When running an HVM domain in Populate-on-Demand mode, Xen would
sometimes search the domain for memory to reclaim, in response to
demands for population of other pages in the same domain. This
search runs without preemption. The guest can, by suitable
arrangement of its memory contents, create a situation where this
search is a time-consuming linear scan of the guest's address
space.
A malicious HVM guest administrator can cause a denial of service.
Specifically, prevent use of a physical CPU for a significant
period.