Comment 3 for bug 832207

This patch seems to solve the primary issue. It is not yet, anywhere upstream as far as I know. So it may cause other side effects or get changed before it is finally submitted.
With this applied I was able to boot pre-3.0 kernels as HVM guests under Oneiric again. However booting an Oneiric guest triggers the same issues with a change enabling IPI events and Xen spinlocks. This time the 4.1.1 hypervisor is supposed to support them.