The XEN_DOMCTL_memory_mapping hypercall in Xen 3.2.x through 4.5.x, when using a PCI passthrough device, is not preemptible, which allows local x86 HVM domain users to cause a denial of service (host CPU consumption) via a crafted request to the device model (qemu-dm).
https://security.gentoo.org/glsa/201504-04
http://xenbits.xen.org/xsa/advisory-125.html
http://www.securitytracker.com/id/1031994
http://www.securityfocus.com/bid/73448
http://lists.opensuse.org/opensuse-security-announce/2015-05/msg00018.html
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00014.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-April/155198.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-April/154579.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-April/154574.html