linux-kernel - Re: [PATCH 4/8] unify paravirt parts of system.h

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Message-ID: <20071217002306.GD5692@elf.ucw.cz>
Date:	Mon, 17 Dec 2007 01:23:06 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Avi Kivity <avi@...ranet.com>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	glommer@...il.com, tglx@...utronix.de, ehabkost@...hat.com,
	jeremy@...p.org, anthony@...emonkey.ws,
	virtualization@...ts.linux-foundation.org, rusty@...tcorp.com.au,
	chrisw@...s-sol.org, rostedt@...dmis.org, hpa@...or.com
Subject: Re: [PATCH 4/8] unify paravirt parts of system.h

On Mon 2007-12-17 01:27:29, Rafael J. Wysocki wrote:
> On Saturday, 15 of December 2007, Ingo Molnar wrote:
> > 
> > * Pavel Machek <pavel@....cz> wrote:
> > 
> > > > Linux never uses that register. The only user is suspend 
> > > > save/restore, but that' bogus because it wasn't ever initialized by 
> > > > Linux in the first place. It could be probably all safely removed.
> > > 
> > > It probably is safe to remove... but we currently support '2.8.95 
> > > kernel loads/resumes 2.6.24 image'... which would break if 2.8 uses 
> > > cr8.
> > > 
> > > So please keep it if it is not a big problem.
> > 
> > hm, so __save_processor_state() is in essence an ABI? Could you please 
> > also send a patch that documents this prominently, in the structure 
> > itself?
> 
> Hmm, I'm not sure if it really is an ABI part.  It doesn't communicate anything
> outside of the kernel in which it is defined.

Well, it is not "application binary interface", but it is
"kernel-to-kernel binary interface"...

> The problem is, though, that if kernel A is used for resuming kernel B, and
> kernel B doesn't save/restore everything it will need after the resume, then
> things will break if kernel A modifies that.  So, yes, we'll need to document
> that explicitly.

Agreed.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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