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: <Pine.LNX.4.64.0706041508040.27826@p34.internal.lan>
Date:	Mon, 4 Jun 2007 15:08:32 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	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, 4 Jun 2007, Justin Piszcz wrote:

>
>
> On Mon, 4 Jun 2007, Eric W. Biederman wrote:
>
>> Jesse Barnes <jbarnes@...tuousgeek.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.
>
> Justin.
>

Therefore, since they will NOT commit to a BIOS fix (they claim not a BIOS 
issue) what options does that leave us with?

Justin.
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