This is fixed in the latest unstable tree.
Best,
Ian
> I was looking at the interrupt entry code in Xen, and noticed
> that segment
> registers get saved depending on the CPU level which was interrupted.
> Specifically, the ds, es, fs and gs registers are saved only
> if ring 1, 2 or 3
> was interrupted, and not if ring 0 was interrupted.
>
> What is the motivation for this?
>
> It appears to me that this is responsible for sometimes
> causing "lost" NMI
> interrupts. Basically, if an NMI occurs when a Xen activation
> was saving or
> restoring these registers, the handler just returns without
> calling the NMI
> watchdog. Is this because it may not be possible to restore
> the segments
> otherwise? Can this be fixed by making the NMI handler always
> save all segment
> registers?
>
> "Losing" an NMI is problematic in the following scenario
> which I am considering:
> I want to use the NMI interrupt in conjunction with the
> hardware performance
> counters for statistical profiling. The hardware counters are
> programmed to
> generate an NMI at regular intervals, and the NMI handler
> collects PC samples
> for statistical profiling.
>
> Unfortunately, if the NMI is "lost", the profiling comes to a
> halt, because the
> hardware counters need to be restarted on each NMI. Thus, I
> need to make sure
> that no NMIs are lost.
>
> I would like to know if this problem can be solved by making
> sure that all
> interrupt handlers and the NMI handler save all segment
> registers on entry, and
> restore them on exit.
>
> Thanks.
>
> Aravind Menon
>
> Doctoral School
> EPFL, Switzerland
>
>
>
>
>
>
>
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