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RE: [Xen-users] vmware inside Xen

  • To: "Claus R. F. Overbeck" <xen@xxxxxxxxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "JHJE (Jan Holst Jensen)" <jhje@xxxxxxxxxxxxxxx>
  • Date: Mon, 30 May 2005 14:18:10 +0200
  • Delivery-date: Mon, 30 May 2005 12:17:41 +0000
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: AcVlDa3MhPqGlE3fT4WXlkAk3ynk5AAAy3iA
  • Thread-topic: [Xen-users] vmware inside Xen

> I am not an expert on this but I think the reason is that 
> most of the machine 
> code that runs inside the vmware ist passed straight to the 
> cpu instead of 
> simulating a x86 cpu (this is good for speed). Therefore 
> vmware expects to 
> run on a x86 cpu which Xen does not provide.

Hi Claus.

Xen _does_ provide an x86 CPU, but direct access to the hardware and
memory management is not allowed - it must go through the Xen
hypervisor. When running machine code in user space you are running
directly on the CPU just as if you were running VMware. Kernel code runs
more efficiently on Xen since the kernel knows that it is virtualized
and the processor thus does not have to trap hardware access as when
running VMware.

> This brings me to the (probably stupid) question: Do I need 
> to recompile every 
> package that I want to run inside Xen because the 
> architecture is different?
> (I think the answer is "no" but why?)

No - user space applications won't (or at least shouldn't) know the
difference. As long as you are in user space you see a normal CPU on a
seemingly normal OS kernel.

-- Jan Holst Jensen, Novo Nordisk A/S, Denmark

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