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

To: Eli Collins <ecollins@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [RFC, PATCH 5/24] i386 Vmi code patching
From: Stefan Berger <stefanb@xxxxxxxxxx>
Date: Thu, 23 Mar 2006 22:26:49 -0500
Cc: Linus Torvalds <torvalds@xxxxxxxx>, Wim Coekaerts <wim.coekaerts@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Christopher Li <chrisl@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Anne Holler <anne@xxxxxxxxxx>, Jyothy Reddy <jreddy@xxxxxxxxxx>, xen-devel-bounces@xxxxxxxxxxxxxxxxxxx, Kip Macy <kmacy@xxxxxxxxxxx>, Ky Srinivasan <ksrinivasan@xxxxxxxxxx>, Leendert van Doorn <leendert@xxxxxxxxxxxxxx>
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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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