You are on the correct track already. GPU Passthrough is not perfect, especially if it's an NVidia Card (Which you don't mention NVidia or AMD). Finish the setup on the Qemu Window. Make sure the Windows Machine is connected to Internet and let Windows Update install the graphics drivers for you. When you come back you should be greeted by a second monitor, if not, reboot. I usually then remove the spice/vnc console and only have the GPU monitor attached. Getting GPU Passthrough to work is all about trial and error.
Other things to try:
- Install Windows without GPU passthrough, then attempt to passthrough GPU.
- Install drivers via NVidia_drivers.exe
- Install drivers via Windows Update
- Bios vs UEFI
- Q35 vs i440fx
Note: Code 43 is a known error w/ NVidia relating to NVidia drivers checking if they are running in a VM. NVidia sells cards specifically for running in a VM environment and attempts to block installation of drivers for consumer grade cards in a VM. You need to make sure to use the following in your domain.xml
<kvm>
<hidden state='on'/>
</kvm>
See https://passthroughpo.st/apply-error-43-workaround/ and other resources for examples.
Here is a screenshot of my config:
Here is the "relevant" part of my domain.xml, I can share entire thing if you want, but it's got a bunch of unnecessary things.
<os>
<type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type>
<loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
<nvram>/var/lib/libvirt/qemu/nvram/Windows10_VARS.fd</nvram>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<kvm>
<hidden state='on'/>
</kvm>
<vmport state='off'/>
</features>
<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup'/>
<timer name='pit' tickpolicy='delay'/>
<timer name='hpet' present='no'/>
</clock>