Take a look at http://wiki.xensource.com/xenwiki/VTdHowTo Two things in particular about PCI passthrough: - Only devices with FLR capabilities are supported. - Some motherboards are buggy. They advertised that they support Vt-d but do not correctly handle it (those with a broken ACPI DMAR table) I think lspci -vv will tell you if the device supports FLR. It will show 'FLReset+' I believe.