Memory leak in Xen 3.3 through 4.8.x allows guest OS users to cause a denial of service (ARM or x86 AMD host OS memory consumption) by continually rebooting, because certain cleanup is skipped if no pass-through device was ever assigned, aka XSA-207.
https://xenbits.xen.org/xsa/advisory-207.html
https://lists.debian.org/debian-lts-announce/2018/09/msg00006.html