Hello, I was reading the KVM documentation that mentions live-migrating an L1 guest with a running L2 guest on AMD systems results in undefined behavior: https://www.kernel.org/doc/html/latest/virt/kvm/x86/running-nested-guests.html#live-migration-with-nested-kvm. However, we noticed that this documentation hasn't been updated in a while (last edit of that section was May 6 2020 according to the blame), and notably there have been some AMD nested migration improvements in June 2020: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=039aeb9deb9291f3b19c375a8bc6fa7f768996cc. We did some stress testing of live migrating systems with nested VMs on AMD and noticed that they seem to be running fine with no crashes so far. Do we know if the docs are stale on this? If we have tested this and it seems to work fine, are we taking on a lot of risk by live migrating VMs with L2 vms running inside of them on AMD? Are there specific workloads that are known to result in undefined behavior more frequently? We have tested 2 scenarios: KVM running in KVM, and Hyper-V in KVM, both on AMD EPYC CPUs. Both seem to do fine with repeated live migrations although we are yet to try this long-term. Thanks!
