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Re: [Xen-users] how does hypervisor isolates DomU from Dom0

To: Nick Couchman <Nick.Couchman@xxxxxxxxx>
Subject: Re: [Xen-users] how does hypervisor isolates DomU from Dom0
From: Tapas Mishra <mightydreams@xxxxxxxxx>
Date: Tue, 17 Aug 2010 08:09:56 +0530
Cc: Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
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On Mon, Aug 16, 2010 at 10:21 PM, Nick Couchman <Nick.Couchman@xxxxxxxxx> wrote:
>>>> On 2010/08/15 at 14:19, Tapas Mishra <mightydreams@xxxxxxxxx> wrote:
>> I am not clear with the working of hypervisor xen.
>> How does an instruction executed by kernel in Ring0 of DomU gets
>> mapped or executed by hypervisor and then is excuted in Dom0.
>> Is this thing some where on the wiki page?
> I'm not all that familiar with the internals of Xen, but I think the 
> high-level answer to your question is, it depends.  It depends on what type 
> of domU you're running.  Paravirtualized domUs are aware that they are 
> virtualized and that they do not have ring 0 access, so I'm guessing they do 
> not attempt to execute instructions in ring 0 without passing it through to 
> the hypervisor, which brokers those requests.  HVM domUs, on the other hand, 
> are full machines (more along the lines of how VMware does virtualization) 
> that can run an unmodified kernel.  So, kernels in HVM domUs attempt to 
> access ring 0 resources, which must then be translated by the HVM and passed 
> on to the hypervisor.
> That's my understanding of how it works...
> -Nick
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