linux-kernel - Re: [patch 1/2] x86_64 page fault NMI-safe

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Message-ID: <20100714200552.GA22096@Krystal>
Date:	Wed, 14 Jul 2010 16:05:52 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Tejun Heo <htejun@...il.com>
Subject: Re: [patch 1/2] x86_64 page fault NMI-safe

* Andi Kleen (andi@...stfloor.org) wrote:
> > or similar. Wouldn't that be nice to have as a capability?
> 
> It means the NMI watchdog would get useless if these areas
> become common.
> 
> Again I suspect all of this is not really needed anyways if 
> vmalloc_sync_all() works properly. That would solve the original
> problem Mathieu was trying to solve for per_cpu data. The rule
> would be just to call vmalloc_sync_all() properly when changing
> per CPU data too.

Yep, that would solve the page fault in nmi problem altogether without adding
complexity.

> 
> In fact I'm pretty sure it worked originally. Perhaps it regressed?

I'd first ask the obvious to Perf authors: does perf issue vmalloc_sync_all()
between percpu data allocation and tracing activation ? The generic ring buffer
library I posted last week does it already as a precaution for this very
specific reason (making sure NMIs never trigger page faults).

Thanks,

Mathieu

> 
> -Andi
> -- 
> ak@...ux.intel.com -- Speaking for myself only.

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