The guest_physmap_mark_populate_on_demand function in Xen 4.2 and earlier does not properly unlock the subject GFNs when checking if they are in use, which allows local guest HVM administrators to cause a denial of service (hang) via unspecified vectors.
https://exchange.xforce.ibmcloud.com/vulnerabilities/80483
http://www.securityfocus.com/bid/56803
http://www.openwall.com/lists/oss-security/2012/12/03/12
http://www.debian.org/security/2012/dsa-2582
http://support.citrix.com/article/CTX135777
http://security.gentoo.org/glsa/glsa-201309-24.xml
http://secunia.com/advisories/55082
http://secunia.com/advisories/51487
http://secunia.com/advisories/51486
http://secunia.com/advisories/51468
http://secunia.com/advisories/51397
http://lists.opensuse.org/opensuse-updates/2013-04/msg00052.html
http://lists.opensuse.org/opensuse-updates/2013-04/msg00051.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00021.html
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00011.html
http://lists.opensuse.org/opensuse-security-announce/2012-12/msg00019.html
http://lists.opensuse.org/opensuse-security-announce/2012-12/msg00018.html
http://lists.opensuse.org/opensuse-security-announce/2012-12/msg00001.html