linux-kernel - Re: [PATCH] x86: fixed mtrr change WP to WB

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Date:	Tue, 06 May 2008 11:31:29 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: fixed mtrr change WP to WB

Yinghai Lu wrote:
>>
>>  If the mptable should be modified, it should be copied to kernel memory and
>> modified there.  Modifying it in-place is both unsafe and, in general,
>> simply will not work.
> 
> but
> 
>          * 1) Scan the bottom 1K for a signature
>          * 2) Scan the top 1K of base RAM
>          * 3) Scan the 64K of bios
>          */
>         if (smp_scan_config(0x0, 0x400, reserve) ||
>             smp_scan_config(639 * 0x400, 0x400, reserve) ||
>             smp_scan_config(0xF0000, 0x10000, reserve))
>                 return;
> 
> and all these areas are reserved already.
> 
> wonder if we could only modify mpf->mpf_physptr to point to another
> mpc and reuse mpf?
> 

Obviously, if you have already modified a table, you should save a 
pointer to it, and not rely on the kernel scanning later.

	-hpa
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