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From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Matt Keenan <tank.en.mate@gmail.com>
Subject: Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately?
Date: Mon, 4 Jun 2007 08:40:21 -0700
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Cc: Justin Piszcz <jpiszcz@lucidpixels.com>, Andi Kleen <andi@firstfloor.org>,
       Venki Pallipadi <venkatesh.pallipadi@intel.com>,
       linux-kernel@vger.kernel.org
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On Sunday, June 3, 2007 2:15:06 Matt Keenan wrote:
> Justin Piszcz wrote:
> > On Sat, 2 Jun 2007, Andi Kleen wrote:
> >>> I feel, having a silent/transparent workaround is not a good idea.
> >>> With that
> >>
> >> If enough RAM is chopped off users will notice. They tend to complain
> >> when they miss RAM.  I don't like panic very much because for many
> >> users it will be a show stopper (even when they are not blessed
> >> with "quiet" boots like some distributions do)
> >>
> >> The message in dmesg could be also emphasized a bit with a little
> >> ASCII art (but no <blink> tag in there)
> >>
> >> The problem I'm more worried about is if the system will be really
> >> stable --- could it be that the memory controller is still
> >> misconfigured and cause other stability issues? (we've had such
> >> cases in the past). Also I'm not sure we can handle the case of
> >> the MTRR wrong not at the end of memory but at the hole sanely.
> >>
> >> -Andi
> >
> > So far I have been booting with mem=8832M and have run stress/loaded
> > the memory subsystem pretty good; what other tests should I run?
> >
> > It'd be nice if we could pose some sort of solution/warning for the
> > future so other people do not have to experience the same problems.
> >
> > What are the next steps?
>
> Wouldn't it be possible for the e820/MTRR set up code detect the problem
> and suggest a mem=xxxx that would fix the problem (while also
> complaining that the BIOS is broken)?

Yes, that should be fairly easy, though as Andi points out, if there are holes 
in the MTRR setup, things get a little trickier (I had an earlier patch to 
deal with this, but ended up with too many early boot issues).

Maybe what Venki suggested would be best:  just detect the condition and 
panic, with a string telling the user to use mem=xxx (we can figure that out) 
and/or upgrade their BIOS.

I'll spin a new patch to do that today.

Jesse
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