[vfio-users] Cannot fix Error 43 for GTX 680 passed through to win 10 guest

[root at yoshi.dynu.com]

Hi vifo-users,

i really hope you can help me with this task.

I run Arch linux as a host with two guest VMs on it.

My machine:
Intel Xeon X5650
Sapphire Pure Black X58
24 GB Ram DDR3
Nvidia GT 210 (host)
Nvidia GT 9600 (reserved for guest)
Nvidia GTX 680 (reserved for guest)

I use qemu 2.4.5 and linux-vfio-lts kernel 4.1.9-1

kernel flags:

intel_iommu=on vfio-pci.ids=10de:1180,10de:0622,8086:3a3e 
intel_iommu=verbose pcie_acs_override=downstream i915.enable_hd_vgaarb=1

i run the Win10-Vm like this:

sudo qemu-system-x86_64 -enable-kvm -M q35 -m 8192 -cpu host,kvm=off \
-smp 4,sockets=1,cores=2,threads=2 \
-boot d \
-drive file=Downloads/Win10_German_x64.iso,if=ide,index=1,media=cdrom \
-drive file=Downloads/virtio-win.iso,if=ide,index=2,media=cdrom \
-drive file=testII.img,if=virtio \
-device 
ioh3420,bus=pcie.0,addr=1c.0,multifunction=on,port=1,chassis=1,id=rootbus 
\
-device 
vfio-pci,host=05:00.0,bus=rootbus,addr=00.0,multifunction=on,x-vga=on \
-device vfio-pci,host=00:1b.0,bus=rootbus,addr=00.1 \
-usbdevice host:046d:c52b \
-usbdevice host:045e:0291 \
-vga none -vnc :5 -monitor stdio

where 05:00.0 is the GTX 680 and 00:1b.0 is my onboard ALC 892 sound 
card.

As soon as i install the nvidia drivers i get a code 43 for the card. I 
disabled the autoupdate of the drivers since windows installed 355.xx 
drivers over the installed 377.88 drivers (i read that there are 
problems with the newer ones).

What bugs me most is that it run correctly for a while (valley benchmark 
and even GTA 5 run flawlessly) and then broke again unfixable.

I also reinstalled windows (many times), tried different configurations, 
but nothing brought the GTX 680 back to life.

What i tried (and remember) so far:

q35/440fx machine -> code 43
adding the card directly to pcie.0-bus -> code 43
adding a emulated gpu as primary gpu -> no screen on connected monitor, 
code 43
flashed a uefi-compatible Bios on the card and tried OVMF -> no screen

Let me know if you need any more information.

I really hope you can help me to get it to work (again... this bothers 
me most of all.. that it worked and then broke out of nothing...)

Cheers