Re: [PATCH 0/5] KVM paravirt_ops implementation

Zachary Amsden
2007-06-20T20:43:03Z

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.

Unless you also migrate the hypercall page itself and impose migration
restrictions on compatible hypercall pages.

Although I favor the guarantee that execution within the hypercall page
is finished - it is important for protecting against non-reentrancy as
well. Think about interrupts during batching / queueing operations.

Zach