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

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Message-ID: <20100716193406.GF7338@basil.fritz.box>
Date:	Fri, 16 Jul 2010 21:34:06 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, "H. Peter Anvin" <hpa@...or.com>,
	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>,
	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 Fri, Jul 16, 2010 at 10:32:13PM +0300, Avi Kivity wrote:
> On 07/16/2010 10:28 PM, Andi Kleen wrote:
> >
> >>I really hope noone ever gets the idea of touching user space from an
> >>NMI handler, though, and expecting it to work...
> >It can make sense for a backtrace in a profiler.
> >
> >In fact perf is nearly doing it I believe, but moves
> >it to the self IPI handler in most cases.
> 
> Interesting, is the self IPI guaranteed to execute synchronously
> after the NMI's IRET?  Or can the core IRET faster than the APIC and
> so we get the backtrace at the wrong place?
> 
> (and does it matter? the NMI itself is not always accurate)

self ipi runs after the next STI (or POPF)

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