Date: Wed, 14 Jul 2010 16:05:52 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Steven Rostedt <rostedt@rostedt.homelinux.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Christoph Hellwig <hch@lst.de>,
        Li Zefan <lizf@cn.fujitsu.com>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        Johannes Berg <johannes.berg@intel.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Tom Zanussi <tzanussi@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        "Frank Ch. Eigler" <fche@redhat.com>, Tejun Heo <htejun@gmail.com>
Subject: Re: [patch 1/2] x86_64 page fault NMI-safe
Message-ID: <20100714200552.GA22096@Krystal>
References: <20100714154923.947138065@efficios.com> <20100714155804.049012415@efficios.com> <AANLkTiml2uwYqQayTKjMN2gI3LnjVFpwxXkv8GN3McEE@mail.gmail.com> <20100714170617.GB4955@Krystal> <AANLkTinLB3gQNKFk9QRfBS8YEfxL3qxZDFw7vWHDOnmL@mail.gmail.com> <20100714184642.GA9728@elte.hu> <AANLkTil2r3sUcoCC_ktp3TV2JNTSMxbpke8yJMx_8lmm@mail.gmail.com> <AANLkTinfmoKvi1SauDA5_RiTmu6bztTDk8b_ycS-lr8S@mail.gmail.com> <20100714195617.GC22373@basil.fritz.box>
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* Andi Kleen (andi@firstfloor.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@linux.intel.com -- Speaking for myself only.

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