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

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Message-ID: <20100715234821.GB25420@one.firstfloor.org>
Date:	Fri, 16 Jul 2010 01:48:21 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	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>,
	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 Thu, Jul 15, 2010 at 04:23:20PM -0700, Linus Torvalds wrote:
> On Thu, Jul 15, 2010 at 4:20 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > On 07/15/2010 03:58 PM, Andi Kleen wrote:
> >>> Why do we force IST use for NMI, btw? Maybe we shouldn't, and just use
> >>> the normal kernel stack mechanisms?
> >>
> >> If you don't use IST the SYSCALL entry is racy during the window
> >> when RSP is not set up yet (same for MCE etc.)
> >>
> >
> > Right, the kernel stack is not ready.
> 
> Well, it may not be ready for the _current_ NMI handler, but if we're
> going to do a stack switch in sw on NMI anyway... ?

The CPU written initial stack frame would still go on the wrong stack.

-Andi

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