Re: [Xen-devel] question about the meaning of memory auto-translate and paravirtual and no pseudophysical overlay

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Mark Williamson 写道:
> > This would be a guest that didn't use the abstraction of pseudophysical
> > addresses at all; it would just use virtual and (real) machine
> > addresses.  I'm not sure if there are any guests that operate in this
> > way...  Certainly the major heavyweight OSes all use this technique when
> > paravirtualised.
>
> what is the major heavyweight OSes?

I was referring to the full general purpose OSes that have been ported to Xen, 
i.e.: Linux, NetBSD, Solaris, etc.

> and how does it paravirtualise? 

These all use pseudophysical addresses to maintain the abstraction of a 
vaguely "normal" memory model for their core memory management code to work 
with, then the Xen architecture code in each OS translates these into real 
machine addresses so that everything works properly.

> if there is no pseudophysical addresses,a physical host computer could
> only paravirtualise one VM,is it right?

No, AFAIK pseudophysical addresses are mostly there for the convenience of the 
guest.  Xen has some support for them so that guests can use them more 
efficiently but that's not strictly necessary.  In principle, they could be 
eliminated from Xen entirely (would require modifying the PV guests to manage 
the pseudophys abstraction themselves).

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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