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    SubjectRe: [V4][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs
    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 Patch looks good, but the changelog is outdated.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times and can't figure out what part might be outdated (not that I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 It's not really outdated (I guess I misread it).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.


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