[vfio-users] Passthrough VGA on first slot

Alex Williamson alex.williamson at redhat.com
Fri Oct 2 14:25:07 UTC 2015

On Fri, 2015-10-02 at 10:00 -0300, Pedro Henrique Lara Campos wrote:
>  Hello masters of vfio. I've been playing with vfio for 3 weeks now, and
> here is a resume of what i got: When I put my loved GTX780 on the second
> pci-e slot of my GA-970A-DS3P everything works on Windows (guest) while my
> Linux (host) stays comfortable with a Radeon HD 6670.
> But, as I wouldn't be writing this email if nothing was wrong, my second
> pci-e slot is "PCIEX4" only, I believe that's because my FPS goes down and
> HDMI audio keeps crackin. I had to change the slots, my bios doesn't have
> an option to choose which GPU to use, so it uses the GTX, GRUB does it too,
> then gpu gets binded by modprobe and I have no video until XOrg starts on
> Radeon, if I start qemu, I've get:
>   "vfio_ecap_init: 0000:01:00.0 hiding ecap 0x19 at 0x900"
>   "BAR 3 mmap unsupported. Performance may be slow"
>   "vfio-pci 0000:01:00.0: Invalid ROM contents"
> No video on GTX, Windows boots normally, I can even hear notifications
> sounds, I can turn it off through "system_powerdown".
> Tried using a romfile, it only makes the third message goes away, no other
> thing changes...

If you look in /proc/iomem, you'll probably find something like vesafb
using regions of your video card.  That's the reason for the mmap
problem.  The invalid ROM contents issue is because the boot VGA ROM is
handled differently from other device ROMs and you're actually seeing a
shadow copy of it that might be modified.  The solution here is to pass
a known good ROM image via a file.  Passing primary graphics is
troublesome, which is why it's not used much or really supported.  IME,
Gigabyte boards are typically the best at allowing boot VGA selection,
so it's disappointing that your system is showing otherwise.  Thanks,


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