The get_page_from_l3e function in arch/x86/mm.c in Xen allows local 32-bit PV guest OS administrators to gain host OS privileges via vectors related to L3 recursive pagetables.
support.citrix.com/article/CTX216071
www.debian.org/security/2016/dsa-3663
www.oracle.com/technetwork/topics/security/ovmbulletinjul2016-3090546.html
www.securityfocus.com/bid/92862
www.securitytracker.com/id/1036751
xenbits.xen.org/xsa/advisory-185.html
xenbits.xen.org/xsa/xsa185.patch
security.gentoo.org/glsa/201611-09