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version 1.170, 2020/10/31 15:29:23	version 1.189, 2020/11/19 13:55:58
Line 8 systems which operate in an unprivileged	Line 8 systems which operate in an unprivileged
from the domU systems are forwarded by the Xen hypervisor to the dom0 to be	from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
fulfilled.	fulfilled.

Xen supports different styles of guest:	This HOWTO presumes a basic familiarity with the Xen system
	architecture, with installing NetBSD on amd64 hardware, and with
	installing software from pkgsrc. See also the [Xen
	website](http://www.xenproject.org/).

	[[!toc]]

	# Overview

	The basic concept of Xen is that the hypervisor (xenkernel) runs on
	the hardware, and runs a privileged domain ("dom0") that can access
	disks/networking/etc. One then runs additonal unprivileged domains
	(each a "domU"), presumably to do something useful.

	This HOWTO addresses how to run a NetBSD dom0 (and hence also build
	xen itself). It also addresses how to run domUs in that environment,
	and how to deal with having a domU in a Xen environment run by someone
	else and/or not running NetBSD.

	There are many choices one can make; the HOWTO recommends the standard
	approach and limits discussion of alternatives in many cases.

	## Guest Styles

	Xen supports different styles of guests.

[[!table data="""	[[!table data="""
Style of guest \|Supported by NetBSD	Style of guest \|Supported by NetBSD
PV \|Yes (dom0, domU)	PV \|Yes (dom0, domU)
HVM \|Yes (domU)	HVM \|Yes (domU)
PVHVM \|current-only (dom0, domU)	PVHVM \|current-only (domU)
PVH \|current-only (dom0, domU)	PVH \|current-only (domU, dom0 not yet)
"""]]	"""]]

In Para-Virtualized (PV) mode, the guest OS does not attempt to access	In Para-Virtualized (PV) mode, the guest OS does not attempt to access
hardware directly, but instead makes hypercalls to the hypervisor; PV	hardware directly, but instead makes hypercalls to the hypervisor; PV
guests must be specifically coded for Xen.	guests must be specifically coded for Xen.
	See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).

In HVM mode, no guest modification is required; however, hardware	In HVM mode, no guest modification is required; however, hardware
support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.	support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
	The dom0 runs qemu to emulate hardware.

In PVHVM mode, the guest mostly runs as HVM, but can use PV drivers for efficiency. See https://wiki.xen.org/wiki/PV_on_HVM	In PVHVM mode, the guest runs as HVM, but additionally can use PV
	drivers for efficiency.
In PVH mode, the guest uses PV interfaces for IO and native interfaces for everything else. This is also called PVHv2; see https://wiki.xenproject.org/wiki/PVH_(v2)_Domu	See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).

	There have been two PVH modes: original PVH and PVHv2. Original PVH
	was based on PV mode and is no longer relevant at all. PVHv2 is
	basically lightweight HVM with PV drivers. A critical feature of it
	is that qemu is not needed; the hypervisor can do the emulation that
	is required. Thus, a dom0 can be PVHv2.
	The source code uses PVH and config files use pvh; this refers to PVHv2.
	See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).

At boot, the dom0 kernel is loaded as a module with Xen as the kernel.	At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
The dom0 can start one or more domUs. (Booting is explained in detail	The dom0 can start one or more domUs. (Booting is explained in detail
in the dom0 section.)	in the dom0 section.)

This HOWTO presumes a basic familiarity with the Xen system	## CPU Architecture
architecture, with installing NetBSD on i386/amd64 hardware, and with
installing software from pkgsrc. See also the [Xen
website](http://www.xenproject.org/).

[[!toc]]	Xen runs on x86_64 hardware (the NetBSD amd64 port).

	There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.

	The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)

#Versions and Support	The domU can be i386PAE or amd64.
	i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.

	## Xen Versions

In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages	In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
xenkernel and xentools. We will refer only to the kernel versions,	xenkernel and xentools. We will refer only to the kernel versions,
Line 50 matching versions.	Line 88 matching versions.
Versions available in pkgsrc:	Versions available in pkgsrc:

[[!table data="""	[[!table data="""
Xen Version \|Package Name \|Xen CPU Support \|xm? \|EOL'ed By Upstream	Xen Version \|Package Name \|Xen CPU Support \|EOL'ed By Upstream
4.2 \|xenkernel42 \|i386 x86_64 \|yes \|Yes	4.11 \|xenkernel411 \|x86_64 \|No
4.5 \|xenkernel45 \|x86_64 \| \|Yes	4.13 \|xenkernel413 \|x86_64 \|No
4.6 \|xenkernel46 \|x86_64 \| \|Yes
4.8 \|xenkernel48 \|x86_64 \| \|Yes
4.11 \|xenkernel411 \|x86_64 \| \|No
"""]]	"""]]

See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).	See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).

