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

[tgh <tianguanhua@ncic.ac.cn>]

Thank you for your reply

Thank you


Mark Williamson 写道:
> Nb. I'm focussing on x86 (and x86_32 where appropriate) here and have been in 
> the rest of the thread (unless otherwise specified)...  other architectures 
> deal with pseudophysical addressses differently.
>
>   
>> Mark Williamson 写道:
>>     
>>>> 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).
>>>       
>> Is there this kind paravirtual os for xen at present?
>> or in future,will this kind paravirtual os come out?
>> and what is the advantages for this kind of os?
>>     
>
> There's two aspects to this answer, I guess:
>
> 1) Will guests which maintain their own pseudophysical abstraction rather than 
> using Xen's be written?  /  Will Xen's pseudophysical support be removed?
>
> This isn't likely for the timebeing; Xen needs to incorporate the 
> pseudophysical support it has for backwards-compatibility purposes and given 
> that there's no reason for guests not to use it.
>
> 2) Will guests that don't use a pseudophysical abstraction at all be written?
>
> I don't know if anyone has written / ported an OS that does this...  I 
> wouldn't expect to see any general purpose OSes using this for a while - they 
> typically seem to need the pseudophysical abstraction to keep their generic 
> memory management code happy.
>
> More minimal, special purposes OSes (especially if targetted to Xen) might be 
> able to do away with pseudophysical addresses entirely and just use virtual 
> and machine addresses.
>
> Cheers,
> Mark
>
>