Re: [PATCH 0/5] KVM paravirt_ops implementation

["H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>]

Jeremy Fitzhardinge wrote:
> 
>> The completely identical device model is of course ideal, but the
>> implementation and consolidation of that is a long term prospect to
>> move towards, not something that will happen immediately.  We at least
>> emulate physical hardware devices already, and will continue to need
>> drivers compatible with those models for some time.
> 
> Well, physical devices and completely emulated physical devices are
> fairly straightforward - do it like real hardware.  Its the semi-virtual
> devices which pose problems.  Either device emulations with a bit of
> performance paravirtualization sprinkled over them, or virtualization
> friendly devices which allow safe direct guest access, but need some
> paravirtual management interfaces as well.
> 

Those can still be detected by appearing in the PCI configuration space,
though.  It doesn't mean they actually have to emulate a PCI device.

One of the "nice" things (from a virtualization perspective) is that
there isn't a pan-architectural way to get to PCI config space, so on
platforms where PCI is irrelevant, it can be implemented as a
virtualization call.

Multistandard devices obviously need to model real hardware more
accurately, since that's the common denominator.

	-hpa

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