Re: [PATCH 26/34] accel/mshv: introduce SaveVMHandler

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Thu, Jul 02, 2026 at 10:50:17AM +0200, Paolo Bonzini wrote:
> Il ven 17 apr 2026, 12:58 Magnus Kulke <magnuskulke@linux.microsoft.com> ha
> scritto:
> 
> > This mechanism is used to handle more imperative partition-wide steps
> > that have to be taken as part of a migration routine.
> >
> > Currently it's a skeleton that will just pause/resume the partition as
> > part of a migration. It will later be extended with more specific steps
> > like reference time and hypercall pages.
> >
> 
> Sorry, I forgot to reply about this one.

> 
> It is not clear why you need to pause, since this is handled by common
> code. Are you not handling live migration yet? That should be handled at
> levels above QEMU, because users expect migration to be performed while the
> VM runs, and the SaveVMHandler should just fail migration of the VM is
> running.

Oh, good catch, thanks. I misunderstood something about those hooks
apparently. I think this was originally inspired by migration logic in
Cloud-Hypervisor, which freezes/unfreezes a partition during migration
- but only after the pre-copy phase is done.

I assumed the hooks were also called only before the final delta is
transmitted. In tests I was relying on the reported state of the source
from QMP, which probably can not accurately reflect the state of the
partition as the freeze/unfreeze happens out of band (i.e. is is not
orchestrated by the migration framework).

I'll have to research a bit and see if there are more appropriate hooks,
or if we don't need to freeze the source partition at all.

best,

magnus