[vfio-users] regression from linux 4.0.4 to 4.2.0

[Janusz]

W dniu 20.09.2015 o 18:09, Kővágó Zoltán pisze:
> Hello,
>
> I've been using vfio-pci to passthrough a GPU to virtual machine since
> some time now, and it worked great.  But this weekend I've finally had
> enough time to update kernel, and things are completely broken with
> the new kernel...
>
> I've been using the ACS override patch (and a quick-and-dirty fix for
> multiple GOPs, but created a proper-ish patch yesterday, see
> http://article.gmane.org/gmane.linux.kernel.efi/6332 ), CSM disabled
> in UEFI and using OVMF virtual machines.  The motherboard is an ASRock
> Z87M Extreme4, with two PCI video cards (an NVidia GT640 (the primary
> card, used for linux), for which I almost had to beg at Gigabyte
> support to send an UEFI compatible VBIOS, and a GTX980 (secondary
> card, to passthrough)).  The integrated Intel GPU is diabled in UEFI
> settings. I'm not sure if it's supposed to work, but with 4.0.4
> kernels it worked like a charm.
>
> Now with 4.2.0, when I start qemu the monitor attached to the
> secondary card powers down, and then nothing happens, except qemu
> eating about 150% cpu. I've started bisecting the kernel, and found
> out that
>
> d69afbc6b1b5d0579f13d1a6339d952c4f60a9f4 KVM: MMU: fix decoding cache
> type from MTRR
>
> is the culprit.  When mtrr is diabled, the old code returns 0xFF while
> the new returns MTRR_TYPE_UNCACHABLE.  I have absolutely no idea what
> the hell is going on here, but changing that return statement back
> solves the problem, until
>
> b18d5431acc7a2fd22767925f3a6f597aa4bd29e KVM: x86: fix CR0.CD
> virtualization
>
> If I comment out the if kvm_read_cd0 part it will work..  until
> 4e241557fc1cb560bd9e77ca1b4a9352732a5427, which is a merge commit(!).
> I'm attaching a patch, it fixes the problem until
> f2ae45edbca7ba5324eef01719ede0151dc5cead for me.  But as I said
> earlier I have no freakin' idea what's going on here.
>
> I have recompiled OVMF from svn yesterday evening, and have a
> recent-ish qemu master (with some audio related patches).  Tell me if
> you need any more information.
>
> Thanks,
> Zoltan
See http://thread.gmane.org/gmane.linux.kernel/1952205/focus=1996025 and
thread [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR