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Date: Tue, 06 May 2008 11:31:29 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Yinghai Lu <yhlu.kernel@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>, "Eric W. Biederman" <ebiederm@xmission.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: fixed mtrr change WP to WB
References: <200805041823.57198.yhlu.kernel@gmail.com>	 <200805061038.58023.yhlu.kernel@gmail.com>	 <200805061041.40047.yhlu.kernel@gmail.com>	 <482099E6.5060208@zytor.com> <86802c440805061124w630bc987k71c3c290fdfde773@mail.gmail.com>
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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