[vfio-users] UEFI Win7 VM randomly does not start

[Laszlo Ersek]

On 10/17/15 15:15, Alex Williamson wrote:
> On Sat, 2015-10-17 at 10:50 +0200, Alexander Petrenz wrote:
>> Hi all,
>>
>> I have the problem that my UEFI VM for a Windows 7 guest does not always
>> starts properly. When it doesn´t work I have to try it again and finally it
>> will work after something between 3 to 6 attempts. The only error message
>> is:
>> qemu-system-x86_64: Guest moved used index from 13 to 0
> 
> This is a virtio issue that ring indexes are out of sync.  If you can
> come up with a reproducible scenario on latest kernel and qemu, it
> should be reported to the qemu-devel mailing list.  I've seen it
> occasionally, but not consistently enough to debug.  Thanks,

Very interesting; just the other day I fixed a theoretical issue in OVMF
that could explain this -- although I had never experienced these
symptoms caused *directly* by OVMF.

The reproducer script <http://pastebin.com/yWubnz9Y> seems to use
virtio-blk with dataplane; that could be a contributing factor.

(1) I have seen the same error once with SeaBIOS:

  http://code.coreboot.org/p/seabios/source/commit/5f2d17d35b23

(2) I can tell from the qemu command line here that under OVMF, the
virtio-net NIC is bound by the iPXE oprom that is bundled with QEMU.
This is revelant because -- in addition to SeaBIOS (see above) -- I've
also seen the same from iPXE. It is fixed now in iPXE upstream, but I'm
unsure about the binaries bundled with QEMU.

  http://thread.gmane.org/gmane.network.ipxe.devel/3918

  http://git.ipxe.org/ipxe.git/commitdiff/755d2b8

(3) In any case, Gerd's most recent OVMF RPMs (built at git commit
368002a) contain the upstream fix for the problem, *if* (and that's a
large if!) it was indeed caused by OVMF itself:

  http://thread.gmane.org/gmane.comp.bios.edk2.devel/3156

  https://github.com/tianocore/edk2/commit/fbc80813eeb0
  https://github.com/tianocore/edk2/commit/fcb636ea4244

Alexander, if you can more-or-less consistently reproduce the issue,
would you mind retesting with the most recent build from Gerd? (Please
CC me on any replies.)

Thanks
Laszlo