RFC: Fast Migration for SEV and SEV-ES - blueprint and proof of concept

[Tobin Feldman-Fitzthum <tobin@linux.ibm.com>]

Hello,

Dov Murik, James Bottomley, Hubertus Franke, and I have been working on 
a plan for fast live migration with SEV and SEV-ES. We just posted an 
RFC about it to the edk2 list. It includes a proof-of-concept for what 
we feel to be the most difficult part of fast live migration with SEV-ES.

https://edk2.groups.io/g/devel/topic/77875297

This was posted to the edk2 list because OVMF is one of the main 
components of our approach to live migration. With SEV/SEV-ES the 
hypervisor generally does not have access to guest memory/CPU state. We 
propose a Migration Handler in OVMF that runs inside the guest and 
assists the hypervisor with migration. One major challenge to this 
approach is that for SEV-ES this Migration Handler must be able to set 
the CPU state of the target to the CPU state of the source while the 
target is running. Our demo shows that this is feasible.

While OVMF is a major component of our approach, QEMU obviously has a 
huge part to play as well. We want to start thinking about the best way 
to support fast live migration for SEV and for encrypted VMs in general. 
A handful of issues are starting to come into focus. For instance, the 
target VM needs to be started before we begin receiving pages from the 
source VM. We will also need to start an extra vCPU for the Migration 
Handler to run on. We are currently working on a demo of end-to-end live 
migration for SEV (non-ES) VMs that should help crystallize these 
issues. It should be on the list around the end of the year. For now, 
check out our other post, which has a lot more information and let me 
know if you have any thoughts.

-Tobin