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

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Message-ID: <4C40B57A.1090107@redhat.com>
Date:	Fri, 16 Jul 2010 22:39:38 +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 10:29 PM, H. Peter Anvin wrote:
> On 07/16/2010 11:32 AM, Avi Kivity wrote:
>    
>> How long would vmalloc_sync_all take with a few thousand mm_struct take?
>>
>> We share the pmds, yes?  So it's a few thousand memory accesses.  The
>> direct impact is probably negligible, compared to actually loading the
>> module from disk.  All we need is to make sure the locking doesn't slow
>> down unrelated stuff.
>>
>>      
> It's not the memory accesses, it's the need to synchronize all the CPUs.
>    

I'm missing something.  Why do we need to sync all cpus?  the 
vmalloc_sync_all() I'm reading doesn't.

Even if we do an on_each_cpu() somewhere, it isn't the end of the world.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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