Messages in this thread | | | Date | Mon, 4 Jun 2007 14:22:05 -0400 (EDT) | From | Justin Piszcz <> | Subject | 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 <jbarnes@virtuousgeek.org> 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.
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