Multiprocessor (SMP) support in NetBSD differs depending on the domain:

[[!table data="""
Domain \|Supports SMP
dom0 \|No
domU \|Yes
"""]]

Note: NetBSD support is called XEN3. However, it does support Xen 4,
because the hypercall interface has remained identical.

Older Xen had a python-based management tool called xm, now replaced	Older Xen had a python-based management tool called xm, now replaced
by xl. xm is obsolete, but 4.2 remains in pkgsrc because migrating	by xl.
from xm to xl is not always trivial, and because 4.2 is the last
version to run on an i386 dom0.

Architecture	## NetBSD versions
------------

Xen 4.5 and later runs on x86_64 hardware (the NetBSD amd64 port).	Xen has been supported in NetBSD for a long time, at least since 2005.
Xen 4.2 can in theory use i386 hardware, but we do not have	Initially Xen was PV only.
recent reports of success.

The dom0 system, plus each domU, can be either i386PAE or amd64.	NetBSD 8 and up support PV and HVM modes.
i386 without PAE is not supported.

The standard approach is to use NetBSD/amd64 for the dom0.	Support for PVHVM and PVH is available only in NetBSD-current.

To use an i386PAE dom0 (other than on 4.2), one must build or obtain a	NetBSD as a dom0 does not run SMP, because some drivers are not yet
64bit Xen kernel and install it on the system.	safe for this. \todo Link to more information about what needs work.

For domUs, i386PAE is considered as	NetBSD, when run as a domU, can and does typically run SMP.
[faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html)
than amd64.	Note: NetBSD support is called XEN3. However, it does support Xen 4,
	because the hypercall interface has remained identical.

# Creating a dom0	# Creating a NetBSD dom0

In order to install a NetBSD as a dom0, one must first install a normal	In order to install a NetBSD as a dom0, one must first install a normal
NetBSD system, and then pivot the install to a dom0 install by changing	NetBSD system, and then pivot the install to a dom0 install by changing
Line 105 In 2018-05, trouble booting a dom0 was r	Line 125 In 2018-05, trouble booting a dom0 was r
512M it worked reliably. This does not make sense, but if you see	512M it worked reliably. This does not make sense, but if you see
"not ELF" after Xen boots, try increasing dom0 RAM.	"not ELF" after Xen boots, try increasing dom0 RAM.

Installation of NetBSD	## Installation of NetBSD
----------------------

[Install NetBSD/amd64](/guide/inst/)	[Install NetBSD/amd64](/guide/inst/)
just as you would if you were not using Xen.	just as you would if you were not using Xen.
	Therefore, use the most recent release, or a build from the most recent stable branch.

Installation of Xen	## Installation of Xen
-------------------

We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as	Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.	Therefore, choose 4.13.
	In the dom0, install xenkernel413 and xentools413 from pkgsrc.

Once this is done, install the Xen kernel itself:	Once this is done, copy the Xen kernel from where pkgsrc puts it to
	where the boot process will be able to find it:

[[!template id=programlisting text="""	[[!template id=programlisting text="""
# cp /usr/pkg/xen48-kernel/xen.gz /	# cp -p /usr/pkg/xen413-kernel/xen.gz /
"""]]	"""]]

Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel	Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
Line 128 can either be compiled manually, or down	Line 149 can either be compiled manually, or down
example at:	example at:

[[!template id=programlisting text="""	[[!template id=programlisting text="""
ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz	ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
"""]]	"""]]

Add a line to /boot.cfg to boot Xen:	Add a line to /boot.cfg to boot Xen:
Line 138 menu=Xen:load /netbsd-XEN3_DOM0.gz conso	Line 159 menu=Xen:load /netbsd-XEN3_DOM0.gz conso
"""]]	"""]]

This specifies that the dom0 should have 512MB of ram, leaving the rest	This specifies that the dom0 should have 512MB of ram, leaving the rest
to be allocated for domUs. To use a serial console, use:	to be allocated for domUs.

