[vfio-users] "Device or Resource Busy"

[Alex Williamson]

On Wed, Mar 16, 2016 at 6:42 AM, Bryan Jacobs <bryanrj at gmail.com> wrote:

> Hello VFIO users!
>
> Yesterday I was able to boot a Windows VM successfully with OVMF and a
> passed-through graphics card.
>
> I'm not sure what changed, but today I get a libvirt qemu log full of
> these messages:
>
> "qemu-system-x86_64: vfio_region_write(0000:01:00.0:region1+0x240c14,
> 0xffffffff,4) failed: Device or resource busy"
>
> There are hundreds upon hundreds of these - it looks like it's walking a
> large memory space, doing reads and writes, and failing every time. The
> graphics card gives code 43, but the problem doesn't go away even if I
> entirely disable enlightenments. Removing the PCIe passthrough devices gets
> rid of the log entries.
>
> My two passed PCI devices are a GTX 980TI GPU and its HDMI audio function.
> They are in their own IOMMU group with their own pci bridge. The CPU is an
> i5-6600k.
>
> I have verified that the devices are bound to the vfio-pci driver,
> although I don't seem to be able to entirely stop console output from
> appearing on the graphics card on boot (not even with my CSM-free UEFI set
> to use the integrated graphics instead). There's definitely nothing like X
> running, and the nvidia module is unloaded in the host OS.
>
> # virsh --version
> 1.3.2
> # uname -a
> Linux host 4.4.5-1-ARCH #1 SMP PREEMPT Thu Mar 10 07:38:19 CET 2016 x86_64
> GNU/Linux
>
> Removing the passed-through device fixes the issue.
>
> What would make the vfio_region_(read|write) calls return EBUSY? I figured
> I'd ask here before diving into the kernel sources :-/.
>

This is likely due to another driver in the host claiming some of the
resources of the device.  Check /proc/iomem to see if there are other
drivers making use of some device regions.
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