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 Fri, 1 Jun 2007, Jesse Barnes wrote:

> 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

Indeed, at least it will inform the user of -what- is going on.
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