The Hypervisor (aka rhev-hypervisor) in Red Hat Enterprise Virtualization (RHEV) 2.2, and KVM 83, when the Intel VT-x extension is enabled, allows guest OS users to cause a denial of service (NULL pointer dereference and host OS crash) via vectors related to instruction emulation.
https://rhn.redhat.com/errata/RHSA-2010-0627.html
https://rhn.redhat.com/errata/RHSA-2010-0622.html
https://bugzilla.redhat.com/show_bug.cgi?id=570528
http://www.vupen.com/english/advisories/2011/0012
http://secunia.com/advisories/42778
http://lists.opensuse.org/opensuse-security-announce/2011-01/msg00000.html