xref: /freebsd/share/man/man4/xen.4 (revision 7c472105ac5a36549a5445b0b2c7d34e9621a769)

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.Dd December 13, 2010
.Dt XEN 4
.Os
.Sh NAME
.Nm xen
.Nd Xen Hypervisor Guest (DomU) Support
.Sh SYNOPSIS
To compile para-virtualized (PV) Xen guest support into the i386 kernel, place
the following line in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options PAE"
.Cd "options XEN"
.Ed
.Pp
To compile hardware-assisted virtualization (HVM) Xen guest support into the
amd64 kernel, place the following line in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options XENHVM"
.Ed
.Pp
To compile the Xen PCI bus and para-virtualized (PV) drivers into an amd64
or i386 kernel, place the following line in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device xenpci"
.Ed
.Sh DESCRIPTION
The Xen Hypervisor allows multiple virtual machines to be run on a single
computer system.
When first released, Xen required that i386 kernels be compiled
"para-virtualized" as the x86 instruction set was not fully virtualizable.
With later instruction set extensions from AMD and Intel to support fully
virtualizable instructions, unmodified kernels could also be supported,
referred to as hardware-assisted virtualization (HVM).
HVM systems may still use para-virtualized drivers, which are aware of
virtualization and able to optimize certain behaviours to improve
performance or semantics.
.Pp
.Fx
supports a fully para-virtualized (PV) kernel on the i386 architecture using
.Cd "options XEN" ;
currently, this requires use of a PAE kernel, enabled via
.Cd "options PAE" .
.Fx
supports hardware-assited virtualization (HVM) on both the i386 and amd64
kernels; however, PV device drivers with an HVM kernel are only supported on
the amd64 architecture.
.Pp
Para-virtualized device drivers are required in order to support certain
functionality, such as the dynamic addition of new virtual devices, and the
"balloon driver" (returning physical memory to the Hypervisor on demand),
and VM suspend/resume.
.Sh SEE ALSO
.Xr pae 4
.Sh HISTORY
Support for
.Nm
first appeared in
.Fx 8.1 .
.Sh AUTHORS
.An -nosplit
.Fx
support for Xen was first added by
.An Kip Mac Aq kmacy@FreeBSD.org
and
.An Doug Rabson Aq dfr@FreeBSD.org .
Further refinements were made by
.An Justin Gibbs Aq gibbs@FreeBSD.org ,
.An Adrian Chadd Aq adrian@FreeBSD.org ,
and
.An Colin Percival Aq cperciva@FreeBSD.org .
This manual page was written by
.An Robert Watson Aq rwatson@FreeBSD.org .
.Sh BUGS
.Fx
is only able to run as a Xen guest (DomU) and not as a Xen host (Dom0).
.Pp
A fully para-virtualized (PV) kernel is only supported on i386, and not
amd64.
.Pp
Para-virtualized drivers under hardware-assisted virtualization (HVM) kernel
are only supported on amd64, not i386.
.P
As of this release, Xen DomU support is not heavily tested; instability has
been reported during VM migration of PV kernels, and certain PV driver
features, such as the balloon driver, are under-exercised.