Vga passthrough to KVM Guest issues

[Max Schettler <max.schettler@googlemail.com>]

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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!

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