Comment 19 for bug 791364

As I wrote before, this bug should be gone since linux-image-3.0.0-10. So you might try an oneiric release install medium. Be aware though, that oneiric release has problems when you try to install in hvm mode, since the xen-platform-pci seems to be missing and therefore you won't see any disks or ethernet devices once those are unplugged by xen.
Your options are:
- upgrading from earlier versions and putting the xen-platrofm-pci, xen-blkfront, xen-netfront modules in the initial ramdisk.
- boot from the oneiric install medium with kernel parameter xen_emul_unplug=never, install from there with the qemu emulated devices, put the modules mentioned above in your initrd and then boot without the parameter to have pv-on-hvm functionality.