RE: [Xen-devel] Task Switching and Xen-SVM

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: Ian Pratt [mailto:m+Ian.Pratt@xxxxxxxxxxxx] 
> Sent: 27 October 2006 10:07
> To: Petersson, Mats; Vivek Mohan; xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: ian.pratt@xxxxxxxxxxxx
> Subject: RE: [Xen-devel] Task Switching and Xen-SVM
> 
> > Do you actually know of any (32-bit) OS that uses task switching? 
> 
> It's often used in double fault, NMI and MCA handlers, all of 
> which are
> typically fatal.
> 
> It would still be good to have them implemented to get a decent oops
> message out though.

Good point. On the other hand, double-fault is caught by SVM (vmx.c
doesn't seem to do the same here) and debug info printed to the console
before we ship the DF back into the guest, so it should be detectable
what went wrong there. 

NMI and MCA shouldn't happen in the guest - at least not in the current
architecture where NMI and MCA are all handled in Xen. Is there a
reasonable cause for this to change anytime soon? [How do we know what
guest cause MCE - as memory related MCE's happen on the processor owning
the memory, and may also be caused by the "memory scrubber". And it
doesn't really make much sense to give MCE's to the guest, as it's
generally a hardware related problem.]

NMI's to guest may make more sense if we take for example performance
counters... Not sure if this is important or not... Performance counting
in the guest is another "interesting" topic where it's hard for the
guest to make sense of the numbers without knowing about the hypervisor,
I think... 

--
Mats
> 
> Ian 
> 
> > In my
> > experience, it's horribly slow (because it generally saves/restores
> more
> > of the context than is necessary). Of course, in 64-bit 
> mode it's not
> > even allowed, all task-management features have been removed... I'm
> > saying 32-bit OS, since there's probably some 16-bit OS's out there
> that
> > do use task-switching, but those OS's are not able to run on current
> Xen
> > anyways, since Xen in it's current form is very poor at supporting
> > segments with base != 0 in protected mode. So far I've only 
> seen a few
> > rare reports of anyone actually wishing to run a 16-bit OS...
> > 
> > --
> > Mats
> > >
> > > Thanks,
> > > Vivek
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> > >
> > >
> > >
> > 
> > 
> > 
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> > http://lists.xensource.com/xen-devel
> 
> 
> 



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