Xen 3.3.x through 4.5.x and the Linux kernel through 3.19.1 do not properly restrict access to PCI command registers, which might allow local guest OS users to cause a denial of service (non-maskable interrupt and host crash) by disabling the (1) memory or (2) I/O decoding for a PCI Express device and then accessing the device, which triggers an Unsupported Request (UR) response.
git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=af6fc858a35b90e89ea7a7ee58e66628c55c776b
lists.opensuse.org/opensuse-security-announce/2015-04/msg00001.html
lists.opensuse.org/opensuse-security-announce/2015-09/msg00004.html
lists.opensuse.org/opensuse-security-announce/2015-09/msg00018.html
lists.opensuse.org/opensuse-security-announce/2015-09/msg00021.html
www.debian.org/security/2015/dsa-3237
www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
www.securityfocus.com/bid/73014
www.securitytracker.com/id/1031806
www.securitytracker.com/id/1031902
www.ubuntu.com/usn/USN-2631-1
www.ubuntu.com/usn/USN-2632-1
www1.huawei.com/en/security/psirt/security-bulletins/security-advisories/hw-423503.htm
xenbits.xen.org/xsa/advisory-120.html
bugzilla.redhat.com/show_bug.cgi?id=1196266
github.com/torvalds/linux/commit/af6fc858a35b90e89ea7a7ee58e66628c55c776b
lists.fedoraproject.org/pipermail/package-announce/2015-April/155804.html
lists.fedoraproject.org/pipermail/package-announce/2015-April/155854.html
lists.fedoraproject.org/pipermail/package-announce/2015-April/155908.html
lists.fedoraproject.org/pipermail/package-announce/2015-March/152747.html
seclists.org/bugtraq/2019/Aug/18