[vfio-users] What makes or breaks proper unbinding of vfio-pci?

[Okky Hendriansyah]

> On Jan 26, 2016, at 07:29, Mario Goebbels <me at tomservo.cc> wrote:
> 
> Small update. I managed to figure out an alternative way to unbind the graphics device properly and reuse it back on the host. Instead of directly unbinding it, I just remove the device(s) and then rescan the PCI bus. Like this:
> 
> echo > /sys/bus/pci/devices/${DEV}/driver_override
> echo 1 > /sys/bus/pci/devices/${DEV}/remove
> echo 1 > /sys/bus/pci/rescan
> 
> Seems to work reliably (for now, knocking on wood).
> 
> Regards,
> -mg

Hi Mario,

Sorry since this is probably a bit out of topic, I just noticed that you passed-through your primary VGA adapter (first slot) to your VM, is it correct? How do you pass the framebuffer that is occupying the primary VGA adapter since the host boot? 

My platform is similiar to yours, but different board, ASUS X99-A. Currently I have Galax GT 610 as my primary VGA adapter for the host, and Gigabyte GTX 980 for my guest VM in the second slot. But since my board's second physical x16 slot only operates in x8 when using i7-5820K, I intend to move my Gigabyte GTX 980 to the primary slot, hopefully to have an even better juice out of it.

Is it possible to let the host boot borrowing the primary VGA initial display (GTX 980) and move the host display to the secondary card (GT 610) once the  host is fully booted and enters desktop session?

I have disabled the efifb from the kernel command line and made a GPU reset forcefully by starting a dummy guest VM that passes through the primary VGA but with incorrect QEMU parameters so it will exit itself but with GPU already reset (I think, since the framebuffer initial display went blank).

I also have moved the X session to the GT 610, by not having the GTX 980 participate on the host X display. But somehow when I start the real guest VM, the display just blank.

Care to shed some light to me?

Thank you.

Best regards,
Okky Hendriansyah