Comment 7 for bug 453653

To answer janusz comments -
To reassign IRQ's etc you need:
(Recompiled) Kernel with
CONFIG_DMAR=y
CONFIG_DMAR_DEFAULT_ON=y

To check your available kernels:
grep DMAR /boot.config*
If you look at other launchpad entries you will see there has been discussion on this so it might have been resolved already.
Sadly Maverick Beta does not have it set.

Apparmor set up as follows:
/etc/apparmor.d/abstractions/libvirt-qemu needs to contain

# required for IRQ remapping with PCI Pass Through
capability sys_rawio,
# For hostdev access
/sys/devices/ r,
/sys/devices/** r,

Dave