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

[Alex John]

On Sun, Aug 19, 2018 at 10:57:44PM +0200, Konrad Eisele 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

Have you checked if you have a PCI bridge connecting to your graphics card in
the same IOMMU group? Or any other device?

In that case you should not be able to reserve memory at all, but no harm
checking.

>
> 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?

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