A guest which sets a VCPU with an inappropriate deadline can cause an infinite loop in Xen, blocking the affected physical CPU indefinitely.
A malicious guest administrator can trigger the bug. If the Xen watchdog is enabled, the whole system will crash. Otherwise the guest can cause the system to become completely unresponsive.
Acknowledgements:
Red Hat would like to thank the Xen project for reporting this issue.
Statement:
This issue did affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5.
This issue did not affect Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG as we did not have support for Xen hypervisor.