makedumpfile bug with ppc64 CONFIG_SPARSEMEM_EXTREME

[Dave Anderson]

----- Original Message -----
> 
> Our QA group recently ran into a makedumpfile problem while
> testing kdump/makedumpfile w/upstream 3.7.1 kernels, which
> had to do with the filtering of pages on a 12GB ppc64 system.
>
... [ cut ] ...
> 
> I haven't checked why the original math fails in the case of the
> ppc64 kernel, while it does not fail in a CONFIG_SPARSEMEM_EXTREME
> x86_64 kernel, for example. (page size maybe?)  But obviously the
> simpler dimemsion-check is a better way to do it.
> 
> Of course, within the current constraints of makedumpfile, it's not
> that easy.  Ideally the kernel could pass the configuration in
> the vmcoreinfo with a VMCOREINFO_CONFIG(name).  But anyway, I'll leave
> that up to you.
> 
> Thanks,
>   Dave

It's presumably being seen in 3.7.1 because of this commit:

  $ git log -p arch/powerpc/include/asm/sparsemem.h
  commit 048ee0993ec8360abb0b51bdf8f8721e9ed62ec4
  Author: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
  Date:   Mon Sep 10 02:52:55 2012 +0000

      powerpc/mm: Add 64TB support
    
      Increase max addressable range to 64TB. This is not tested on
      real hardware yet.
    
      Reviewed-by: Paul Mackerras <paulus at samba.org>
      Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
      Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

  diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
  index 0c5fa31..f6fc0ee 100644
  --- a/arch/powerpc/include/asm/sparsemem.h
  +++ b/arch/powerpc/include/asm/sparsemem.h
  @@ -10,8 +10,8 @@
    */
   #define SECTION_SIZE_BITS       24
 
  -#define MAX_PHYSADDR_BITS       44
  -#define MAX_PHYSMEM_BITS        44
  +#define MAX_PHYSADDR_BITS       46
  +#define MAX_PHYSMEM_BITS        46
 
   #endif /* CONFIG_SPARSEMEM */

  $ git describe --contains 048ee0993ec8360abb0b51bdf8f8721e9ed62ec4
  v3.7-rc1~108^2~32
  $
  
Dave