linux-kernel - Re: [RFC PATCH 0/4 V2] introduce: livedump

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Message-ID: <1337937942.9783.170.camel@laptop>
Date:	Fri, 25 May 2012 11:25:42 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	YOSHIDA Masanori <masanori.yoshida.tv@...achi.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@....edu>, Ingo Molnar <mingo@...e.hu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>,
	Kevin Hilman <khilman@...com>,
	Prarit Bhargava <prarit@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH 0/4 V2] introduce: livedump

On Fri, 2012-05-25 at 18:12 +0900, YOSHIDA Masanori wrote:
> Live Dump is based on Copy-on-write technique. Basically processing is
> performed in the following order.
> (1) Suspends processing of all CPUs.
> (2) Makes pages (which you want to dump) read-only.
> (3) Resumes all CPUs
> (4) On page fault, dumps a page including a fault address.

Suppose a PF is in progress when all this happens, you mark all RO, then
an NMI happens, from the NMI context we'll generate another PF to update
a vmap area, this will again PF because you mucked about and marked
things RO.

You're now at 3 PFs, which is instant reboot.

I don't think this is going to work.

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