linux-kernel - Re: [PATCH] x86: disable_mtrr_trim only need for x86

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Date:	Sat, 19 Jan 2008 22:55:25 -0800
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Andi Kleen" <ak@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Jesse Barnes" <jesse.barnes@...el.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86: disable_mtrr_trim only need for x86_64

On Jan 19, 2008 9:37 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Yinghai Lu wrote:
> > [PATCH] x86: disable_mtrr_trim only need for x86_64
> >
> > mtrr_trim_uncached_memory is only used in x86_64,
> >
> > so disable_mtrr_trim is not needed for x86_32
> >
> > Signed-off-by: Yinghai Lu <yinghai.lu@....com>
>
> That seems like a bug, and if so this patch goes the wrong direction.
> (If the 32-bit code has another solution for the same problem, they
> should be unified.)
>
> The trimming of uncachable memory affects both 32- and 64-bit kernels;
> it's the same hardware, and even 32-bit kernels (with PAE) can access
> memory above 4 GB.
>

the trim fix for x86_64 is update end_pfn, and use that as max_pfn,
and max_low_pfn in setup_arch.

but i386 is setup_arch is only using max_low_pfn.

to make you happy, the simple way is update e820 table so code could
be unified between i386 and x86_64

update the e820 table by checking mtrr like checking gart hole...

is that OK?

YH
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