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

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Message-ID: <alpine.LFD.2.00.1007142313460.11778@eddie.linux-mips.org>
Date:	Wed, 14 Jul 2010 23:31:10 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.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>,
	"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

On Wed, 14 Jul 2010, Linus Torvalds wrote:

> You just count differently. I don't count the first one (the "real"
> NMI). That obviously happens. So I only count how many interrupts we
> need to fake. That's my "one". That's the one that happens as a result
> of the fault that we take on the iret in the emulated model.

 Ah, I see -- so we are on the same page after all.

> (Yeah, yeah, you can call it a "one-bit counter", but I don't think
> that's a counter. It's just a bit of information).

 Hardware has something like a strapped-high D flip-flop (NMI goes to the 
clock input) with an extra reset input I presume -- this dates back to 
8086 when the transistor count mattered with accuracy higher than 1e6. ;)

  Maciej
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