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

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Message-ID: <4C43FF73.1070305@redhat.com>
Date:	Mon, 19 Jul 2010 10:32:03 +0300
From:	Avi Kivity <avi@...hat.com>
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 07/18/2010 09:22 PM, Linus Torvalds wrote:
> 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).
>    

Well, we have to do that anyway for the non-nested case.  So we just do 
it before checking whether we're nested or not, and undo it on the popf; 
retf path.

-- 
error compiling committee.c: too many arguments to function

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