linux-kernel - Re: [patch 0/9] kdump: Patch series for s390 support

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Date:	Wed, 13 Jul 2011 18:59:50 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, ebiederm@...ssion.com,
	hbabu@...ibm.com, mahesh@...ux.vnet.ibm.com,
	oomichi@....nes.nec.co.jp, horms@...ge.net.au,
	heiko.carstens@...ibm.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [patch 0/9] kdump: Patch series for s390 support

On Wed, 2011-07-13 at 18:46 +0200, Martin Schwidefsky wrote:
> On Wed, 13 Jul 2011 12:02:39 -0400
> Vivek Goyal <vgoyal@...hat.com> wrote:
> > So in case of stand alone dump, you save the calculated checksum of
> > kdump kernel at disk and not in memory? And then calculate the checksum
> > of memory image of kdump kernel and decide whether kdump kenrel is 
> > corrupted or not?
> > 
> > If yes, this sounds more reliable as checksum of kernel is stored on
> > some disk/tape.
> 
> No, the checksum for the purgatory code is stored in memory. If the purgatory
> code is corrupted you would have to corrupt the checksum in a very specific
> way as well to make it fail. 

Currently we store the checksums for the loaded *kexec segments* in
memory at the end of kexec_load(). The stand-alone dump tools also
calculate the checksums for all segments and compare them with the
stored checksums. The dump tools can do that because we have meminfos
for all segments. A meminfo element contains:
* address of memory chunk
* size of memory chunk
* checksum of memory chunk (calculated at the end of kexec_load()

Michael

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