VM with GPU passthrough - disabling default framebuffer?

woopla

So after fixing Ryzen Gen1 IOMMU issues (see here), I can pass my GPU to a VM. Problem is, the default framebuffer is still present and is the default graphics (for Linux or Windows).

My googling shows me there's a gfx_passthru option in Xen that tells Xen to disable the default framebuffer and use the passed-through GPU as the only VGA for the VM. Is there a way to do the same in XCP-NG?

Thanks,

Clement

olivierlambert

I have no experience with that. What's your GPU?

woopla

It's an Nvidia 1070

olivierlambert

With an Nvidia consumer grade GPU, passthrough won't work, because Nvidia driver will refuse to load in a VM.

woopla

I know it won't work with the Nvidia drivers, but for now I want it to start with the nouveau driver on Linux, and at least get something working.

olivierlambert

It seems someone made it with Nvidia consumer GPU passthrough: he used modded drivers that get rid of the check.

woopla

I know there are... workarounds around that (e.g. for KVM you can hide the fact that it's running inside a VM, and I believe there are similar solutions for Xen).

But first things first - I want to get rid of that default framebuffer. Is there a way to pass 'base' Xen config options through XCP-ng (e.g. with an xe command)?

MajorTom

@woopla I'm not sure if this will work in your setup, but I've thought I'll share the solution which worked for me as I tried hard to get rid of bloody framebuffer (which was making the console in XCP-ng Center and in XOA almost unreadable due to tiny or blurred font).

After many hours of googling and trying various settings in /etc/default/grub (which theoretically should work, but didn't) I found unix.stackexchange.com/questions/346090/disable-framebuffer-in-qemu-guests.

It advised:

" disable the framebuffer via a bochs_drm module parameter - i.e. via setting it on the guest kernel command line: bochs_drm.fbdev=off "

Precisely, I put into /etc/default/grub the following line:

GRUB_CMDLINE_LINUX_DEFAULT="systemd.show_status=1 bochs_drm.fbdev=off"

edit: I forgot to mention: the above line is for a VM system, not for XCP-ng host.

(The systemd entry is unrelated to fb issue, but I'm quoting it here as a additional tip - I need it to at least partially work around systemd fascist plague).

I wonder: will this bochs tip help you?

woopla

@MajorTom thanks that could be a solution. In the end I moved my single-machine Homelab to Proxmox, because I have way better control in this specific use-case - I can see IOMMU groupings and figure out which USB controller I can also passthrough. And this works fine, I'm posting this from this VM.

XCPng isn't bad, it´s just not suited to my very specific use case.

Cheers,

Clément