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.
https://security.gentoo.org/glsa/201611-09
http://support.citrix.com/article/CTX216071
http://www.debian.org/security/2016/dsa-3663
http://www.oracle.com/technetwork/topics/security/ovmbulletinjul2016-3090546.html
http://www.securitytracker.com/id/1036751