some additional comments regarding the procedure:
Hardware requirements:
The number of pci-lanes is important. A CPU supporting only 16 lanes could limit the two gpu if there are aditional devices which require pci-lanes, i.e. certain M2-SSD.
Also not every motherboard is useful. My old machine gave the host gpu PCI x16 and the guest gpu PCI x4 which is not sufficient (both PCIe slots were build and sold as “x16”). There was nothing I could do to change things from BIOS or OS side.
It was mentioned already to use Yast2. I recommend it as well, since you can easily set up a network bridge with it (in contrast to Ubuntu). This is useful if you want to run more than one VM at the same time connected to the WWW.
Legacy Windows: WIn XP and Win 7
One of the reasons why I got interested in this - I wanted to run my old XP games in a VM.
The above procedure works for WIn >=8, since it is UEFI-based. However, for older Windows systems one needs to use Seabios instead of the OVMF. In addition, the gpu need to be switched to VGA-mode as outlined in
http://vfio.blogspot.de/2015/05/vfio-gpu-how-to-series-part-5-vga-mode.html
It describes the use of a small script, i.e. called qemu-kvm.vga which I had to place in /usr/bin/qemu-kvm.vga in order to get it to work in Leap 42.2
Apart from that I would heavily recommend to read the following sites inside out
http://vfio.blogspot.de/2015/05/vfio-gpu-how-to-series-part-4-our-first.html
http://vfio.blogspot.de/2015/05/vfio-gpu-how-to-series-part-3-host.html
It helps to understand the background and is pretty detailed at all steps. Although written for Fedora, I could easily adapt it to Leap 42 and Tumbleweed as well. Ubuntu as host system gave me a lot of headaches, but it worked also in the end. Fortunately apparmor in LEap did not cause any problems during the implementation.
On last thing: It works even with 3 gpu - provided you have enough pci-lanes (40 in my case). So I run a WIndows XP on one screen/gpu, while having Netflix running on Ubuntu on a second screen/gpu, all taken care of by the host Leap 42.2 on the 3rd gpu/screen. One can easily compartmentalize Office, Gaming, Media, etc
The hardware, which I run this on: E5-1650v3; ASUS X99-E WS; GTX750 as host card, GTX 960 (Windows and Linux) and AMD R5 230 (Linux only) as guest gpu.