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

[Alex Williamson]

On Mon, 20 Aug 2018 12:34:37 +0800
Alex John <alex at stty.io> wrote:

> 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.

This doesn't make any sense.  A driver can certainly reserve device
resources regardless of the device being downstream of a bridge.
Thanks,

Alex