RE: [Xen-devel] Saving segment registers on interrupt / lost NMI

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

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
> 
> 
> 
> 
> 
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by: IntelliVIEW -- Interactive 
> Reporting
> Tool for open source databases. Create drag-&-drop reports. Save time
> by over 75%! Publish reports on the web. Export to DOC, XLS, RTF, etc.
> Download a FREE copy at http://www.intelliview.com/go/osdn_nl
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/xen-devel
> 


-------------------------------------------------------
This SF.Net email is sponsored by: IntelliVIEW -- Interactive Reporting
Tool for open source databases. Create drag-&-drop reports. Save time
by over 75%! Publish reports on the web. Export to DOC, XLS, RTF, etc.
Download a FREE copy at http://www.intelliview.com/go/osdn_nl
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel