linux-kernel - Re: [RFC] x86, NMI, Treat unknown NMI as hardware error

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Date:	Tue, 17 May 2011 10:50:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Don Zickus <dzickus@...hat.com>
Cc:	huang ying <huang.ying.caritas@...il.com>,
	Huang Ying <ying.huang@...el.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>,
	Andi Kleen <ak@...ux.intel.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC] x86, NMI, Treat unknown NMI as hardware error


* Don Zickus <dzickus@...hat.com> wrote:

> On Mon, May 16, 2011 at 01:29:34PM +0200, Ingo Molnar wrote:
> > > Interesting.  Question though, what do you mean by 'event filtering'.  Is 
> > > that different then setting 'unknown_nmi_panic' panic on the commandline or 
> > > procfs?
> > > 
> > > Or are you suggesting something like registering another callback on the 
> > > die_chain that looks for DIE_NMIUNKNOWN as the event, swallows them and 
> > > implements the policy?  That way only on HEST related platforms would 
> > > register them while others would keep the default of 'Dazed and confused' 
> > > messages?
> > 
> > The idea is that "event filters", which are an existing upstream feature and 
> > which can be used in rather flexible ways:
> > 
> >   http://lkml.org/lkml/2011/4/27/660
> > 
> > Could be used to trigger non-standard policy action as well - such as to panic 
> > the box.
> > 
> > This would replace various very limited /debugfs and /sys event filtering hacks 
> > (and hardcoded policies) such as arch/x86/kernel/cpu/mcheck/mce-severity.c, and 
> > it would allow nonstandard behavior like 'panic the box on unknown NMIs' as 
> > well.
> > 
> > This could be set by the RAS daemon, and it could be propagated to the kernel 
> > boot line as well, where event filter syntax would look like this:
> > 
> >   events=nmi::unknown"if (reason == 0) panic();"
> 
> Wow. ok.  I believe that is the most complicated kernel boot param I have
> ever seen. :-)  Powerful, no doubt.

It would not have to be typed normally - the defaults would still be sane.

> So this would sorta be a meta-notifier?  I guess you are saying platforms 
> that implement something like HEST could setup an event like that to trigger 
> the behaviour they want on a per-platform basis?

Yeah - or if they dislike the default they could tweak the policy action in a 
rather flexible way.

> My only argument against it would be sorta of what Ying complains about is 
> that you start to lose track of who is hooked into the NMI.  It is one thing 
> to search for all the users in the die_notifier to track down who is 
> swallowing NMIs.  But to look for event users, is going to be harder. Unless 
> the events processing has a switch to turn on logging? :-)

Yeah, all such types of filters should be printed during bootup, to make it 
really clear what is happening.

We also want all the current state visible readily under /sys/events or 
/events.

Thanks,

	Ingo
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