Re: [PATCH 0/5] KVM paravirt_ops implementation

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

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