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

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Date:	Fri, 16 Jul 2010 14:22:40 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.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>, akpm@...l.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

* Avi Kivity (avi@...hat.com) wrote:
> On 07/16/2010 09:05 PM, H. Peter Anvin wrote:
>>
>>> Module loading can certainly take a vmalloc_sync_all() (though I agree
>>> it's unpleasant).  Anything else?
>>>
>>> Note perf is not modular at this time, but could be made so with
>>> preempt/sched notifiers to hook the context switch.
>>>
>>>      
>> Actually, module loading is already a performance problem; a lot of
>> distros load sometimes hundreds of modules on startup, and it's heavily
>> serialized, so I can see this being desirable to skip.
>>    
>
> There aren't that many processes at this time (or there shouldn't be,  
> don't know how fork-happy udev is at this stage), so the sync should be  
> pretty fast.  In any case, we can sync only modules that contain NMI  
> handlers.

USB hotplug is a use-case happening randomly after the system is well there and
running; I'm afraid this does not fit in your module loading expectations. It
triggers tons of events, many of these actually load modules.

Thanks,

Mathieu

>
>> I really hope noone ever gets the idea of touching user space from an
>> NMI handler, though, and expecting it to work...
>>    
>
> I think the concern here is about an NMI handler's code running in  
> vmalloc space, or is it something else?
>
> -- 
> I have a truly marvellous patch that fixes the bug which this
> signature is too narrow to contain.
>

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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