	NB: This says add, not replace, so that you will be able to boot a
	NetBSD kernel without Xen. Once Xen boots ok, you may want to set it
	as default.

	To use a serial console, add settings as follows:

[[!template id=filecontent name="/boot.cfg" text="""	[[!template id=filecontent name="/boot.cfg" text="""
menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1	menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
Line 154 itself uses (in this case, the serial po	Line 181 itself uses (in this case, the serial po
In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,	In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
to force only one vcpu to be provided (since NetBSD dom0 can't use	to force only one vcpu to be provided (since NetBSD dom0 can't use
more) and to pin that vcpu to a physical CPU. Xen has	more) and to pin that vcpu to a physical CPU. Xen has
[many boot options](http://xenbits.xenproject.org/docs/4.8-testing/misc/xen-command-line.html),	[many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
and other than dom0 memory and max_vcpus, they are generally not	and other than dom0 memory and max_vcpus, they are generally not
necessary.	necessary.

Copy the boot scripts into `/etc/rc.d`:	Ensure that the boot scripts installed in
	`/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
[[!template id=programlisting text="""	have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
# cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/	but a normal part of pkgsrc usage.)
"""]]

Enable `xencommons`:	Set `xencommons=YES` in rc.conf:

[[!template id=filecontent name="/etc/rc.conf" text="""	[[!template id=filecontent name="/etc/rc.conf" text="""
xencommons=YES	xencommons=YES
"""]]	"""]]

	\todo Recommend for/against xen-watchdog.

Now, reboot so that you are running a DOM0 kernel under Xen, rather	Now, reboot so that you are running a DOM0 kernel under Xen, rather
than GENERIC without Xen.	than GENERIC without Xen.

TODO: Recommend for/against xen-watchdog.

Once the reboot is done, use `xl` to inspect Xen's boot messages,	Once the reboot is done, use `xl` to inspect Xen's boot messages,
available resources, and running domains. For example:	available resources, and running domains. For example:

Line 201 the state when the new xenstored starts.	Line 227 the state when the new xenstored starts.
make this work, one should not expect to be able to restart xenstored	make this work, one should not expect to be able to restart xenstored
(and thus xencommons). There is currently no reason to expect that	(and thus xencommons). There is currently no reason to expect that
this will get fixed any time soon.	this will get fixed any time soon.
	\todo Confirm if this is still true in 2020.

anita (for testing NetBSD)	## Xen-specific NetBSD issues
--------------------------

With the setup so far (assuming 4.8/xl), one should be able to run
anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
root, because anita must create a domU):

[[!template id=programlisting text="""
anita --vmm=xl test file:///usr/obj/i386/
"""]]

Xen-specific NetBSD issues
--------------------------

There are (at least) two additional things different about NetBSD as a	There are (at least) two additional things different about NetBSD as a
dom0 kernel compared to hardware.	dom0 kernel compared to hardware.
Line 228 options as GENERIC. While it is debatab	Line 243 options as GENERIC. While it is debatab
bug, users should be aware of this and can simply add missing config	bug, users should be aware of this and can simply add missing config
items if desired.	items if desired.

Updating NetBSD in a dom0	Finally, there have been occasional reports of trouble with X11
-------------------------	servers in NetBSD as a dom0.

	## Updating Xen in a dom0

	Basically, update the xenkernel and xentools packages and copy the new
	Xen kernel into place, and reboot. This procedure should be usable to
	update to a new Xen release, but the reader is reminded that having a
	non-Xen boot methods was recommended earlier.

	## Updating NetBSD in a dom0

This is just like updating NetBSD on bare hardware, assuming the new	This is just like updating NetBSD on bare hardware, assuming the new
version supports the version of Xen you are running. Generally, one	version supports the version of Xen you are running. Generally, one
Line 239 and adjusts `/etc`.	Line 263 and adjusts `/etc`.
Note that one must update both the non-Xen kernel typically used for	Note that one must update both the non-Xen kernel typically used for
rescue purposes and the DOM0 kernel used with Xen.	rescue purposes and the DOM0 kernel used with Xen.

Converting from grub to /boot	## anita (for testing NetBSD)
-----------------------------
	With a NetBSD dom0, even without any domUs, one should be able to run
	anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
	root, because anita must create a domU):

	[[!template id=programlisting text="""
	anita --vmm=xl test file:///usr/obj/i386/
	"""]]

	## Converting from grub to /boot (historical note)

	These instructions are provided only to help people using grub, which
	used to be the normal approach.

