VGA Passthrough is one of the things you can do when you have more then one gpus. In my case I have one HD 7750 and GTX 770.

System config

Make sure your processor supports VT-d, motherboard supports IOMMU and also enable it. Note : I have seen few posts regarding some motherboards having lousy support for IOMMU.

Working settings for me

1. First thing to disable radeon drivers

2. Assigning it to pci_stub

3. Set flags for KVM

then execute

sudo update-initramfs

then reboot

4. Create script

    qemu-system-x86_64 -enable-kvm \
    -m 4096 \
    -hda win7.img -cdrom /path/to/iso \
    -cpu host
    -smp cores=8,threads=1,sockets=1 \
    -net nic -net tap \
    -vga cirrus \
    -device pci-assign,host=06:00.0 \
    -device pci-assign,host=06:00.1 \
    -soundhw hda

Video

Update : Benchmark

Bare metal - GTX 770

Bare metal - HD 7750

Novabench says GTX 770, but its HD 7750 (runnig on secondary).

VGA Passthrough - HD 7750 - Take 1

VGA Passthrough - HD 7750 - Take 2

Using

echo "options kvm-amd npt=0" > /etc/modprobe.d/kvm-amd.conf</code>

Refer : https://bbs.archlinux.org/viewtopic.php?pid=1270311#p1270311

VGA Passthrough - HD 7750 - Archlinux

Assigning GTX 770

I wasn’t able to assign GTX 770 as passthrough device, few notes about it.

• No reset option available under sysfs for device so even blacklisting nouveau and being used by pci_stub it was still giving output (blank) on screen.
• Couln’t find way to reset via setpci
• Haven’t tried on secondary pci slot, it should work on it. ( Update : Doesn’t work )

Update : Using VFIO in Archlinux

VGA Passthrough with VFIO works in Archlinux on my new upgraded motherboard Asus M5A99FX R2.0. Here are configurations for that.

System configuration

1. Add vfio modules to initial ramdisk

2. Run mkinitcpio -p linux

3. Add pci addresses to vfio options

4. Qemu command

qemu-system-x86_64 -m 4096 -enable-kvm \
-drive file=/path/to/disk/disk.img,format=raw \
-device vfio-pci,host=03:00.0 -device vfio-pci,host=03:00.1  -cpu host -smp cores=8,threads=1,sockets=1 \
-net nic -net bridge,br=bridge0 \
-vga cirrus \
-soundhw hda

References

• https://bbs.archlinux.org/viewtopic.php?id=162768
• https://wiki.debian.org/VGAPassthrough