Re: paravirtualization structure

Omar Khan
2007-02-20T00:47:34Z

Dor Laor <dor.laor@...> writes:

>
> Theoretically speaking the answer is yes, vmcall is a special
> instruction that it one and only purpose is the exit from the guest.
> While mov cr3 instruction might be bound to other actions of the
> processor and might have more effects on the pipeline, this harder to
> optimize for vmexit purposes.
>

I guess what is confusing me is that the vmcall causes an vmexit in VMX non-root
mode (the one in which a paravirtualized guest is operating), but Avi says that
a hypercal (made using a vmcall) 'avoids' a vmentry/vmexit and Ingo comments in
his patch that :

"This utilizes the cr3 filter capability of the hardware - if this works out
then no VM exit happens"

NO VM-exits happen. hmmmm... maybe I need to go over the intel manuals more
thoroughly, however any hints will be most welcomed.

Thanks

Omar