Hi,

My goal is to assign PCI addresses to a number of devices (network interfaces, disks and PCI devices in PCI-passthrough) without delegating to libvirt the generation of those values. This should give me more control and for sure more predictability over the hardware configuration of a virtual machine and consequently the name of the interfaces in it.  I'm using libvirt 4.3.0 to create qemu/KVM virtual machines running Linux (Debian Stretch).

So, for every device of the type mentioned above, I add this line:
<address type='pci' domain='0x0000' bus='0x__' slot='0x__' function='0x0'/>,

... with values from 00 to ff in the bus field, and from 00 to 1f in the slot field, as described in the documentation.

Long story short, I noticed that as soon as I assign values > 0x09 to the bus field, the serial console hangs indefinitely, in both Debian and Ubuntu. The VM seems to be started correctly and its state is "running"; in the XML file created by libvirt, I see all controllers from 0 the largest bus value I assigned, so everything from that side seems ok.