linux-kernel - Re: kvm splat in mmu_spte_clear_track

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Date:   Wed, 23 Aug 2017 14:22:46 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Adam Borowski <kilobyte@...band.pl>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Wanpeng Li <kernellwp@...il.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 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:
>>> On Mon, Aug 21, 2017 at 09:26:57AM +0800, Wanpeng Li wrote:
>>>> 2017-08-21 7:13 GMT+08:00 Adam Borowski <kilobyte@...band.pl>:
>>>>> 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 ...
> 
> Also happens with a win10 guest, and with multiple Linuxes.
> 
>> what is your qemu command
>> line and the output of host's `grep . /sys/module/kvm*/parameters/*`?
> 
> qemu-system-x86_64 -enable-kvm -m 2048 -vga qxl -usbdevice tablet \
>  -net bridge -net nic \
>  -drive file="$DISK",cache=writeback,index=0,media=disk,discard=on
> 
> qemu-system-x86_64 -enable-kvm -m 2048 -vga qxl -usbdevice tablet \
>  -net bridge -net nic \
>  -drive file="$DISK",cache=unsafe,index=0,media=disk,discard=on,if=virtio,format=raw
> 
> /sys/module/kvm/parameters/halt_poll_ns:200000
> /sys/module/kvm/parameters/halt_poll_ns_grow:2
> /sys/module/kvm/parameters/halt_poll_ns_shrink:0
> /sys/module/kvm/parameters/ignore_msrs:N
> /sys/module/kvm/parameters/kvmclock_periodic_sync:Y
> /sys/module/kvm/parameters/lapic_timer_advance_ns:0
> /sys/module/kvm/parameters/min_timer_period_us:500
> /sys/module/kvm/parameters/tsc_tolerance_ppm:250
> /sys/module/kvm/parameters/vector_hashing:Y
> /sys/module/kvm_amd/parameters/avic:0
> /sys/module/kvm_amd/parameters/nested:1
> /sys/module/kvm_amd/parameters/npt:1
> /sys/module/kvm_amd/parameters/vls:0
> 
>>> 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?  I
would also try commit 1372324b328cd5dabaef5e345e37ad48c63df2a9 to
identify whether it was caused by a KVM change in 4.13 or something else.

Paolo