[Jeff Garzik <address@hidden>] Re: ack! grub bug...

[Pixel]

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From: Jeff Garzik <address@hidden>
To: Pixel <address@hidden>
cc: MandrakeSoft Internal <address@hidden>
Subject: Re: ack! grub bug...
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On Wed, 21 Feb 2001, Pixel wrote:
> Jeff Garzik <address@hidden> writes:
> > Ok...  Phillip and I just finished debugging a kernel problem that
> > wasn't a kernel problem.  :)
> > 
> > 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.


> > For kernel 2.4, this is -bad- and -wrong-.
> 
> why? 

It completely overrides the BIOS memory map with a standard memory map
containing two sections:  one for memory before 640k, and one for memory
after 1MB.

Newer machines have several regions of reserved memory outside and
inside these regions.  grub's actions are suicide on newer laptops,
and machines like servers with lots of memory.  Laptops have special
sections of memory above 1MB which must be reserved... Ditto for
ACPI tables.  Using mem=XXX completely eliminates any information
that the BIOS has provided to the OS.

The Dells here in the office, in fact, have a special region
of reserved address space that is dedicated to the Random Number
Generator (RNG) and other devices attached to the Intel Firmware Hub.
This hardware-special region is no longer reserved, when booting with
grub.  That means the kernel might try to address it directly, if you
have enough memory:  boom, crash!

Grub cannot do this on kernel 2.4, and probably should not do it on
kernel 2.2.  I must check for kernel 2.2... I think the 2.2 bug is
fixed.  Definitely not for 2.4.  It makes the kernel unstable to do so.

        Jeff




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