QEMU's live migration is almost in a full thread model except the loadvm process, which used to be run in the main thread since the start of when live migration feature was introduced in QEMU.  So it has been at least 10+ years like that.

This story is to track the threadify of loadvm process upstream here:

https://lore.kernel.org/all/20250827205949.364606-1-peterx@redhat.com/

For more information, please refer to the cover letter of the work.