An issue was discovered in Xen through 4.11.x on AMD x86 platforms, possibly allowing guest OS users to gain host OS privileges because TLB flushes do not always occur after IOMMU mapping changes.
https://xenbits.xen.org/xsa/advisory-275.html
https://www.debian.org/security/2019/dsa-4369
https://support.citrix.com/article/CTX239432
https://lists.debian.org/debian-lts-announce/2019/10/msg00008.html
http://www.securityfocus.com/bid/106182
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00072.html