[vfio-users] Failed to mmap 0000:01:00.0 BAR 3. Performance may be slow

[Alex Williamson]

On Sun, 19 Aug 2018 22:57:44 +0200
Konrad Eisele <eiselekd at gmail.com> wrote:

> I try to passthrough the primary graphic card (GForce 710b
> at slot 0000:01:0.0) to a win kvm guest. The host runs
> headless. I have blacklisted the nvidia drivers and bound
> the drivers to vfio-pci on startup. However when starting qemu
> I currently get the error:
> 
> (qemu) qemu-system-x86_64: -device vfio-pci,host=01:00.0,multifunction=on:
> Failed to mmap 0000:01:00.0 BAR 3. Performance
> may be slow
> 
> It seems that efifb is jumping in and allocating some region:
> 
> $cat /proc/iomem
> ...
> 0000000-00000000 : PCI Bus 0000:00
>  00000000-00000000 : PCI Bus 0000:01
>    00000000-00000000 : 0000:01:00.0
>      00000000-00000000 : vfio-pci
>    00000000-00000000 : 0000:01:00.0
>      00000000-00000000 : efifb
>  00000000-00000000 : PCI Bus 0000:03
>    00000000-00000000 : 0000:03:00.0
> ...
> 
> So I added efifb:off to grub's kernel cmdline
> 
> cat /proc/cmdline:
> .... video=vesafb:off,efifb:off
> 
> However that doesnt seem to help. Does anybody know howto
> prevent the above error?
> What more do I have to do to passthrough the primary graphics card to a
> guest
> running on a headless server? Any tips?

This is generally why it's not recommended, iterate through what's
using resources on the card until you've exhausted and disabled all
possible console drivers for your device.  You'll likely also need to
use a dumped ROM image for the card since the ROM for the primary
graphics is read from the shadow ROM space where it can be updated in
place by the execution of the ROM.  Thanks,

Alex