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

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Date:	Sat, 4 Oct 2008 18:49:46 -0700
From:	"Yinghai Lu" <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.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

On Sat, Oct 4, 2008 at 5:46 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.

so it is safe to put it in WB, and can be spare some regs because it
start from base 0.

>
> 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..

YH
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