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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On Mon, 4 Jun 2007, Eric W. Biederman wrote:

Jesse Barnes <[email protected]> writes:

On Friday, June 1, 2007 2:19:43 Andi Kleen wrote:
And normally the MTRRs win, don't they (if I remember the table correctly)
So if the MTRR says UC and PAT disagrees it might not actually help

I just checked, yes the MTRRs win for UC types.  But it sounds like the cases
we're talking about are actually situations where there's no MTRR coverage,
so the default type is used.  The manual doesn't specifically call out how
memory using the default type interacts with PAT, but it may well be that it
stays uncached if the default type is uncached.  Again that argues for fixing
the MTRR mapping problem in some way.

Last I looked PAT can only demote not promote the type of a page,
except for the specific exception of UC to WC.

Normally the default type is UC so putting a pat type of WB won't
help anything.  I may have missed some subtle detail but I remember
looking into this in some detail a while ago and coming to that
conclusion.

It is the BIOS's responsibility to mark all usable memory as WB,
using the MTRRs.  If it doesn't it is a BIOS bug.

Eric


According to Intel it is not a BIOS bug but rather the media controller
hub (MCH) uses memory for various purposes, outlined in their doc:

From their response, it sounds like the kernel needs to setup the memory
properly to deal with the MCH found in the 965 motherboards?

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:

Therefore, they are NOT going to fix their BIOS-- and I have already received an e-mail from one or two people who are experiencing this problem, I presume it will only get worse.

Justin.
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