These instructions were used to convert a system from	These instructions were used to convert a system from
grub to /boot. The system was originally installed in February of	grub to /boot. The system was originally installed in February of
Line 270 default=1	Line 306 default=1
timeout=30	timeout=30
"""]]	"""]]

Upgrading Xen versions	# Unprivileged domains (domU)
---------------------

Minor version upgrades are trivial. Just rebuild/replace the
xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
references it), and reboot.

#Unprivileged domains (domU)

This section describes general concepts about domUs. It does not	This section describes general concepts about domUs. It does not
address specific domU operating systems or how to install them. The	address specific domU operating systems or how to install them. The
Line 292 mediated by Xen, and configured in the d	Line 321 mediated by Xen, and configured in the d
Entropy in domUs can be an issue; physical disks and network are on	Entropy in domUs can be an issue; physical disks and network are on
the dom0. NetBSD's /dev/random system works, but is often challenged.	the dom0. NetBSD's /dev/random system works, but is often challenged.

Config files	## Config files
------------

See /usr/pkg/share/examples/xen/xlexample*	See /usr/pkg/share/examples/xen/xlexample*
for a small number of well-commented examples, mostly for running	for a small number of well-commented examples, mostly for running
Line 320 are stored in files and Xen attaches the	Line 348 are stored in files and Xen attaches the
dom0 on domain creation. The system treats xbd0 as the boot device	dom0 on domain creation. The system treats xbd0 as the boot device
without needing explicit configuration.	without needing explicit configuration.

	There is not type line; that implicitly defines a pv domU.

By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note	By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
that "xl create" takes the name of a config file, while other commands	that "xl create" takes the name of a config file, while other commands
take the name of a domain.	take the name of a domain.
Line 339 equivalent to pushing the power button;	Line 369 equivalent to pushing the power button;
power-press event and do a clean shutdown. Shutting down the dom0	power-press event and do a clean shutdown. Shutting down the dom0
will trigger controlled shutdowns of all configured domUs.	will trigger controlled shutdowns of all configured domUs.

CPU and memory	## CPU and memory
--------------

A domain is provided with some number of vcpus, up to the number	A domain is provided with some number of vcpus, up to the number
of CPUs seen by the hypervisor. For a domU, it is controlled	of CPUs seen by the hypervisor. For a domU, it is controlled
Line 354 than the available memory.	Line 383 than the available memory.
Xen also provides a "balloon" driver, which can be used to let domains	Xen also provides a "balloon" driver, which can be used to let domains
use more memory temporarily.	use more memory temporarily.

Virtual disks	## Virtual disks
-------------

In domU config files, the disks are defined as a sequence of 3-tuples:	In domU config files, the disks are defined as a sequence of 3-tuples:

Line 390 Note that NetBSD by default creates only	Line 418 Note that NetBSD by default creates only
than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the	than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
dom0.	dom0.

Note that NetBSD by default creates only xbd[0123]. If you need more	## Virtual Networking
virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.

Virtual Networking
------------------

Xen provides virtual Ethernets, each of which connects the dom0 and a	Xen provides virtual Ethernets, each of which connects the dom0 and a
domU. For each virtual network, there is an interface "xvifN.M" in	domU. For each virtual network, there is an interface "xvifN.M" in
Line 426 The MAC address specified is the one use	Line 450 The MAC address specified is the one use
domain. The interface in dom0 will use this address XOR'd with	domain. The interface in dom0 will use this address XOR'd with
00:00:00:01:00:00. Random MAC addresses are assigned if not given.	00:00:00:01:00:00. Random MAC addresses are assigned if not given.

Starting domains automatically	## Starting domains automatically
------------------------------

To start domains `domU-netbsd` and `domU-linux` at boot and shut them	To start domains `domU-netbsd` and `domU-linux` at boot and shut them
down cleanly on dom0 shutdown, add the following in rc.conf:	down cleanly on dom0 shutdown, add the following in rc.conf:
Line 436 down cleanly on dom0 shutdown, add the f	Line 459 down cleanly on dom0 shutdown, add the f
xendomains="domU-netbsd domU-linux"	xendomains="domU-netbsd domU-linux"
"""]]	"""]]

#Creating a domU	# domU setup for specific systems

Creating domUs is almost entirely independent of operating system. We	Creating domUs is almost entirely independent of operating system. We
have already presented the basics of config files. Note that you must	have already presented the basics of config files in the previous system.
have already completed the dom0 setup so that "xl list" works.

