Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn'tthe kernel realize the BIOS has problems and re-map appropriately?

[Justin Piszcz]

On Mon, 4 Jun 2007, Justin Piszcz wrote:

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