Re: xen & FPU

["Christian Limpach" <Christian.Limpach%cl.cam.ac.uk@localhost>]

From: "Matthias Scheler" <tron%zhadum.de@localhost>
> On Sat, Mar 19, 2005 at 10:17:53AM -0000, Christian Limpach wrote:
> > It handles FPU errors, the context switching part of FPU exception 
> > handling
> > is in npxdna_*.  Both types of exceptions get always passed up to the
> > domain causing the exception.  I would try removing the panic and also
> > commenting out the bus_space_write which is just following it.  The rest 
> > of
> > the code looks like it could just work...
>
> Who will clear the interrupt latch? The Hypervisor?

Clearing the interrupt latch is only necessary when you're running on a 386 
or older where you (choose to) get FPU errors on interrupt 13.  On newer 
chips, you (choose to) get FPU errors on trap #16 and there's no interrupt 
latch to clear.  I wonder what the bus_space_write actually writes to on 
NetBSD/i386...

Xen always acknowledges hardware interrupts, the guest only needs to 
acknoweledge the virtual interrupt it gets on the event channel which is 
used to propagate the hardware interrupt to the guest (or guests in case of 
interrupt line sharing with drivers in different domains -- really not a 
sane setup though...).

   christian