Problem with Ubuntu 16.04 PV clients

[Mark Davies <mark%ecs.vuw.ac.nz@localhost>]

Hi,
   I can successfully get a ubuntu 14.04 domu running on a 
NetBSD-7.0_STABLE/amd64 Xen4.2 dom0, as I can a current ArchLinux domu 
running (and lots of NetBSD domu's) but if I try to start a ubuntu 16.04 
domu it gets as far as

   [...]
[    0.204716] uhci_hcd: USB Universal Host Controller Interface driver
[    0.204757] i8042: PNP: No PS/2 controller found. Probing ports directly.
[    1.205919] i8042: No controller found
[    1.205973] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 
0x24098198f58, max_idle_ns: 440795204786 ns

and then stops.

Anyone got a 16.04 client running?  Knows whats going on?

cheers
mark