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version 1.177, 2020/11/13 20:41:56	version 1.180, 2020/11/15 14:31:58
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 guests; see [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM) and [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2)_Domu) for upstream documentation.	Xen supports different styles of guests; see [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM) and [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu) for upstream documentation.

[[!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 (domU)	PVHVM \|current-only (domU)
PVHv2 \|current-only (domU, dom0 not yet)	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
Line 29 The dom0 runs qemu to emulate hardware.	Line 29 The dom0 runs qemu to emulate hardware.
In PVHVM mode, the guest runs as HVM, but additionally can use PV	In PVHVM mode, the guest runs as HVM, but additionally can use PV
drivers for efficiency.	drivers for efficiency.

In PVHv2H mode, operation is similar to PVHVM, except that qemu is not	There have been two PVH modes: original PVH and PVHv2. Original PVH
run and thus the PV interfaces for console, disks, networking are the	was based on PV mode and is no longer relevant at all. PVHv2 is
only way to access these resources.	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.

At boot, the dom0 kernel is loaded as a module with Xen as the kernel.	At 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
Line 105 just as you would if you were not using	Line 109 just as you would if you were not using
Installation of Xen	Installation of Xen
-------------------	-------------------

We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as	We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.	dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.

Once this is done, install the Xen kernel itself:	Once this is done, install the Xen kernel itself:
Line 145 itself uses (in this case, the serial po	Line 149 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.

Line 196 this will get fixed any time soon.	Line 200 this will get fixed any time soon.
anita (for testing NetBSD)	anita (for testing NetBSD)
--------------------------	--------------------------

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

Line 427 down cleanly on dom0 shutdown, add the f	Line 431 down cleanly on dom0 shutdown, add the f
xendomains="domU-netbsd domU-linux"	xendomains="domU-netbsd domU-linux"
"""]]	"""]]

#Creating a domU	# Creating a domU

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. Note that you must
have already completed the dom0 setup so that "xl list" works.	have already completed the dom0 setup so that "xl list" works.

Creating a NetBSD domU	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 549 To get the Linux console right, you need	Line 553 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 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	Creating a Solaris domU
-----------------------	-----------------------

Line 559 See possibly outdated	Line 574 See possibly outdated
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
access to a physical network interface or disk controller. However,	access to a physical network interface or disk controller. However,
Line 660 A second issue is multiple CPUs. With N	Line 679 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.

	## 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.

pvgrub	pvgrub
------	------

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