xen-kernel -- CPU lockup during exception delivery

The Xen Project reports:

A malicious HVM guest administrator can cause a denial of service.
Specifically, prevent use of a physical CPU for a significant,
perhaps indefinite period. If a host watchdog (Xen or dom0) is in
use, this can lead to a watchdog timeout and consequently a reboot
of the host. If another, innocent, guest, is configured with a
watchdog, this issue can lead to a reboot of such a guest.