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

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Date:	Sun, 18 Jul 2010 11:22:49 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Avi Kivity <avi@...hat.com>
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 Sun, Jul 18, 2010 at 11:04 AM, Avi Kivity <avi@...hat.com> wrote:
>
> Too simple - an MCE will switch to its own stack, failing the test.  Now
> that we have correctable MCEs, that's not a good idea.

Ahh, true. And I think we do DEBUG traps with IST too.

So we do need the explicit flag over the region. Too bad. I was hoping
to handle the nested case without having to set up the percpu segment
(that whole conditional swapgs thing, which is extra painful in NMI).

And at that point, if you require the separate flag anyway, the %rsp
range test is equivalent to the %rip range test.

                Linus
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