linux-kernel - Re: i386 PDA patches use of %gs

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Message-ID: <20061115184433.GB5078@elte.hu>
Date:	Wed, 15 Nov 2006 19:44:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Arjan van de Ven <arjan@...radead.org>, akpm@...l.org, ak@...e.de,
	linux-kernel@...r.kernel.org, Michael.Fetterman@...cam.ac.uk,
	Ian Campbell <Ian.Campbell@...Source.com>
Subject: Re: i386 PDA patches use of %gs


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

> > that loads (and uses) a single selector value for %fs, and doesnt do 
> > any mixed use as far as i can see.
> 
> I'm not sure what you're getting at.  Each loop iteration is analogous 
> to a user->kernel->user transition with respect to the 
> save/reload/use/restore pattern on the segment register.  In this 
> case, %fs starts as a null selector, gets reloaded with a non NULL 
> selector, and then is restored to null.  Do you mean some other 
> mixing?

yeah, mixed use: i.e. set up /two/ selector values and load them into 
%gs and read+write memory through them. It might not change the results, 
but that's what i meant under 'mixed use'.

	Ingo
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