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

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Message-ID: <4C40A1BD.4040507@redhat.com>
Date:	Fri, 16 Jul 2010 21:15:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.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

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.

> 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.

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