linux-kernel - Re: [patch 02/11] PAT x86: Map only usable memory in x86

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Message-ID: <alpine.LFD.1.00.0801101303570.3148@woody.linux-foundation.org>
Date:	Thu, 10 Jan 2008 13:05:08 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
cc:	ak@....de, ebiederm@...ssion.com, rdreier@...co.com,
	gregkh@...e.de, airlied@...net.ie, davej@...hat.com, mingo@...e.hu,
	tglx@...utronix.de, hpa@...or.com, akpm@...ux-foundation.org,
	arjan@...radead.org, jesse.barnes@...el.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [patch 02/11] PAT x86: Map only usable memory in x86_64 identity
 map and kernel text



On Thu, 10 Jan 2008, venkatesh.pallipadi@...el.com wrote:
>
> x86_64: Map only usable memory in identity map. All reserved memory maps to a
> zero page.

I don't mind this horribly per se, but why a zero page?

Accessing that page without mapping it explicitly would be a bug with 
your change - if only because you'd get the wrong value!

So why map it at all? The only thing mapping it can do is to hide bugs.

			Linus
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