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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Date:	Mon, 4 Jun 2007 17:54:46 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Justin Piszcz" <jpiszcz@...idpixels.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Jesse Barnes" <jbarnes@...tuousgeek.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 6/4/07, Andi Kleen <andi@...stfloor.org> wrote:
> > From their e-mail:
> >
> > Note before continuing: Debian* Linux Operating System is not an
> > officially, validated, tested Operating System for the Intel(R) Desktop
> > Board DG965WH
> > (see http://downloadcenter.intel.com/Product_Filter.aspx?ProductID=2375);
> > moreover, we do confirm that "on a system that has 8 GB of system memory
> > installed, it is not possible to use all of the installed memory due to
> > system address space being allocated for other system critical functions."
> > [qtd. on page 43 of the Technical Product Specification (see
> > http://download.intel.com/design/motherbd/wh/D5600801US.pdf)].  Thus, the
> > following suggestions are provided AS IS; we cannot guarantee the problem
> > would be fixed afterwards:
>
> They're talking about something different than your issue. If you put in
> the fully possible 8GB (4x2GB) then some memory will be lost to the PCI hole
> because the desktop ICH can only access 35bits (8GB) in hardware.
>
> That can be up to 2GB in extreme cases, usually <0.5-1GB depending
> on how much mapping space your hardware needs.
>
> But if you put in less than 8GB the BIOS is supposed to remap
> the memory around the PCI hole and set up the MTRRs correctly
> so that the PCI hole is uncached and the memory around it is cached.
>
> That is 100% the BIOS' responsibility and if it doesn't do that
> it is buggy.

then the BIOS need to disable mem remap to make thing simple if there
8G ram installed.

YH
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