The do_mmu_update function in arch/x86/mm.c in Xen 3.2.x through 4.4.x does not properly manage page references, which allows remote domains to cause a denial of service by leveraging control over an HVM guest and a crafted MMU_MACHPHYS_UPDATE.
lists.opensuse.org/opensuse-security-announce/2015-02/msg00005.html
lists.opensuse.org/opensuse-security-announce/2015-02/msg00010.html
secunia.com/advisories/62672
www.debian.org/security/2015/dsa-3140
www.securityfocus.com/bid/71207
xenbits.xen.org/xsa/advisory-113.html
exchange.xforce.ibmcloud.com/vulnerabilities/98853
security.gentoo.org/glsa/201504-04