Re: Xen Internals(Trap handler)

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, Mar 25, 2007 at 10:36:02PM -0700, Vibhooti Verma wrote:
> 
> How does trap handler know about origin of trap?
> Whether it is generated from guest os's user process or guest os
> kernel?since it has to execute privileged instruction only when it is coming
> from guest OS., kernel.

On i386, the kernel and userland runs in different ring levels (userland
is still at level 3, the kernel is at level 1 - level 0 is reserved for the
hypervisor of course).
So the hypervisor just needs to check the ring level of the trapping
instruction in %cs

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--