common/spinlock.c in Xen 4.4.x and earlier does not properly handle read and write locks, which allows local x86 guest users to cause a denial of service (write denial or NMI watchdog timeout and host crash) via a large number of read requests, a different vulnerability to CVE-2014-9066.
https://security.gentoo.org/glsa/201504-04
http://xenbits.xen.org/xsa/advisory-114.html
http://www.securityfocus.com/bid/71544
http://www.openwall.com/lists/oss-security/2014/12/08/4
http://lists.opensuse.org/opensuse-security-announce/2015-02/msg00010.html
http://lists.opensuse.org/opensuse-security-announce/2015-02/msg00005.html