I need a video output from my server to be controlled by a Windows VM for a dedicated display.

I first started by attempting to pass-through the embedded VGA in this T440 server to the Windows VM. That turned out to be unstable, and would crash Unraid when starting or stopping the VM.

I have only a PCIe-1X slot, so I'm limited on choices to add a physical display card. I found an NVidia NVS300 which fit mechanically. I worked for weeks trying to get it to work, but eventually gave up. Apparently Nvidia blocks virtualization of that card for some reason so the driver will never load.

Now I have a Matrox G550 with a PCIe-1X interface. Again, it turns out to be quite a challenge. I've been working for days trying to get it work. The passthrough is working. It is seen by Windows as a Basic Display Adapter.

I can't install the drivers from the Matrox installer (with control panel) because the Matrox installer says there is no Matrox hardware present.

I can install the drivers by extracting the installer archive, and using the Device Manger Update Driver to point to the extracted drivers.

They install and seem to be working, but the display compresses the screen into the upper half of the display. The lower half is blank.

Gemini says this is due to improper initialization, and sent me on a long path of attempted fixes.

The card is initialized and displays the Unraid boot logo (mirrored to what is seen on the QXL video with VNC. The spinning white circle appears only on the QXL VNC display. The Unraid logo remains on the Matrox display, and a desktop is never shown. In Windows, Display Settings shows an 800x600 secondary display is present, but it is not driving the monitor on the Matrox, which only shows the Unraid boot logo.

With guidance from Gemini, I've adjusted the XML for the Matrox like this:

<hostdev mode='subsystem' type='pci' managed='yes'>

  <driver name='vfio'/>

  <source>

    <address domain='0x0000' bus='0x18' slot='0x00' function='0x0'/>

  </source>

  <alias name='hostdev1'/>

  <rom file='/mnt/user/isos/vbios/matrox_g550.rom'/>

  <property name='x-vga' value='off'/> 

  <address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0' boot='off'/></hostdev>

</hostdev>

That doesn't help.

Skipping a lot of mucking with the VGA BIOS and other suggestions, the latest suggestion was this:

1. Stop the VM.

2. SSH into your Unraid host and modify the vfio-pci module options. Use the G550's specific Device ID (2527) to avoid affecting the onboard G200eW (0536):
   Bash
   nano /etc/modprobe.d/vfio.conf
   # Add this line:
   options vfio-pci ids=102b:2527 disable_vga=1

After rebooting Unraid, that setting did not take effect.

root@T440:~# cat /sys/module/vfio_pci/parameters/disable_vga

N

root@T440:~#

Believing "Unraid doesn't use the standard update-initramfs -u command" , Gemini recommended the following to apply the new configuration:

modprobe -r vfio_pci

modprobe vfio_pci

That resulted in :

modprobe: FATAL: Module vfio_pci is builtin.

Now it's telling me to make changes to /boot/syslinux/syslinux.cfg.

This is typical for AI to go down rabbit holes when there might have been a wrong turn a while back. It seems that Gemini can be helpful with Windows, but it has very limited understanding of Unraid, so I'm hesitant to getting into boot configurations and such.

I've attached the entire saga with Gemini if anyone is interested. Matrox G550 - PCI passthrough in a KVM.docx

Before proceeding any further, I wanted to check here with knowledgeable humans to see if any of this makes sense or if there are other suggestions.

---

PS @PUNGGOKERS suggested Claude as better than Gemini, but Claude told me "Unfortunately, Claude is not available to new users right now. We’re working hard to expand our availability soon."

Edited October 26, 2025Oct 26 by timg11

Update after I thought more about this issue for a couple of days....

I told Gemini that 1) The Matrox installer did not recognize the card and refused to run; and 2) when I manually installed extracted drivers from Device Manager Update Driver, it sort of worked but the image was compressed in the upper half of the display.

Gemini thought those symptoms meant the QEMU was not properly initializing the Matrox, and went off on a rabbit trail of VBIOS, and various other attempts, finally leading to suggesting kernel changes for Unraid. At that point I realized it was off track and stopped.

I thought I'd go back to the manually installed drivers and do some testing with different DisplayPort to HDMI adapters on the two DIsplayPort outputs of the G550.

I re-installed the drivers, and the G550 was recognized and looked normal in Device Manager. Still had the 1/2 display on the HDMI monitor. The only other monitor I had in reach was a VGA analog. I had an adapter, so I plugged it in to the other port. Perfect video. I moved it to the first port. Perfect video. Then I borrowed another HDMI monitor and plugged it in the adapter and port I'd been testing with. Perfect video. So the 1/2 screen issue was a compatibility issue with a specific monitor.

So that HDMI incompatibility is still a mystery, but the Matrox card pass through into the Windows VM is solved.

Hi Thank you for your post.

I had G550 Pcie x1 also but having issue with gpu passthrough.

Although I'm on proxmox but I believe the procedure will be very similar.

I had it detected in my vm (windows 98, windows xp...), I was able to install driver using manual driver update however upon boot up i got all black screen.

Just couple of questions. Are you using seabios or ovmf , you mention windows 11, perhaps you used ovfm?

Is it possible you can share your g550 bios rom file?

Thank you.

This is the model I have:

@snsn that looks like the card I have.

I have attached the vbios ROM file I'm using.

The VM settings have OVMF TPM for BIOS.

matrox_g550.rom

@timg11 : thank you, I will test again with your bios. I'm just very surprised that this LEGACY card can work with OVMF. I keep thinking OVMF only work with gpu with bios supporting UEFI.

Edited November 25, 2025Nov 25 by snsn