Comment 12 for bug 886521

I can confirm that no Ubuntu kernels (excepting some pre-Lucid) will boot on Xen4 in HVM mode if dom0 is configured to allow PCI access (the norm, and what you would want in case your guest OS's need it). What happens is early on in the boot process, the pci unplug stuff is run, resulting in /dev/sdX being unplugged. The PV drivers will not load due to no platform_pci module. So the OS will not boot. It is possible to fix this using command line magic (xen_emul_unplug=never from memory) but this is not practical in a cloud environment where users just expect their operating systems to install and run.

Another option would be putting this module in the udeb (possibly - untested).

However, every other distribution that builds in Xen4 support also puts this as a builtin. Therefore every other distro boots first time.

In my view this is a bug in Lucid, Maverick, Natty, Oneiric and Precise.