An issue was discovered in the Linux kernel before 5.9. arch/x86/kvm/svm/sev.c allows attackers to cause a denial of service (soft lockup) by triggering destruction of a large SEV VM (which requires unregistering many encrypted regions).
Reference and upstream patch:
Created kernel tracking bugs for this issue:
Affects: fedora-all [bug 1947996]
This was fixed for Fedora with the 5.9 kernel rebases.
For a general description of what a CPU soft lockup is, refer to https://access.redhat.com/articles/371803.