Subject: Re: visible memory seems wrong in kexec crash dump kernel

From: Chris Friesen <[email-masked]>
Date: Thu, 11 Jul 2013 16:46:16 -0600

On 07/11/2013 03:22 PM, Chris Friesen wrote:
> On 07/11/2013 02:55 PM, Chris Friesen wrote:
>> Hi,
>>
>> I'm running 2.6.34 with kexec 2.0.1 on a Freescale p5020-based system
>> with 8GB of memory. (It's an embedded system and I can't do much
>> about the fact that it's using older software.)
>
> I should probably clarify this...I may be able to update kexec, I can't
> update the kernel but I can backport more recent code if necessary.
>
> Looking at the version of kexec that I have, it seems like where x86
> uses "memmap=" to specify the memory map usable by the capture kernel,
> powerpc does something different.

After some experimenting, it looks like in the capture kernel 
/dev/oldmem might actually refer to the memory owned by the old kernel.

However, there doesn't seem to be anything preventing me from trampling 
it from within the capture kernel--I can create a tmpfs filesystem in 
memory and write gigs of data to it even though the capture kernel is 
only supposed to have 224MB.

I think I got it to work properly once, but since then I haven't been 
able to get uncorrupted data out of /dev/oldmem.  (My original kernel 
reserves a chunk of memory for logging and passes the offset/size to the 
capture kernel via kexec kernel args.)

Chris