Windows 8.1 - GPU Passthrough

I am trying to run Windows 8.1 as a guest using KVM. The problem I am having appears to be fairly common, blank screen when passing through the GPU to Windows 8.1. I mostly would like a sanity check to make sure this will even work or if I am missing something obvious.

Here is the setup I am using currently:

MotherBoard:MSI - 970 GAMING (MS-7693)

CPU:AMD FX-8350 Eight-Core

HVM: Enabled

IOMMU: Enabled

GPU:EVGA GTX 750 Ti

I have both SVM and IOMMU Mode enabled on my MB and the firmware has been updated for the bios.

Here is the current XML config for my Win8.1:

<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>Windows 8.1</name>
  <uuid>83d836a4-11f5-ffda-47ba-5fd92d7abd5e</uuid>
  <metadata>
    <vmtemplate name="Custom" icon="windows.png" os="windows"/>
  </metadata>
  <memory unit='KiB'>4194304</memory>
  <currentMemory unit='KiB'>4194304</currentMemory>
  <memoryBacking>
    <nosharepages/>
    <locked/>
  </memoryBacking>
  <vcpu placement='static'>4</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='0'/>
    <vcpupin vcpu='1' cpuset='1'/>
    <vcpupin vcpu='2' cpuset='2'/>
    <vcpupin vcpu='3' cpuset='3'/>
  </cputune>
  <os>
    <type arch='x86_64' machine='pc-i440fx-2.3'>hvm</type>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='4' threads='1'/>
  </cpu>
  <clock offset='localtime'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source file='/mnt/cache/VMs/vdisk1.img'/>
      <target dev='hdc' bus='virtio'/>
      <boot order='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/ISOs/Windows.iso'/>
      <target dev='hda' bus='ide'/>
      <readonly/>
      <boot order='2'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/ISOs/virtio-win.iso'/>
      <target dev='hdb' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
    <controller type='usb' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:47:81:c0'/>
      <source bridge='virbr0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/Windows 8.1.org.qemu.guest_agent.0'/>
      <target type='virtio' name='org.qemu.guest_agent.0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x06a3'/>
        <product id='0x0ccb'/>
      </source>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x045e'/>
        <product id='0x00f9'/>
      </source>
    </hostdev>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
  <qemu:commandline>
    <qemu:arg value='-device'/>
    <qemu:arg value='ioh3420,bus=pci.0,addr=1c.0,multifunction=on,port=2,chassis=1,id=root.1'/>
    <qemu:arg value='-device'/>
    <qemu:arg value='vfio-pci,host=01:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on'/>
    <qemu:arg value='-device'/>
    <qemu:arg value='vfio-pci,host=01:00.1,bus=root.1,addr=00.1'/>
  </qemu:commandline>
</domain>

I have tried the following:

Added the rom:

<qemu:arg value='vfio-pci,host=01:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on,romfile=/mnt/user/ISOs/EVGA.GTX750Ti.2048.140109.rom'/>

Added pci-stub to the syslinux.cfg:

 append pci-stub.ids=10de:1380,10de:0fbc initrd=/bzroot 

It appears to be using the right drivers for the card to pass through I believe:

01:00.0 VGA compatible controller [0300]: NVIDIA Corporation GM107 [GeForce GTX 750 Ti] [10de:1380] (rev a2) (prog-if 00 [VGA controller])
        Subsystem: eVga.com. Corp. Device [3842:3753]
        Flags: fast devsel, IRQ 33
        Memory at fd000000 (32-bit, non-prefetchable) [size=16M]
        Memory at c0000000 (64-bit, prefetchable) [size=256M]
        Memory at d0000000 (64-bit, prefetchable) [size=32M]
        I/O ports at e000 [size=128]
        Expansion ROM at fe000000 [disabled] [size=512K]
        Capabilities: [60] Power Management version 3
        Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [78] Express Legacy Endpoint, MSI 00
        Capabilities: [100] Virtual Channel
        Capabilities: [250] Latency Tolerance Reporting
        Capabilities: [258] #1e
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
        Capabilities: [900] #19
        Kernel driver in use: vfio-pci

01:00.1 Audio device [0403]: NVIDIA Corporation Device [10de:0fbc] (rev a1)
        Subsystem: eVga.com. Corp. Device [3842:3753]
        Flags: fast devsel, IRQ 34
        Memory at fe080000 (32-bit, non-prefetchable) [size=16K]
        Capabilities: [60] Power Management version 3
        Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [78] Express Endpoint, MSI 00
        Kernel driver in use: vfio-pci

Both Machine Types (i440fx-2.3 or Q35-2.3).

When I get time this week I was going to go through this all on the OVMF but thought I would check if there was something I was overlooking before spending the time doing that?

Having the same issue here. Pair of GTX 970 cards though. I can pass through the secondary GPU without issue, but passing the primary GPU leaves me with a blank screen. Tried multiple configs, even bought another different branded GTX 970 (same issue) and an AMD R5 220 (same issue).

I have an AMD R5 230 instead of a 220 and it doesn't blank out on the first slot (the one closest to the CPU). But, my GTX 750 has the same issue. I read somewhere in the forums that it's an issue with unRaid not wanting to give up the card as a primary video card and that there's a setting that you can put on the unRaid config file to make it ignore that GPU and make it available for VM use. Maybe someone remembers that thread and can post the link.