, with or without reverting
ce00053b1cfca312c22e2a6465451f1862561eab~1..995f00a619584e65e53eff372d9b73b121a7bad5

> > I would also try commit 1372324b328cd5dabaef5e345e37ad48c63df2a9 to
> > identify whether it was caused by a KVM change in 4.13 or something
> > else.

I've ran different guests for a couple of hours, no explosions.  Thus it
looks like updating Cornelia's email address isn't the cause.

Too bad, there's 15k commits between 1372324b and 7f680d7ec315.

> For the OOM testcase, the splat will disappear if disabling THP.


Meow!
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