linux-kernel - Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

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Date:	Fri, 16 Jul 2010 11:25:19 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <rostedt@...tedt.homelinux.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>, Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

On Fri, Jul 16, 2010 at 11:15 AM, Avi Kivity <avi@...hat.com> wrote:
>
> I think the concern here is about an NMI handler's code running in vmalloc
> space, or is it something else?

I think the concern was also potentially doing things like backtraces
etc that may need access to the module data structures (I think the
ELF headers end up all being in vmalloc space too, for example).

The whole debugging thing is also an issue. Now, I obviously am not a
big fan of remote debuggers, but everybody tells me I'm wrong. And
putting a breakpoint on NMI is certainly not insane if you are doing
debugging in the first place. So it's not necessarily always about the
page faults.

                               Linus
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