Xen has support for two different kinds of guests. Paravirtualized guests
are aware that they are running inside a virtual environment, and have been
modified to operate well in this environment. All linux kernels above 2.6.27
(I think) with the pv_ops extensions compiled in can run as a Xen VM in this
mode. This mode also does not require any particular CPU support.

With proper CPU support Xen can also be a hypervisor style environment, in
which case the guest is not aware that it is running inside a virtual
environment. FreeBSD of any vintage can run successfully in this mode.
Unfortunately, there are greater performance penalties to running a guest in
HVM mode as opposed to PVM mode.


On Thu, Mar 18, 2010 at 4:47 PM, Martin Cracauer <> wrote:

> I never got this so I rather ask:
> Xen should run OS kernels unmodified (compared to their native
> hardware versions) if you have hardware virtualization support in the
> CPU.
> Why doesn't this cover FreeBSD?
> I am missing something here.
> Martin
> --
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> Martin Cracauer <>
> FreeBSD - where you want to go, today.
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