linux-kernel - Re: [RFC] arch generic way to trigger unknown NMIs

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Message-ID: <20101017085828.GA7925@lenovo>
Date:	Sun, 17 Oct 2010 12:58:28 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Don Zickus <dzickus@...hat.com>, Andi Kleen <andi@...stfloor.org>,
	mingo@...e.hu, fweisbec@...il.com, robert.richter@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] arch generic way to trigger unknown NMIs

On Sun, Oct 17, 2010 at 12:59:11AM +0100, Maciej W. Rozycki wrote:
> On Sat, 16 Oct 2010, Cyrill Gorcunov wrote:
> 
> > > >  Hi Maciej, the send_IPI_self could be modified to send NMI (at moment it
> > > > uses self shortcut with fixed delivery mode). The question is rather if
> > > > we need it without a real caller yet. When Don's patch gets merged we
> > > > will have a real caller then and could update send_IPI_self to support
> > > > NMI delivery mode. Something like that :)
> > > 
> > >  Sounds backwards to me.  My understanding is a need has just arisen, so 
> > > why not:
> > > 
> > > 1. Update send_IPI_self().
> > > 
> > > 2. Add code that makes use of the new functionality.
> > > 
> > > 3. Submit all the changes as self-contained patches in a single series to 
> > >    be applied at the same time.
> > > 
> > > ?  That's what I'd imagine the most natural way of doing this would be.
> > 
> >  Well, Maciej I believe the problem is not in modifying send_IPI_self
> > but rather _how_ to make it more natural and do not introduce overhead.
> > apic code is already weird enough :) Need to think.
> > 
> > (
> >  btw, we will have to add additional flag which would check for NMI
> >  being generated by "NMI-tester" and make a second apic write to
> >  ICR to deassert level line, ie it could be something like
> > 
> >   apic->send_IPI_self(NMI_VECTOR)       ; with asserts level
> >    default_do_nmi()                     ; check for NMI being sent for testing purpose
> >      apic->send_IPI_self(NMI_VECTOR)    ; with deasserts level
> > 
> >  iirc apic itself doesn't deassert nmi line on message with
> >  nmi deliver mode arrival
> >  )
> 
>  How different is it to the other two send_IPI shorthand calls?  Or the 
> fully-fledged one?  I gather from this thread they already handle NMIs 
> properly, so what is there within that cannot simply be copied over to 
> this one?
> 
>   Maciej
> 

 Hmm, good question ;) I thought about 82489dx which required level
trigger mode for nmi delivery, new (or present day) apics always
use edge trigger mode so indeed there is no need for level assert/deassert.

  Cyrill
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