linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <CALCETrXmJhp79j4va-=U9v_aSp3vvtz0Zzuz_PfM_bz=sL98vg@mail.gmail.com>
Date:	Thu, 23 Jul 2015 14:46:26 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Willy Tarreau <w@....eu>, Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Dealing with the NMI mess

On Thu, Jul 23, 2015 at 2:20 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 23 Jul 2015 13:21:16 -0700
> Andy Lutomirski <luto@...capital.net> wrote:
>
>> 3. Forbid faults (other than MCE) inside NMI.
>>
>> Option 3 is almost easy.  There are really only two kinds of faults
>> that can legitimately nest inside NMI: #PF and #DB.  #DB is easy to
>> fix (e.g. with my patches or Peter's patches).
>
> What about int3? Which is needed to make ftrace work. This was a
> requirement to get rid of stomp-machine when updating ftrace functions,
> as well as the rational for doing the whole NMI nesting work in the
> first place.

OK, I'm convinced.

So I'll keep working on fixing up int3 to be less magical.  Patches
coming eventually.

--Andy
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