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SubjectRe: 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@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.
>
> 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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