1.\" Copyright (c) 2010 Robert N. M. Watson 2.\" All rights reserved. 3.\" 4.\" This software was developed by SRI International and the University of 5.\" Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237 6.\" ("CTSRD"), as part of the DARPA CRASH research program. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 18.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 21.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.Dd January 8, 2024 30.Dt XEN 4 31.Os 32.Sh NAME 33.Nm xen 34.Nd Xen Hypervisor Support 35.Sh SYNOPSIS 36FreeBSD supports running both as a Xen guest and host on amd64 hardware. 37Guest support is limited to HVM and PVH modes, while host support is limited to 38PVH mode only. 39.Pp 40Xen support is built by default in the i386 and amd64 GENERIC kernels; note 41however that host mode is only available on amd64. 42.Ed 43.Sh DESCRIPTION 44The Xen Hypervisor allows multiple virtual machines to be run on a single 45computer system. 46When first released, Xen required that i386 kernels be compiled 47"para-virtualized" as the x86 instruction set was not fully virtualizable. 48Primarily, para-virtualization modifies the virtual memory system to use 49hypervisor calls (hypercalls) rather than direct hardware instructions to 50modify the TLB, although para-virtualized device drivers were also required 51to access resources such as virtual network interfaces and disk devices. 52.Pp 53With later instruction set extensions from AMD and Intel to support fully 54virtualizable instructions, unmodified virtual memory systems can also be 55supported; this is referred to as hardware-assisted virtualization (HVM and PVH). 56HVM configurations may either rely on transparently emulated hardware 57peripherals, or para-virtualized drivers, which are aware of virtualization, 58and hence able to optimize certain behaviors to improve performance or 59semantics. 60PVH configurations rely on para-virtualized drivers exclusively for IO. 61.Pp 62.Fx 63Para-virtualized device drivers are required in order to support certain 64functionality, such as processing management requests, returning idle 65physical memory pages to the hypervisor, etc. 66.Ss Xen device drivers 67These para-virtualized drivers are supported: 68.Bl -hang -offset indent -width blkfront 69.It Nm balloon 70Allow physical memory pages to be returned to the hypervisor as a result of 71manual tuning or automatic policy. 72.It Nm blkback 73Exports local block devices or files to other Xen domains where they can 74then be imported via 75.Nm blkfront . 76.It Nm blkfront 77Import block devices from other Xen domains as local block devices, to be 78used for file systems, swap, etc. 79.It Nm console 80Export the low-level system console via the Xen console service. 81.It Nm control 82Process management operations from Domain 0, including power off, reboot, 83suspend, crash, and halt requests. 84.It Nm evtchn 85Expose Xen events via the 86.Pa /dev/xen/evtchn 87special device. 88.It Nm gntdev 89Allow access to the grant table interface via the 90.Pa /dev/xen/gntdev 91special device. 92.It Nm netback 93Export local network interfaces to other Xen domains where they can be 94imported via 95.Nm netfront . 96.It Nm netfront 97Import network interfaces from other Xen domains as local network interfaces, 98which may be used for IPv4, IPv6, etc. 99.It Nm privcmd 100Allow issuing hypercalls via the 101.Pa /dev/xen/privcmd 102special device. 103.It Nm timer 104Implementation of a one-shot high resolution per-CPU timer using the hypercall 105interface. 106.It Nm acpi cpu 107When running as a host forwards power management related information from ACPI 108to the hypervisor for better performance management. 109.It Nm xenpci 110Represents the Xen PCI device, an emulated PCI device that is exposed to 111HVM domains. 112This device allows detection of the Xen hypervisor, and provides interrupt 113and shared memory services required to interact with the hypervisor. 114.It Nm xenstore 115Information storage space shared between domains. 116.El 117.Sh HISTORY 118Support for 119.Nm 120first appeared in 121.Fx 8.1 . 122Support for host mode was added in 11.0 . 123.Sh AUTHORS 124.An -nosplit 125.Fx 126support for Xen was first added by 127.An Kip Macy Aq Mt kmacy@FreeBSD.org 128and 129.An Doug Rabson Aq Mt dfr@FreeBSD.org . 130Further refinements were made by 131.An Justin Gibbs Aq Mt gibbs@FreeBSD.org , 132.An Adrian Chadd Aq Mt adrian@FreeBSD.org , 133.An Colin Percival Aq Mt cperciva@FreeBSD.org , 134and 135.An Roger Pau Monné Aq Mt royger@FreeBSD.org . 136This manual page was written by 137.An Robert Watson Aq Mt rwatson@FreeBSD.org , 138and 139.An Roger Pau Monné Aq Mt royger@FreeBSD.org . 140