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Re: ack! grub bug...


From: Jeff Garzik
Subject: Re: ack! grub bug...
Date: Thu, 22 Feb 2001 01:15:00 -0600 (CST)

On Wed, 21 Feb 2001, Pavel Roskin wrote:
> > > > grub -always- passes the "mem=XXX" command line option to the kernel.
> > >
> > > it's always been that way...
> >
> > It works around a kernel bug.  That is wrong in and of itself.
> > A kernel bug fix belongs in the kernel, not in grub.
> 
> I remember a discussion on this topic, and the argument for "mem=" was
> that GRUB knows something about the system and uses the standard
> mechanism to share this information with the kernel.
> 
> It's up to the kernel to decide what to do with this information.

mem=XXX overrides the memory map provided by BIOS with a two-region
memory map, one region below 640k, and one region above 1MB.

For newer machines this is -fatally- wrong.  Linux must use the memory
map provided by BIOS, otherwise it will address regions which should not
be addressed.  Newer laptops and server machines require utilization of
the BIOS e820 map.

Even if the memory detection it wrong (which we've seen no bug reports
of in quite a while), the user must provide their own memory map to the
kernel on the command line.  mem=XXX is not sufficient memory map.

This feature has got-to-go for 2.4 kernels.  I -believe- that the memory
detection problems have been fixed in 2.2 kernels for at least six
months, but I still need to verify this.

        Jeff







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