Xen [FreeBSD WIKI]

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====== Xen Hypervisor Dom0 and DomU Support ======

Xen is a GPLv2-license hypervisor for the Intel architecture

%%FreeBSD%% 8.0 onward includes i386 and amd64 %%DomU%% and Amazon EC2 unprivileged domain (virtual machine) support.

%%FreeBSD%% 11.0 onward includes Xen Dom0 privileged domain (host) support.

===== FreeBSD Dom0 Control Domain Support =====

==== Hardware Requirements ====

Hardware virtualized domains require Extended Page Table ([[http://en.wikipedia.org/wiki/Extended_Page_Table|EPT]]) and Input/Output Memory Management Unit ([[http://en.wikipedia.org/wiki/List_of_IOMMU-supporting_hardware|IOMMU]]) processor features to operate.

NB! %%FreeBSD%% Xen cannot be loaded with UEFI at this time

==== Dom0 Control Domain Installation ====

The 'xen-kernel' and 'xen-tools' packages provide the Xen Dom0 kernel and support utilities. The following example will assume VNC output for unprivileged domains which will be accessed from a another system using a tool such as ''%%net/tightvnc%%''.

=== Xen Dom0 Package Installation ===

<code>
pkg install -y xen-kernel xen-tools
</code>

Follow the instructions provided at the end of the package which modifies:

<code>
/etc/sysctl.conf
/etc/ttys
/boot/loader.conf
</code>

In addition to these instructions, Xen also requires:

<code>
/etc/rc.conf

cloned_interfaces="bridge0"
ifconfig_bridge0="addm <primary network interface i.e. igb0> up"
</code>

Reboot the host to boot to the Xen kernel.

You should see the Xen kernel output followed the %%FreeBSD%% kernel output. The %%FreeBSD%% control domain system will behave in the established manner and note the ''%%dom0_mem%%'' and ''%%dom0_max_vcpus%%'' options in ''%%/boot/loader.conf%%'', particularly on root-on-ZFS systems with ZFS ARC read caching.

=== Unprivileged Domain Configuration ===

Unprivileged Domains consist of a configuration file and logical or physical optical and hard disks. For this example we will assume a ISO optical disk file ''%%freebsd.iso%%'' and a hard disk file created with ''%%truncate -s 20G freebsd.img%%''.

An example %%FreeBSD%% %%DomU%% configuration file ''%%freebsd.cfg%%'' with 2048M RAM and two virtual CPUs without networking:

<code>
type = "hvm"
memory = 2048
vcpus = 2
vif = [ 'bridge=bridge0' ]
name = "FreeBSD"
disk = [ '/root/freebsd.img,raw,hda,w',
         '/root/freebsd.iso,raw,hdc:cdrom,r' ]
# boot = "c" # Boot to hard disk image
boot = "d" # Boot to ISO image
vnc = 1
vnclisten = 0.0.0.0
vncdisplay=1 # VNC Port 5900
on_poweroff = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'
</code>

To boot this %%DomU%% with ''%%-vvvv%%'' level of verbose logging:

<code>
# xl -vvvv create freebsd.cfg

# xl list
Name                        ID   Mem VCPUs      State   Time(s)
Domain-0                     0  2047     4     r-----     660.6
FreeBSD                      1  2048     2     r-----       3.5
</code>

To connect to this %%DomU%% using ''%%net/tightvnc%%'' on the host:

<code>
# vncviewer 0.0.0.0
</code>

The %%DomU%% should reboot and shutdown properly but to manually destroy it:

<code>
# xl destroy FreeBSD
</code>

An example Windows %%DomU%% configuration file ''%%windows.cfg%%'' with 4096M RAM and a two virtual CPUs without networking:

<code>
type = "hvm"
memory = 4096
vcpus = 2
name = "Windows"
disk = [ '/root/windows.img,raw,hda,w',
         '/root/windows.iso,raw,hdc:cdrom,r' ]
# boot = "c" # Boot to hard disk image
boot = "d" # Boot to ISO image
vnc = 1
vnclisten = 0.0.0.0
vncdisplay=1 # VNC Port 5901
on_poweroff = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'
acpi = 1
</code>

The network interface will appear as ''%%xn0%%'' and note that the ''%%tap%%'' and ''%%bridge%%'' devices must be present or the %%DomU%% will not boot.

