Re: kvm splat in mmu_spte_clear_track_bits

From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Adam Borowski <kilobyte@angband.pl>
Cc: Wanpeng Li <kernellwp@gmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>, kvm <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: kvm splat in mmu_spte_clear_track_bits
Date: Mon, 21 Aug 2017 21:58:34 +0200	[thread overview]
Message-ID: <20170821195833.GA696@flask> (raw)
In-Reply-To: <20170821191203.jospdwqpnixlotx3@angband.pl>

2017-08-21 21:12+0200, Adam Borowski:
> On Mon, Aug 21, 2017 at 09:26:57AM +0800, Wanpeng Li wrote:
> > 2017-08-21 7:13 GMT+08:00 Adam Borowski <kilobyte@angband.pl>:
> > > Hi!
> > > I'm afraid I keep getting a quite reliable, but random, splat when running
> > > KVM:
> > 
> > I reported something similar before. https://lkml.org/lkml/2017/6/29/64
> 
> Your problem seems to require OOM; I don't have any memory pressure at all:
> running a single 2GB guest while there's nothing big on the host (bloatfox,
> xfce, xorg, terminals + some minor junk); 8GB + (untouched) swap.  There's
> no memory pressure inside the guest either -- none was Linux (I wanted to
> test something on hurd, kfreebsd) and I doubt they even got to use all of
> their frames.

I even tried hurd, but couldn't reproduce ... what is your qemu command
line and the output of host's `grep . /sys/module/kvm*/parameters/*`?

> 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`

Thanks.