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

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Date:	Sat, 16 Oct 2010 20:36:57 +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 Sat, Oct 16, 2010 at 05:15:16PM +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.
> 
>   Maciej
> 

 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
 )

  Cyrill
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