[Fedora-xen] Questions about virtualization and Xen

[Rik van Riel]

On Sun, 28 May 2006, Filipe Miranda wrote:

> I would like to clear a few questions that I have about virtualization, 
> please correct me if I'm wrong...

Sorry dude, but you seem to have some things mixed up ;)

> 1) Xen is a virtual machine monitor that uses the hardware virtualization
> approach knows as para-virtualization.

Xen is a virtual machine monitor.

However, hardware virtualization is very much distinct from
para-virtualization.

Para-virtualization is the act of partially virtualizing a
computer, and not providing full virtualization.  This means
that when a virtual machine runs in paravirtualized mode,
you can NOT run a normal operating system.  Instead, you have
to use a specially modified operating system.  Paravirtualization
does not need any special hardware support.

Hardware virtualization, on the other hand, is based around
special hardware making full virtualization easier.  This way
you can run a normal unmodified operating system inside your
virtual machine.

> 2) Para-virtualization is a technology that provides the virtual machine 
> monitor access directly to the machine's hardware without having an 
> underlying operation system to manage that, so less layer of abstraction 
> are between the virtual machines OS guest and the true hardware.

No.  Virtualized hardware would be useful for both full
virtualization and paravirtualization, and is a related
technology.  It is not part of paravirtualization though.

> 3) Xen 3.0 makes possible to guests virtual machines to access the machine's
> hardware either through Xens APIs or through hardware enabled virtualization
> like Intel VT-x or AMD Pacifica technologies, so you can have either a
> modified guest  OS like Linux or  an unmodified OS guest like Windows2003
> running on top of Xen 3.0.

Yes.

On "normal" hardware you can only run paravirtualized (modified)
guests.

On VT-x or SVM hardware, you can run unmodified guest OSes too.

-- 
All Rights Reversed