[3.2.1] VT-d and "nested PCI bridge not supported"

["Jefferson E. Noxon" <jeff@planetfall.com>]

Hi gang,

Xen emits the following message when I boot up with vtd enabled:

(XEN) [VT-D]intel-iommu.c:1202:d32767 context_context_mapping: nested 
PCI bridge not supported: bdf = 0:1c:1 sec_bus = 2 sub_bus = 3

I am trying to pass a PCI-e USB controller to an HVM guest.  The 
controller is on bus 3; its PCI-e to PCI bridge is bus 2.

The domU crashes when it tries to access these devices.

Unfortunately there are no native PCI-e USB controllers.

Is this a limitation of Xen, or a limitation of VT-d?  If the former, is 
anyone working on a fix?  Perhaps there is something I can do to get 
this working?  I would not mind if I had to assign the entire bridge to 
a domU.

Thanks!