Re: [Xen-devel] Re: [RFC, PATCH 5/24] i386 Vmi code patching

[Stefan Berger <stefanb@xxxxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 03/23/2006
06:45:54 PM:

> Keir Fraser wrote:
> > We could extend the concept of the interface shim we already
have -- a 
> > set of OS-specific high performance shims, plus a fallback OS-agnostic
> > shim.
> 
> Currently the lack of a shim is the key difference between the VMI
and 
> Xen approaches. Forgive me for summarizing, but I'm not sure it's
been 
> made clear. The VMI is the interface between the OS and a shim layer--it
> is not a hypervisor interface. The kernel makes VMI calls to the shim
> and the shim makes hypercalls, if needed, to the hypervisor.
> 
>      VMI            
      VMI native            Xen/Xen
native
> 
> 
>       OS            
         OS          
          OS
> -------------- VMI      -------------- VMI
>    Shim (ROM)
> -------------- HV API              
           -------------- HV API
>    Hypervisor            
 Native HW              Hypervisor
> 

Although this is about VMI, one should not loose sight
of this one here with an unmodified OS on virtualizeable hardware:


      Native


        OS

----------------
    Hypervisor


I think building this could actually be the driving
force that can dictate *a lot* of what happens in 'Hypervisor' and what
by that implementation alone is offered to the OS by 'Hypervisor' in terms
of components. It would necessarily have to end up being a 'PC emulator'.
Parts of that Hypervisor architecture can then also be made available to
interface with the ROM shown above - not that this has not been done for
Xen, but the Qemu models seem to be very far away in domain 0. Xen in contrast
has been optimized for speed. I wonder whether the two goals of performanc
and PC emulaton are in fact mutually exclusive.

  Stefan

> 
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