Re: Vga passthrough to KVM Guest issues

Alex Williamson
2013-10-28T16:17:28Z

On Wed, 2013-10-16 at 21:08 +0200, Max Schettler wrote:
> Hi guys,
>
> Im trying to set up vga passthrough. I use the latest mainline kernel
> (3.12rc5) and patched qemu (1.6.50). When i try to start a VM using this
> command:
>
> qemu-system-x86_64 -enable-kvm -M q35 -m 1024 -cpu qemu64
> -bios /usr/share/qemu/bios.bin -vga none
> -device
> ioh3420,bus=pcie.0,addr=1c.0,multifunction=on,port=1,chassis=1,id=root.1
> -device vfio-pci,host=06:00.0,bus=root.1,multifunction=on,x-vga=on
> -device vfio-pci,host=06:00.1,bus=root.1
>
> The screen attached to the passthroughed GPU turns on but does not show
> any output.
> Also I get some warnings from amd_iommu and my kernel messages are full
> of AMD-Vi messages:
> "AMD-Vi: Completion-Wait loop timed out" and
> "AMD-Vi: Event logged [IOTLB_INV_TIMEOUT device=06:00.0
> address=0x0000000438544b90"
>
> If i dont stop the qemu process this eventually forces me to reboot
> since the host gets unusable.
>
> I uploaded the whole dmesg output, if its of any help here:
> http://pastebin.com/ki13dqEd
>
> My hardware is an AMD FX-8350 with an Gigabyte 970A-UD3 and a Gigabyte
> 7870OC.
>
> Any help is much appreciated, thanks in advance!

You seem to get the AMD-Vi errors even before using VFIO, so I'd suspect
there's something wrong with the setup from the beginning. Copying
Joerg in case he has any ideas. You can also try the
disable_hugepages=1 module option for vfio_iommu_type1 (can also be set
via sysfs), but I'm not sure it's related. Can you assign other devices
installed in the same slot? Thanks,

Alex