I am attempting to get a PV domU guest (Ubuntu Trusty Tahr 14.04) running on XenServer 6.5 running DevStack Kilo to passthrough a GPU to an instance using the pci_alias assignment.

I can see the GPU on the DevStack VM with lspci -nn:

00:00.0 3D controller [0302]: NVIDIA Corporation GK110BGL [Tesla K40c]

IOMMU is also enabled on the DevStack VM: dmesg | grep -iE "dmar|iommu"

 [    0.000000] Command line:
 root=/dev/mapper/stack--vg-root ro
 console=hvc0 splash quiet
 intel_iommu=on $vt_handoff -- quiet
 console=hvc0

 [366537.439789] Kernel command line:
 root=/dev/mapper/stack--vg-root ro
 console=hvc0 splash quiet
 intel_iommu=on $vt_handoff -- quiet
 console=hvc0

[366537.439849] Intel-IOMMU: enabled

I used the following for the nova.conf configuration:

 pci_passthrough_whitelist = [{"vendor_id":"10de","product_id":"1024"}]
 pci_alias = {"vendor_id":"10de","product_id":"1024","name":"K40c"}
 scheduler_available_filters = nova.scheduler.filters.all_filters
 scheduler_available_filters = nova.scheduler.filters.pci_passthrough_filter.PciPassthroughFilter
 scheduler_default_filters = PciPassthroughFilter

Using the Flavor type m1.small I was able to create an instance. Then I terminated it and added the pci_alias to m1.small with "nova flavor-key m1.small set pci_passthrough:alias=K40c:1" and attempted to create it again and get the following error in the n-cpu log:

 File "/usr/local/lib/python2.7/dist-packages/libvirt.py", line 3263, in defineXML libvirtError:
 internal error: Insufficient specification for PCI address

The only difference in the two XMLs passed to defineXML seem to be the addition of:

<hostdev mode="subsystem" type="pci" managed="yes">
   <source>
      <address bus="0x00" domain="0x0000" function="0x0" slot="0x00"/>
   </source>
</hostdev>