linux-kernel - Re: Xen & VMI?

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Message-ID: <20070306092636.GC26073@elte.hu>
Date:	Tue, 6 Mar 2007 10:26:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Zachary Amsden <zach@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization <virtualization@...ts.osdl.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, Jan Beulich <jbeulich@...ell.com>
Subject: Re: Xen & VMI?

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> You could come up with some shim layer which makes the two interfaces 
> appear similar, and you could spell the name of that shim "VMI".  Or 
> you could call it "paravirt_ops", which is the name we chose.  And you 
> could implement the interface to that layer as a binary ABI, or you 
> could make it a normal source-level Linux kernel interface, which is 
> what we chose to do.

i think you are missing my point.

paravirt_ops is a Linux-internal abstraction that tries to make our life 
easier but it has no relevance whatsoever to an external hypervisor - be 
that Xen, VMWare/ESX or Windows/Longhorn.

What matters is the /ABI/ that the hypervisor uses to talk to a Linux 
guest. In the VMWare/ESX case that's VMI. In the Xen case that's the 
hypercall page call-table ABI or the legacy int $0x82 ABI.

My suggestion would be for Linux to make only a /single/ external ABI 
promise: VMI. (and we can extend it with higher-level paravirt ops, 
etc.)

paravirt_ops has ZERO relevance here... Anyone who suggests that 
paravirt_ops somehow magically hides the ABIs that are behind it (and 
its effects on Linux) is smoking something real funny ;-)

	Ingo
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