Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately?

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Mon, 4 Jun 2007, Ray Lee wrote:

> On 6/4/07, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > 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.
>
> Ick. Systems that used to boot fine would then panic on a kernel
> upgrade. That's rather rude for a condition that's merely an
> optimization (using all memory), rather than one of correctness. A
> panic seems entirely inappropriate.
>
> Ray

While I am unsure of the 'best' solution, if they boot and it does not 
panic but takes 10 minutes to boot, people are going to seriously wonder 
what is going on?

Justin.
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