[vfio-users] VGA Passthrough fails without NoSnoop patch

[Javier Celaya]

Hello list

I've been looking for it, but I cannot find a solution to this problem. I
have a working Windows 10 VM with UEFI boot, which I pass an AMD Radeon RX
480. It also worked with a NVIDIA GTX 550Ti I had before. The thing is, it
only works with a QEMU 2.2 patched with the NoSnoop fix. With any later
release of QEMU, or without the patch, the VM:
- Throws an Error 43 with the NVIDIA card.
- Goes black on boot and reboots some seconds later with the AMD card
The vfio FAQ says that patch is not needed with a later release of QEMU, so
I'm wondering what I'm doing wrong...

My hardware is an Intel i5 2500, ASUS motherboard with a Z68 chipset, 16GB
of RAM. Both graphics cards appear in their own iommu group with the HDMI
sound card.

My QEMU command line is:

src/qemu/build-2.2-NoSnoop/x86_64-softmmu/qemu-system-x86_64

        -nodefaults
-no-user-config

        -enable-kvm -m 8192


        -cpu
Opteron_G1,+cx16,+lahf_lm,kvm=off

        -M
q35

        -smp 4,sockets=1,cores=4,threads=1
        -realtime mlock=on -rtc base=localtime,driftfix=slew
        -drive
file="OVMF_CODE-pure-efi.fd",if=pflash,format=raw,unit=0,readonly=on
        -drive file="OVMF_VARS-pure-efi.fd",if=pflash,format=raw,unit=1
        -drive file="$HD",id=disk1,if=virtio,cache=none
        -netdev bridge,id=netuser,br=br0
        -device virtio-net-pci,netdev=netuser,id=net0,mac=52:54:00:72:75:9e
        -device ich9-intel-hda,id=sound0
        -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0
        -device
ioh3420,bus=pcie.0,multifunction=on,port=1,chassis=1,id=root.0
        -usbdevice $JOYPAD
        -usbdevice $KEYBOARD
        -usbdevice $MOUSE
        -mem-path
$MEM_PATH
        -nographic -vga none
        -device
vfio-pci,host=01:00.0,id=hostdev0,bus=root.0,multifunction=on,x-vga=on
        -device vfio-pci,host=01:00.1,id=hostdev1,bus=pcie.0

I have tried, with the same results:
- Using the pc-i440fx machine
- Connecting the HDMI sound card to another bus
- Not connecting the HDMI sound card at all
- Using -cpu host (Windows 10 hangs with this configuration)
- Using -cpu core2duo

Any other idea?
Thank you

Javi
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