GPU Passthrough on FM2+ AMD Computer

Hi,

I am trying to passthrough the GPU of the following computer:

CPU: Athlon x4 860k (no iGPU)

Motherboard: ASRock FM2A88M Extreme4+

Primary GPU for host: ATI Rage XL (in PCI slot)

GPU for passthrough: MSI GTX 750 Ti OC v1 (in PCIE 3.0 slot)

Guest OS: Windows 8.1 64 bit

syslinux.cfg:

default /syslinux/menu.c32
menu title Lime Technology
prompt 0
timeout 50
label KVM unRAID OS
menu default
kernel /bzimage
append amd_iommu=on vfio_iommu_type1.allow_unsafe_interrupts=1 pcie_acs_override=downstream initrd=/bzroot
label unRAID OS Safe Mode (no plugins)
kernel /bzimage
append initrd=/bzroot unraidsafemode
label Memtest86+
kernel /memtest
label Xen/unRAID OS
kernel /syslinux/mboot.c32
append /xen --- /bzimage --- /bzroot
label Xen/unRAID OS Safe Mode (no plugins)
kernel /syslinux/mboot.c32
append /xen --- /bzimage --- /bzroot unraidsafemode

XML:

<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>win8</name>
  <uuid>38be9180-8680-11e4-b116-123b93f75cba</uuid>
  <memory unit='KiB'>3906250</memory>
  <currentMemory unit='KiB'>3906250</currentMemory>
  <memoryBacking>
    <nosharepages/>
    <locked/>
  </memoryBacking>
  <vcpu placement='static'>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-q35-2.1'>hvm</type>
    <loader>/usr/share/qemu/bios-256k.bin</loader>
    <boot dev='cdrom'/>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic eoi='on'/>
    <kvm>
      <hidden state='on'/>
    </kvm>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='2' threads='1'/>
  </cpu>
  <clock offset='localtime'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='yes'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/disk/by-id/ata-WDC_WD10EALX-759BA1_WD-WCATR8239826'/>
      <target dev='sda' bus='sata'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdb' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <controller type='pci' index='0' model='pcie-root'/>
    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x0'/>
    </controller>
    <controller type='pci' index='2' model='pci-bridge'>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0'/>
    </controller>
    <controller type='sata' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
    </controller>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x2'/>
    </controller>
    <controller type='ide' index='0'/>
    <interface type='bridge'>
      <mac address='28:B8:83:97:FB:B7'/>
      <source bridge='br0'/>
      <model type='e1000'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
    </interface>
    <input type='tablet' bus='usb'/>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x046d'/>
        <product id='0xc246'/>
      </source>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x046d'/>
        <product id='0xc52e'/>
      </source>
    </hostdev>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x06' function='0x0'/>
    </memballoon>
  </devices>
  <qemu:commandline>
    <qemu:arg value='-device'/>
    <qemu:arg value='ioh3420,bus=pcie.0,addr=1c.0,multifunction=on,port=1,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>

Symptoms:

When I boot the guest the first time, I can see the bios screen and windows logo.  After booting into Windows, I installed Nvidia driver 334.89 and reboot the computer after installation finished.  Again, I can see the whole boot procedure on screen.  But when I go into Device Manager, the name "GTX 750 Ti" was shown correctly with a yellow exclamation mark and the GPU got a code 43 error.  Since there is display output from the GPU, I suspect it was working in VGA mode only.

If I passthrough the GPU as secondary graphics adapters, there is no display output from the GPU.  I can only VNC into host and see the same code 43 error for the GPU.

Would you please give me some advice?.  Thank you very much!