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

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Message-ID: <AANLkTimfZb22E7c_ftyc5WfKsGvJKKq-J3Vq8Y6FNvhT@mail.gmail.com>
Date:	Fri, 16 Jul 2010 14:39:50 -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 12:26 PM, Avi Kivity <avi@...hat.com> wrote:
> On 07/16/2010 09:37 PM, Linus Torvalds wrote:
>>
>> Non-NMI code should simply never have to even _think_ about NMI's. Why
>> should it? It should just do whatever comes "natural" within its own
>> context.
>
> But we're not talking about non-NMI code.

Yes, we are. We're talking about breakpoints (look at the subject
line), and you are very much talking about things like that _idiotic_
vmalloc_sync_all() by module loading code etc etc.

Every _single_ "solution" I have seen - apart from my suggestion - has
been about making code "special" because some other code might run in
an NMI. Module init sequences having to do idiotic things just because
they have data structures that might get accessed by NMI.

And the thing is, if we just do NMI's correctly, and allow nesting,
ALL THOSE PROBLEMS GO AWAY. And there is no reason what-so-ever to do
stupid things elsewhere.

In other words, why the hell are you arguing? Help Mathieu write the
low-level NMI handler right, and remove that idiotic
"vmalloc_sync_all()" that is fundamentally broken and should not
exist. Rather than talk about adding more of that kind of crap.

                   Linus
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