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: <200706011815.53065.jbarnes@virtuousgeek.org>
Date:	Fri, 1 Jun 2007 18:15:52 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Venki Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	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 Friday, June 1, 2007 6:05:39 Venki Pallipadi wrote:
> On Fri, Jun 01, 2007 at 02:41:57PM -0700, Jesse Barnes wrote:
> > 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.
>
> I feel, having a silent/transparent workaround is not a good idea. With
> that chances are BIOS bug will go unnoticed (having an error message in
> dmesg may not get noticed either). Probably we should just panic at boot
> with a
> detailed message about the e820 mtrr discrepancy (which can be logged as
> a BUG to BIOS provider) and suggest a temporary workaround of "mem=___".

That might be best, short of actually fixing the MTRRs...

Jesse


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