Re: Xen Internals(Trap handler)

[Vibhooti Verma <vibhooti_verma%yahoo.com@localhost>]

Manuel Bouyer wrote:
> 
> 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
> --
> 
> 

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