linux-kernel - Re: [Patch 1/4][kernel][slimdump] Add new elf-note of type NT

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Date:	Wed, 5 Oct 2011 11:40:11 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, crash-utility@...hat.com,
	kexec@...ts.infradead.org, Andi Kleen <andi@...stfloor.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, anderson@...hat.com,
	tachibana@....nes.nec.co.jp, oomichi@....nes.nec.co.jp,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [Patch 1/4][kernel][slimdump] Add new elf-note of type
 NT_NOCOREDUMP to capture slimdump

On Wed, Oct 05, 2011 at 01:11:16PM +0530, K.Prasad wrote:

[..]
> > Again, note_name and desc_msg seem to be only two exports. Frankly desc
> > string seems pretty obivious and we should be able to ignore it. So just
> > exporting PANIC_MCE=true or something like that in case of MCE. 
> >
> 
> Yes, adding a new field to the VMCOREINFO note would have been much
> simpler but there's a second part to the kdump + fatal MCE problem which
> will need a new elf-note to solve.
> 
> On a system containing 'poisoned' pages (generated as a result of
> detecting UC errors which haven't been 'consumed'), if a software bug results
> in crashing the machine, the ensuing kdump operation will read from the
> faulty memory location. This will trigger a new crash within the context
> of the kexec'ed kernel and we want to avoid this.

I think in other mail you mentioned that it is not known what happens
if we try to read pages marked as "poisoned".

> 
> The plan is to pass-down the list of poisoned memory pages to the second
> kernel using an elf-note so that these pages are left untouched during
> dump capture. I'm working on an implementation of the same and should
> have patches soon.

I would say let us first figure out what happens while reading a poisoned
page and is this a problem before working on a solution.

Thanks
Vivek
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