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

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Date:	Thu, 10 Jan 2008 20:06:53 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	venkatesh.pallipadi@...el.com
Cc:	ebiederm@...ssion.com, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie,
	davej@...hat.com, mingo@...e.hu, tglx@...utronix.de, hpa@...or.co,
	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

venkatesh.pallipadi@...el.com writes:

> x86_64: Map only usable memory in identity map. 

I don't think that is needed or makes sense for reserved/ACPI * etc. 
Only e820 holes should be truly unmapped because only those should
contain mmio.

> All reserved memory maps to a
> zero page. 

Why zero page?  Why not unmap.

Anyways you could make that a zillion times more simple by just rounding
the e820 areas to 2MB -- for the holes only that should be ok I think; 
i would expect them to be near always already suitably aligned.

In short this can be all done much simpler.

-Andi
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