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

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Message-ID: <4C42C81B.20301@redhat.com>
Date:	Sun, 18 Jul 2010 12:23:39 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 07/17/2010 12:39 AM, Linus Torvalds wrote:
> 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.
>    

Well, I'd put it in the nmi handler registration code, but you're 
right.  A user placing breakpoints can't even tell whether the 
breakpoint will be hit by NMI code, especially data breakpoints.

> 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.
>    

Well, at least we'll get a good test case for kvm's nmi blocking 
emulation (it's tricky since if we fault on an iret sometimes nmis get 
unblocked even though the instruction did not complete).

-- 
error compiling committee.c: too many arguments to function

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