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Date: Thu, 15 Jul 2010 16:23:20 -0700
Message-ID: <AANLkTinLg2Xx0x6jrKkK_em6dA0cEfujnV3XIZ6I10jI@mail.gmail.com>
Subject: Re: [patch 1/2] x86_64 page fault NMI-safe
From: Linus Torvalds <torvalds@linux-foundation.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Steven Rostedt <rostedt@rostedt.homelinux.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Christoph Hellwig <hch@lst.de>,
        Li Zefan <lizf@cn.fujitsu.com>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        Johannes Berg <johannes.berg@intel.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Tom Zanussi <tzanussi@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        "Frank Ch. Eigler" <fche@redhat.com>, Tejun Heo <htejun@gmail.com>
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On Thu, Jul 15, 2010 at 4:20 PM, H. Peter Anvin <hpa@zytor.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... ?

                 Linus
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