linux-kernel - Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately?

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Message-ID: <20070607084711.GB15226@one.firstfloor.org>
Date:	Thu, 7 Jun 2007 10:47:11 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately?

On Mon, Jun 04, 2007 at 05:59:59PM -0700, Yinghai Lu wrote:
> On 6/4/07, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >
> >Exactly, and given that this is a fairly easy thing to do, and that
> >occasionally we see systems where this happens (even if their BIOS is
> >later fixed).  It is likely worth it for someone to write up the patch
> >and that compare MTRRs with available memory, and to complain and
> >reserve all memory that MTRRs claim is not write-back.
> >
> that is good.
> Sometime BIOS can not even keep mtrr to the identical between
> different CPU in SMP system.

The MTRR code already fixes this case. Or at least mostly -- 
it doesn't do it for fixed size MTRRs.

> Or reset mtrr according to e820 table.

That would be likely dangerous.

-Andi
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