Re: [V4][PATCH 4/6] x86, nmi: add in logic to handle multipleevents and unknown NMIs

[Don Zickus]

On Wed, Sep 14, 2011 at 04:22:10PM +0300, Avi Kivity wrote:
> 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  Patch looks good, but the changelog is outdated.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times and can't figure out what part might be outdated (not that I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 It's not really outdated (I guess I misread it).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.

Ah, yes.  I can add that.

Thanks,
Don
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