Failed to start simple desktop display manager after trying gpu passthorugh

Hi, I just switched to manjaro kde plasma from windows. I love linux but I also love gaming and recently I have really been into forza horizon 4 and this cannot run using wine because its from the microsoft store. I decided I would follow muta from someordinarygamer's guide for gpu passthrough. Want to use linux for surfing the web and programming and windows vm for video editing and gaming. I followed muta's video to where he rebuilded the initframes or something and then I rebooted the computer. Nothing went to the display so I connected the display to the motherboard instead of the dGPU and switched the bios settings to use the iGPU and when I rebooted all it said was failed to start simple desktop display manager. I went to the console and typed startx which returned a bunch of data at the beginning and the said (EE) Fatal server error:
(EE) no screens found(EE) then please consult the X.Org Foundation support. I have some snapshots I could restore too from timeshift but I'd rather fix the error and use gpu passthrough. Or do I? I have some questions... If I succesfully passthrough my dedicated card to the vm then will I be able to use dual monitor on the host machine? Or only on the guest machine? While in the guest machine will I only be able to use one monitor? I could dual boot if I need to but I to learn more about gpu passthrough first. Thanks in advance for any help! Im running manjaro with linux 5.4.6 and was going to use the dGPU with the guest machine and the iGPU with the host maching (manjaro).

Hello :slightly_smiling_face:!
First of all, If you plan on using your iGPU instead of your dGPU you MUST somehow prevent the proprietary NVIDIA Driver AND nouveau from loading, or else your system will be unable to use your iGPU and get to a GUI. You can either blacklist the nvidia driver modules or uninstall the nvidia drivers. The problem is if they are loaded they lock your GPU and make it unable to be passed through, If you then pass through the GPU you won't be able to use it in qemu and it won't work on your system either.

You could E.g. create a driver blacklist:

sudo touch /etc/modprobe.d/99-disable-nvidia-gpu.conf

Then edit the file:

sudo nano /etc/modprobe.d/99-disable-nvidia-gpu.conf

Paste the following code into the file and save it (mouse wheel click for paste, ctrl+o for save):

blacklist nouveau
blacklist nvidia

Make sure to rebuild your init-RAM-filesystem (initramfs):

sudo mkinitcpio -P && sudo update-grub

After this no nvidia drivers should be loaded and your system might start working with the Intel iGPU.
Eventually you'll have to plug your screen into your Mainboard instead of the GPU when using linux, though ofter this isn't necessary.
If you want to re-enable nvidia drivers simply run:

sudo rm /etc/modprobe.d/99-disable-nvidia-gpu.conf

And your dGPU should run on Manjaro again.
I'd also recommend reading this guide: https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF

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