RE: [Xen-devel] Different instruction stream for PV OS on VT/Pacifica?

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Magenheimer, Dan (HP Labs Fort Collins)
> Sent: 28 April 2006 17:27
> To: xen-devel
> Subject: [Xen-devel] Different instruction stream for PV OS 
> on VT/Pacifica?
> 
> I was asked a question and I think I know the answer for
> Xen/ia64 but am not sure I know the answer for Xen/x86 -- or 
> if there is a different answer for VT vs Pacifica.
> 
> In the three scenarios:
> A. Paravirtualized (PV) OS running on a pre-HVM processor
>    using a virtualization-capable Xen
> B. PV OS running on a VT (or Pacifica) processor using a
>    virtualization-capable Xen but NOT running any fully
>    virtualized (FV) OS
> C. PV OS running on a VT (or Pacifica) processor using a
>    virtualization-capable Xen which is sharing the processor
>    with a FV OS
> 
> is the sequence of instructions executed by the processor on 
> behalf of the PV OS -- including instructions in firmware and 
> in Xen -- identical or different/faster/slower?  (Ignoring 
> irrelevant factors such as domain switch, non-virtualization- 
> related processor differences, etc.)
> 
> On Xen/ia64, a PV OS should always execute the same sequence 
> of instructions, whether or not it is on a VT-capable processor.
> 
> Can experts for the others (VT-x and Pacifica) comment?

I'd say that this answer applies to AMD processors (and as far as I know
it applies to Intel too - but I'm not really a spokesperson for AMD, and
even less so for Intel.)

There's been some thinking that we could use HVM (VT/SVM (pacifica)) to
enhance PV guest too, but so far nothing has been implemented [and I
guess once it does get implemented, IA64 will follow shortly afterwards,
assuming it's generally useful and not specific to x86]. 

--
Mats
> 
> Thanks,
> Dan
> 
> 
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