=== Serial Configuration ===

The additional configuration option ''%%serial='pty'%%'' should allow for attachment to the %%DomU%% serial console with ''%%xl create -c <DomU>.cfg%%''. Be sure that your %%DomU%% is configured for serial console output. For a %%FreeBSD%% %%DomU%% add the following to ''%%/boot/loader.conf%%'':

<code>
boot_serial="YES"
comconsole_speed="115200"
console="comconsole"
</code>

Also run:

''%%printf "%s" "-h -S115200" /boot.config%%''

Once connected, ''%%CTRL-]%%'' will disconnect from the %%DomU%% console.

=== Live migration, save and restore ===

The version of Xen available in the ports tree supports live migration, save and restore of live guests. Keep in mind that in order to use live migration your virtual disk must be shared between the different Xen Dom0s (NFS, iSCSI...), and it must reside in the same path on the Dom0 filesystem. The usage is the following:

<code>
# xl migrate <vm name> <destination host>
</code>

The default transport used by xl is ssh, check the man page (xl(1%%))%% for other options.

With save and restore you can take a snapshot of the current guest state and save it to disk as a regular file, including memory and device state. This allows you to restore a guest to a specific state without having to boot it again:

<code>
# xl save <vm name> <file>
</code>

Then in order to restore the guest:

<code>
# xl restore <file>
</code>

You can also take a snapshot of the disk in order to be able to do a complete checkpoint of a guest state.

==== Known Limitations ====

  * Suspend and Resume may not work
  * The console mouse may not work on the host
  * The %%FreeBSD%% kernel debugger may not work
  * MSI-X PV interrupts are not supported (%%FreeBSD%%)
  * PCI devices with virtual functions work inconsistently (%%FreeBSD%%)
  * PCI Passthrough is not supported (Xen/%%FreeBSD%%)
  * ARM64 is not supported
  * Loading vmm.ko will panic the Dom0, as may VirtualBox

==== Miscellaneous ====

''%%Error creating domain 0%%'' on boot indicates that VT-x extensions are unavailable or disabled in BIOS.

If your %%DomU%% "%%FreeBSD%%" does not boot, check the log in ''%%/var/log/xen/qemu-dm-FreeBSD.log%%''

ZFS zvol-backed %%DomU%% virtual machines are supported with:

<code>
disk = ['/dev/zvol/zroot/freebsd,raw,hda,rw']
disk = ['phy:/dev/zvol/zroot/linux,xvda,w']
</code>

Some %%DomU%% virtual machines such as %%OpenBSD%% may support only one virtual CPU.

If your VNC display freezes or does not scale during the various %%DomU%% boot stages, try reconnecting.

%%DomU%% configuration files are not re-read on reboot.

The ''%%freebsd-virtualization%%'' mailing list and official Xen project resources may be helpful but at this stage you may be the first person to try your given configuration.

The established Xen documentation is generally applicable to %%FreeBSD%%.

More Dom0 development information can be found at: [[https://wiki.xen.org/wiki/FreeBSD_Dom0]]

More Amazon EC2 unprivileged domain information can be found at: [[http://www.daemonology.net/freebsd-on-ec2/]]

==== Tested DomU Operating Systems ====

  * %%FreeBSD%% 11
  * %%OpenBSD%% 5.6
  * %%NetBSD%% 6.1.5
  * Windows XP
  * Windows 8.1 Pro
  * Windows 10 Beta
  * Windows Server 2008R2
  * GNU/Linux (Ubuntu/Debian/Fedora...)

Any guest operating system supported by Xen on other platforms should be supported on %%FreeBSD%%.

:!: This page replaces some, if not all of the other Xen pages on this wiki

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{{tag>Virtualization Stale}}