Re: [PATCH 0/5] KVM paravirt_ops implementation

Jeremy Fitzhardinge
2007-06-20T20:33:30Z

Anthony Liguori wrote:
> I've been thinking about this wrt the hypercall page in KVM. The
> problem is that in a model like KVM (or presumably VMI), migration
> gets really difficult if you have anything but a trivial hypercall
> page since the hypercall page will change after migration.
>
> If you cannot guarantee the guest isn't executing code within the
> hypercall page (or in your case, doing something with paravirt_ops),
> then you cannot safely migrate.

Hm, you need to quiesce the kernel in some way when you do a migrate, so
making sure it isn't in a hypercall would be just part of that. In
general you'd make sure all but one CPU is parked somewhere, and the
remaining CPU is doing the suspend, right?

The tricky part for Xen in all this is how to make sure all mfn
references are visible to the hypervisor/toolstack so they can be
remapped; hypercall page contents are not a concern by comparison.

J