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

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Message-ID: <48E80E60.8080106@zytor.com>
Date:	Sat, 04 Oct 2008 17:46:24 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
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:
> +	/*
> +	 * [0, 1M) should always be coverred by var mtrr with WB
> +	 * and fixed mtrrs should take effective before var mtrr for it
> +	 */
> +	nr_range = add_range_with_merge(range, nr_range, 0,
> +					(1ULL<<(20 - PAGE_SHIFT)) - 1);
> +	/* sort the ranges */
> +	sort(range, nr_range, sizeof(struct res_range), cmp_range, NULL);
> +

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.

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.

	-hpa
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