I absolutely agree with both of your point of view. But what's the
alternative ?
Ideally we should fail/stop migration even if a single guest page
encryption status cannot be notified and that should be the way to
proceed in this case, the guest kernel should notify the source
userspace VMM to block/stop migration in this case.
From a practical side, i do see Qemu's migrate_add_blocker() interface
but that looks to be a static interface and also i don't think it will
force stop an ongoing migration, is there an existing mechanism
to inform userspace VMM from kernel about blocking/stopping migration ?