Thanks Manuel
Normally Only two rings( 0 --for kernel and 3--for user) are used. So how
exactly we make use of 3 rings?
How do we force the guest kernels to run in ring-1 and hypervisor is ring-0.
How does xen implemt it?


Vibhooti Verma wrote:
> 
> 
> 
> 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>
>>      NetBSD: 26 ans d'experience feront toujours la difference
>> --
>> 
>> 
> 
> 

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