Just as an update: I tried enabling my iGPU again and passing it through to the Windows VM.
I had hope since my last try was still under 24.04 and with a Linux VM.
I could actually isolate the GPU without problems and there also was no warning when I added it via “Edit” in the settings.
The VM started but did not recognize the GPU. When I searched for new devices in device manager it hung. After I waited a while and killed the VM (which took way longer than expected) the PCIe devices that were passed through were all shown as “Not available” and when I tried booting the VM again I only got an “Unknown PCI header type ‘127’” error message.
This also appeared after I removed all PCIe devices but the actual GPU from the VM.
There were all sorts of familiar error messages in syslog:
Jan 6 20:46:09 truenas1 kernel: vfio-pci 0000:0f:00.6: Unable to change power state from D3cold to D0, device inaccessible
Jan 6 20:46:09 truenas1 kernel: pcieport 0000:00:08.1: broken device, retraining non-functional downstream link at 2.5GT/s
Jan 6 20:46:09 truenas1 kernel: pcieport 0000:00:08.1: retraining failed
Jan 6 20:46:09 truenas1 kernel: pcieport 0000:00:08.1: broken device, retraining non-functional downstream link at 2.5GT/s
Jan 6 20:46:09 truenas1 kernel: pcieport 0000:00:08.1: retraining failed
Jan 6 20:46:09 truenas1 kernel: vfio-pci 0000:0f:00.0: not ready 1023ms after bus reset; waiting
Jan 6 20:46:09 truenas1 kernel: vfio-pci 0000:0f:00.0: not ready 2047ms after bus reset; waiting
I should also note that the machine is type q35 with TPM as it is Windows 11.
So all in all: still no luck with GPU acceleration even when trying to pass a whole GPU through.