Re: [Qemu-devel] About qemu emulation speed (a question) and supported OS

[Anthony Liguori]

Mark Williamson wrote:

> > > No, I got the impression that Fabrice was taking about virtualization the
> > > way VMware, old plex86, and vmbear (new FOSS x86 virtualizer in the
> > > works) do it.
> > >      
> > The x86 cannot be "virtualized" in the Popek/Goldberg sense, so there's
> > a couple of fast emulation techniques that are possible.  Other than a
> > hand coded dynamic translator, I reckon qemu + kqemu is about as good as
> > it can get (unless I'm missing something here).  Do you have
> >    
>
> Well, VMware does manage direct execution of some kernel code, I believe.  
> VMware's real super-cunningness is doing this as much as they can, instead of 
> emulating all the stuff.  That said, I think with suitable optimisations 
> emulating all the kernel code could be acceptable.
>
> The unfortunate thing is that the guest can still tell it's in a VMware 
> machine (I'm not clear how) so it's not really *full* virtualisation, it's 
> just about epsilon away from it :-)  VT / SVM will solve this properly.
>  
I reckon kqemu has this same problem... Technically, even in ring 3, if 
you run natively, you violate the Popek/Goldberg requirements because of 
cpuid.  It's just not possible to trap it but it shouldn't matter for 
most software.

> They have a (crazy but cool) idea that they'll one day be able to live-migrate 
> (i.e. without more than a few hundred ms downtime) virtual machines between 
> L4 hypervisors and Xen hypervisors.
>  
Yeah, how cool is that :-)

Regards,

Anthony Liguori

> Cheers,
> Mark
>
>  
>
> > > > FWIW, Xen is already using QEMU in this way.  It would be very neat to
> > > > see this technique applied to a Type II VMM.
> > > >        
> > > Do you have any details on this?
> > >      
> > Mark did a really good job of summarizing the current architecture.
> >
> > Regards,
> >
> > Anthony Liguori
> >
> >    
> >
> > > > Regards,
> > > >
> > > > Anthony Liguori
> > > >
> > > >
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