linux-kernel - Re: [PATCH 2/3] x86: mtrr_cleanup: first 1M should be coverred in var mtrrs

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Date:	Sat, 04 Oct 2008 18:52:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: mtrr_cleanup: first 1M should be coverred in
 var mtrrs

Yinghai Lu wrote:
>> The first 1 MB is a total don't care for the variable MTRRs -- they don't
>> have to be covered *or* uncovered, since the entire first 1 MB is addressed
>> by fixed MTRRs.
> 
> so it is safe to put it in WB, and can be spare some regs because it
> start from base 0.

Yes, my point was that you can make those whatever you want.  It doesn't 
have to be WB; it can be any value.

>> In practice, it is *likely* that you're going to want to merge it with a WB
>> MTRR, but with various vendors doing all kinds of strange things on
>> EFI-damaged platforms, it may not always be that way.
> 
> EFI will not use fixed-mtrr for first 1M? and not cover first 1M in
> var mtrr with WB? that will run out mtrr regs..

There are some systems which, apparently, don't have RAM there.  Don't 
ask me how or why.

	-hpa
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