The vmx_set_uc_mode function in Xen 3.3 through 4.3, when disabling caches, allows local HVM guests with access to memory mapped I/O regions to cause a denial of service (CPU consumption and possibly hypervisor or guest kernel panic) via a crafted GFN range.
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00010.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00011.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00021.html