Ouch -- I wonder how cloud providers will respond to this. Rolling updates across all their boxes to update the Xen hypervisors? Think about the magnitude of the problem if your someone like Rackspace/Linode/Slicehost/AWS!?
Does anyone have an exploit / test for this?
(I don't necessarily want an exploit; I just want to know if it's feasible in our various hosted and non-hosted environments)