Creating a NetBSD domU	Of course, this section presumes that you have a working dom0.
----------------------
	## Creating a NetBSD PV domU

See the earlier config file, and adjust memory. Decide on how much	See the earlier config file, and adjust memory. Decide on how much
storage you will provide, and prepare it (file or LVM).	storage you will provide, and prepare it (file or LVM).
Line 452 While the kernel will be obtained from t	Line 475 While the kernel will be obtained from t
file should be present in the domU as /netbsd so that tools like	file should be present in the domU as /netbsd so that tools like
savecore(8) can work. (This is helpful but not necessary.)	savecore(8) can work. (This is helpful but not necessary.)

The kernel must be specifically for Xen and for use as a domU. The	The kernel must be specifically built for Xen, to use PV interfacesas
i386 and amd64 provide the following kernels:	a domU. NetBSD release builds provide the following kernels:

i386 XEN3PAE_DOMU	i386 XEN3PAE_DOMU
amd64 XEN3_DOMU	amd64 XEN3_DOMU

This will boot NetBSD, but this is not that useful if the disk is	This will boot NetBSD, but this is not that useful if the disk is
empty. One approach is to unpack sets onto the disk outside of xen	empty. One approach is to unpack sets onto the disk outside of Xen
(by mounting it, just as you would prepare a physical disk for a	(by mounting it, just as you would prepare a physical disk for a
system you can't run the installer on).	system you can't run the installer on).

Line 479 line should be used in the config file.	Line 502 line should be used in the config file.
After booting the domain, the option to install via CDROM may be	After booting the domain, the option to install via CDROM may be
selected. The CDROM device should be changed to `xbd1d`.	selected. The CDROM device should be changed to `xbd1d`.

Once done installing, "halt -p" the new domain (don't reboot or halt,	Once done installing, "halt -p" the new domain (don't reboot or halt:
it would reload the INSTALL_XEN3_DOMU kernel even if you changed the	it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
config file), switch the config file back to the XEN3_DOMU kernel,	config file), switch the config file back to the XEN3_DOMU kernel,
and start the new domain again. Now it should be able to use "root on	and start the new domain again. Now it should be able to use "root on
xbd0a" and you should have a, functional NetBSD domU.	xbd0a" and you should have a functional NetBSD domU.

TODO: check if this is still accurate.	TODO: check if this is still accurate.
When the new domain is booting you'll see some warnings about wscons	When the new domain is booting you'll see some warnings about wscons
Line 504 It is also desirable to add	Line 527 It is also desirable to add
powerd=YES	powerd=YES

in rc.conf. This way, the domain will be properly shut down if	in rc.conf. This way, the domain will be properly shut down if
`xm shutdown -R` or `xm shutdown -H` is used on the dom0.	`xl shutdown -R` or `xl shutdown -H` is used on the dom0.
	\todo Check the translation to xl.

It is not strictly necessary to have a kernel (as /netbsd) in the domU	It is not strictly necessary to have a kernel (as /netbsd) in the domU
file system. However, various programs (e.g. netstat) will use that	file system. However, various programs (e.g. netstat) will use that
Line 514 not really a Xen-specific issue, but bec	Line 538 not really a Xen-specific issue, but bec
obtained from the dom0, it is far more likely to be out of sync or	obtained from the dom0, it is far more likely to be out of sync or
missing with Xen.)	missing with Xen.)

Creating a Linux domU	Note that NetBSD by default creates only xbd[0123]. If you need more
---------------------	virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.

	## Creating a Linux domU

Creating unprivileged Linux domains isn't much different from	Creating unprivileged Linux domains isn't much different from
unprivileged NetBSD domains, but there are some details to know.	unprivileged NetBSD domains, but there are some details to know.
Line 558 To get the Linux console right, you need	Line 584 To get the Linux console right, you need
to your configuration since not all Linux distributions auto-attach a	to your configuration since not all Linux distributions auto-attach a
tty to the xen console.	tty to the xen console.

Creating a Solaris domU	## Creating a NetBSD HVM domU
-----------------------
	Use type='hmv', probably. Use a GENERIC kernel within the disk image.

