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

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Date:	Sun, 18 Jul 2010 12:26:59 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	rostedt@...dmis.org
Cc:	Avi Kivity <avi@...hat.com>,
	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@...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 Sun, Jul 18, 2010 at 11:43 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Are you sure you don't want to use Mathieu's 2/2 patch?

Yeah, I'm pretty sure. Unless somebody can show that it's faster, I
really don't want to muck with regular iret's. Also, as shown during
the discussion, even with Mathieu's 2/2 patch, we'd _still_ need NMI
to also save cr2 etc.

So the sane thing to do is to put all the NMI crap where it belongs.
NMI's need to know about the fact that them taking exceptions is
special. That whole "vmalloc_sync_all()" is simply pure brokenness.

In other words, it is _not_ just about 'iret' fixup. It's a bigger
thing. NMI's are special, and we don't want to spread that specialness
around.

                  Linus
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