GPU Passthrough: Fedora won't boot with Nvidia Card plugged in

I’m running Fedora 27 on a Vega 56 card with the plan to passthrough a 1080 to Windows for gaming. Then I get the problem in the title.

I’m working with some other issues involving Fedora and Vega, so I’m not to the GPU passthrough point yet, but Fedora always hangs after a few lines of bootup text whenever the 1080 is plugged in (despite the display being driven by the Vega). Removing the 1080 fixes the issue.

Please tell us a bit more about your system, which motherboard are you using? What is it showing on the output?

Since you are planning to not use the 1080 under linux anyway, i would try to disable its drivers for troubleshooting:

edit your grub config sudo nano /etc/default/grub and append the following to kernel cmdline:
rd.driver.blacklist=nouveau rd.driver.blacklist=nvidia
update your grub config sudo grub2-mkconfig -o /etc/grub2-efi.cfg

And create a file in the modprobe.d directory sudo nano /etc/modprobe.d/blacklist-nvidia.conf with following contents:

blacklist nouveau
blacklist nvidia

This is a nouveau issue. You need to blacklist nouveau to get the card working in software rendering mode using LLVM. Had the same problem installing from a fresh Fedora 26 with Nvidia cards. Your Host OS needs to start off without any kernel modules for display loaded. Afterwards, you can install the proprietary drivers no problem. Be sure to install Steam BEFORE you install your Nvidia drivers or Steam won’t install with the Nvidia drivers loaded on Fedora.

I fixed the issue a couple hours ago. The fix was more or less what you said, but I also did sudo dnf remove xorg-x11-drv-nouveau

Plugged the card back in and it ignores the card just fine.