An issue was discovered in Xen 4.8.x through 4.11.x allowing x86 PV guest OS users to cause a denial of service because mishandling of failed IOMMU operations causes a bug check during the cleanup of a crashed guest.
https://xenbits.xen.org/xsa/advisory-291.html
https://www.debian.org/security/2020/dsa-4602
https://seclists.org/bugtraq/2020/Jan/21