linux-kernel - Re: [V4][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs

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Message-ID: <4E70AA82.5050409@redhat.com>
Date:	Wed, 14 Sep 2011 16:22:10 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
CC:	x86@...nel.org, Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>,
	Peter Zijlstra <peterz@...radead.org>, ying.huang@...el.com,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com,
	jeremy@...p.org
Subject: Re: [V4][PATCH 4/6] x86, nmi:  add in logic to handle multiple events
 and unknown NMIs

On 09/14/2011 04:00 PM, Don Zickus wrote:
> On Wed, Sep 14, 2011 at 10:08:13AM +0300, Avi Kivity wrote:
> >  On 09/13/2011 11:58 PM, Don Zickus wrote:
> >  >Previous patches allow the NMI subsystem to process multipe NMI events
> >  >in one NMI.  As previously discussed this can cause issues when an event
> >  >triggered another NMI but is processed in the current NMI.  This causes the
> >  >next NMI to go unprocessed and become an 'unknown' NMI.
> >  >
> >  >To handle this, we first have to flag whether or not the NMI handler handled
> >  >more than one event or not.  If it did, then there exists a chance that
> >  >the next NMI might be already processed.  Once the NMI is flagged as a
> >  >candidate to be swallowed, we next look for a back-to-back NMI condition.
> >  >
> >  >This is determined by looking at the %rip from pt_regs.  If it is the same
> >  >as the previous NMI, it is assumed the cpu did not have a chance to jump
> >  >back into a non-NMI context and execute code and instead handled another NMI.
> >  >
> >  >If both of those conditions are true then we will swallow any unknown NMI.
> >  >
> >  >There still exists a chance that we accidentally swallow a real unknown NMI,
> >  >but for now things seem better.
> >
> >  Patch looks good, but the changelog is outdated.
>
> Perhaps, but I tried rewriting most of it to reflect the current changes.
> Was there something obvious in there that I missed?  I re-read it a few
> times and can't figure out what part might be outdated (not that I
> disagree with you, I just want to update it).
>

It's not really outdated (I guess I misread it).  However it emphasises 
the nmi swallowing part (which I guess was the focus of the first 
version) and doesn't really talk about doing just one source in ordinary 
NMIs and processing all sources in second (and third...) back-to-back 
NMIs.  I'd add something about that.

-- 
error compiling committee.c: too many arguments to function

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