On Wed, Apr 05, 2006 at 09:28:18PM +0200, Takashi Iwai wrote:
> Hi,
> 
> I've got a bug report of SLES10-beta about non-working kdump on
> a x86-64 machine.  It seems because of the ACPI tables overlapping the
> default [EMAIL PROTECTED] crash region:
> 
>       % cat /proc/iomem
>       ....
>       0100000-0266ffff : System RAM
>         00100000-002d32a3 : Kernel code
>         002d32a4-003ac0f7 : Kernel data
>       02670000-026d5fff : ACPI Tables
>       026d6000-026fffff : ACPI Non-volatile Storage
>       02700000-efffffff : System RAM
>       ...
> 


That's interesting. I always assumed that 16MB to 80MB can be safely 
reserved. Generally I have seen that ACPI tables are mapped at high
addresses. 

> The crash region itself can be changed via boot option to another
> offset.  But kexec refuses to load since the address doesn't match
> with the pre-built kdump kernel using PHYS_START=16M.

Here is another reason for having relocatable kernel. 

> 
> What would be a workaround for such a problem?
> It seems that the ACPI location cannot be changed easily, and we don't
> want to rebuild a kernel as much as possible just for a single
> case...

Roughly first 3.7 MB is being used by first kernel's code and data. You
can try resrving memory from 5MB to 38MB ([EMAIL PROTECTED]) and see
if second kernel is able to boot in 32MB of memory. Kexec should still be
able to load the second kernel as 16MB is within reserved region.

-vivek
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