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

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Message-ID: <86802c440805061124w630bc987k71c3c290fdfde773@mail.gmail.com>
Date:	Tue, 6 May 2008 11:24:11 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"H. Peter Anvin" <hpa@...or.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

On Tue, May 6, 2008 at 10:48 AM, H. Peter Anvin <hpa@...or.com> wrote:
> Yinghai Lu wrote:
>
> > [PATCH] x86: fixed mtrr change WP to WB
> >
> > so we modify mptable near below 1M
> >
> > Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
> >
>
>  Again:
>
>  This does not work on even the majority of all systems.
>
>  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?

YH
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