VMX in Xen 4.6.x and earlier, when using an Intel or Cyrix CPU, allows local HVM guest users to cause a denial of service (guest crash) via vectors related to a non-canonical RIP.
lists.fedoraproject.org/pipermail/package-announce/2016-February/177990.html
lists.fedoraproject.org/pipermail/package-announce/2016-March/178518.html
support.citrix.com/article/CTX209443
www.debian.org/security/2016/dsa-3519
www.securitytracker.com/id/1035043
xenbits.xen.org/xsa/advisory-170.html
security.gentoo.org/glsa/201604-03