	## Creating a NetBSD PVH domU

	Use type='pvh'.

	\todo Explain where the kernel comes from.


	## Creating a Solaris domU

See possibly outdated	See possibly outdated
[Solaris domU instructions](/ports/xen/howto-solaris/).	[Solaris domU instructions](/ports/xen/howto-solaris/).


PCI passthrough: Using PCI devices in guest domains	## PCI passthrough: Using PCI devices in guest domains
---------------------------------------------------
	NB: PCI passthrough only works on some Xen versions and as of 2020 it
	is not clear that it works on any version in pkgsrc. Reports
	confirming or denying this notion should be sent to port-xen@.

The dom0 can give other domains access to selected PCI	The dom0 can give other domains access to selected PCI
devices. This can allow, for example, a non-privileged domain to have	devices. This can allow, for example, a non-privileged domain to have
Line 635 note that only the "xpci" lines are unus	Line 674 note that only the "xpci" lines are unus
cd* at scsibus? target ? lun ? # SCSI CD-ROM drives	cd* at scsibus? target ? lun ? # SCSI CD-ROM drives


#NetBSD as a domU in a VPS	# Miscellaneous Information

	## Nesting under Linux KVM

	It is possible to run a Xen and a NetBSD dom0 under Linux KVM. One
	can enable virtio in the dom0 for greater speed.

	## Other nesting

	In theory, any full emulation should be able to run Xen and a NetBSD
	dom0. The HOWTO does not currently have information about Xen XVM
	mode, nvmm, qemu, Virtualbox, etc.

	## NetBSD 5 as domU

	[NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
	(However, NetBSD 5 systems should be updated to a supported version.)

	# NetBSD as a domU in a VPS

The bulk of the HOWTO is about using NetBSD as a dom0 on your own	The bulk of the HOWTO is about using NetBSD as a dom0 on your own
hardware. This section explains how to deal with Xen in a domU as a	hardware. This section explains how to deal with Xen in a domU as a
Line 662 A second issue is multiple CPUs. With N	Line 719 A second issue is multiple CPUs. With N
multiple vcpus, and it is typical for VPS providers to enable multiple	multiple vcpus, and it is typical for VPS providers to enable multiple
CPUs for NetBSD domUs.	CPUs for NetBSD domUs.

pvgrub	## Complexities due to Xen changes
------
	Xen has many security advisories and people running Xen systems make
	different choices.

	### stub domains

	Some (Linux only?) dom0 systems use something called "stub domains" to
	isolate qemu from the dom0 system, as a security and reliabilty
	mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
	ends up using PIO for disks rather than DMA. Of course, all of this
	is emulated, but emulated PIO is unusably slow. This problem is not
	currently understood.

	### Grant tables

	There are multiple versions of using grant tables, and some security
	advisories have suggested disabling some versions. Some versions of
	NetBSD apparently only use specific versions and this can lead to
	"NetBSD current doesn't run on hosting provider X" situations.

	\todo Explain better.

	## Boot methods

	### pvgrub

pvgrub is a version of grub that uses PV operations instead of BIOS	pvgrub is a version of grub that uses PV operations instead of BIOS
calls. It is booted from the dom0 as the domU kernel, and then reads	calls. It is booted from the dom0 as the domU kernel, and then reads
Line 688 partition for the kernel with the intent	Line 769 partition for the kernel with the intent
which leads to /netbsd not being the actual kernel. One must remember	which leads to /netbsd not being the actual kernel. One must remember
to update the special boot partition.	to update the special boot partition.

pygrub	### pygrub
-------

pygrub runs in the dom0 and looks into the domU file system. This	pygrub runs in the dom0 and looks into the domU file system. This
implies that the domU must have a kernel in a file system in a format	implies that the domU must have a kernel in a file system in a format
Line 703 historical DomU images using it still wo	Line 783 historical DomU images using it still wo
As of 2014, pygrub seems to be of mostly historical	As of 2014, pygrub seems to be of mostly historical
interest. New DomUs should use pvgrub.	interest. New DomUs should use pvgrub.

Amazon	## Specific Providers
------
	### Amazon

See the [Amazon EC2 page](/amazon_ec2/).	See the [Amazon EC2 page](/amazon_ec2/).

CVSweb for NetBSD wikisrc <wikimaster@NetBSD.org> software: FreeBSD-CVSweb

Removed from v.1.170
changed lines
	Added in v.1.189