Add a rudimentary Xen man page summarising the state of Xen on amd64 and
i386, how to configure the kernel, and some known issues. Further refinement almost certainly required. This is not a Xen installation manual. MFC after: 3 days Sponsored by: DARPA, AFRL
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share/man/man4/xen.4
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share/man/man4/xen.4
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.\" Copyright (c) 2010 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" This software was developed by SRI International and the University of
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.\" Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237
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.\" ("CTSRD"), as part of the DARPA CRASH research program.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd December 13, 2010
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.Dt XEN 4
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.Os
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.Sh NAME
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.Nm xen
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.Nd Xen Hypervisor Guest (DomU) Support
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.Sh SYNOPSIS
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To compile para-virtualized (PV) Xen guest support into the i386 kernel, place
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the following line in your kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options PAE"
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.Cd "options XEN"
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.Ed
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.Pp
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To compile hardware-assisted virtualization (HVM) Xen guest support into the
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amd64 kernel, place the following line in your kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options XENHVM"
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.Ed
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.Pp
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To compile the Xen PCI bus and para-virtualized (PV) drivers into an amd64
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or i386 kernel, place the following line in your kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device xenpci"
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.Ed
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.Sh DESCRIPTION
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The Xen Hypervisor allows multiple virtual machines to be run on a single
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computer system.
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When first released, Xen required that i386 kernels be compiled
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"para-virtualized" as the x86 instruction set was not fully virtualizable.
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With later instruction set extensions from AMD and Intel to support fully
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virtualizable instructions, unmodified kernels could also be supported,
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referred to as hardware-assisted virtualization (HVM).
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HVM systems may still use para-virtualized drivers, which are aware of
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virtualization and able to optimize certain behaviours to improve
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performance or semantics.
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.Pp
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.Fx
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supports a fully para-virtualized (PV) kernel on the i386 architecture using
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.Cd "options XEN" ;
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currently, this requires use of a PAE kernel, enabled via
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.Cd "options PAE" .
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.Fx
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supports hardware-assited virtualization (HVM) on both the i386 and amd64
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kernels; however, PV device drivers with an HVM kernel are only supported on
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the amd64 architecture.
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.Pp
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Para-virtualized device drivers are required in order to support certain
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functionality, such as the dynamic addition of new virtual devices, and the
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"balloon driver" (returning physical memory to the Hypervisor on demand),
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and VM suspend/resume.
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.Sh SEE ALSO
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.Xr pae 4
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.Sh HISTORY
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Support for
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.Nm
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first appeared in
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.Fx 8.1 .
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.Sh AUTHORS
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.An -nosplit
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.Fx
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support for Xen was first added by
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.An Kip Mac Aq kmacy@FreeBSD.org
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and
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.An Doug Rabson Aq dfr@FreeBSD.org .
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Further refinements were made by
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.An Justin Gibbs Aq gibbs@FreeBSD.org ,
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.An Adrian Chadd Aq adrian@FreeBSD.org ,
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and
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.An Colin Percival Aq cperciva@FreeBSD.org .
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This manual page was written by
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.An Robert Watson Aq rwatson@FreeBSD.org .
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.Sh BUGS
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.Fx
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is only able to run as a Xen guest (DomU) and not as a Xen host (Dom0).
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.Pp
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A fully para-virtualized (PV) kernel is only supported on i386, and not
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amd64.
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.Pp
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Para-virtualized drivers under hardware-assisted virtualization (HVM) kernel
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are only supported on amd64, not i386.
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.P
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As of this release, Xen DomU support is not heavily tested; instability has
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been reported during VM migration of PV kernels, and certain PV driver
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features, such as the balloon driver, are under-exercised.
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