1: [[!meta title="Xen HowTo"]]
3: Xen is a Type 1 hypervisor which supports running multiple guest operating
4: systems on a single physical machine. One uses the Xen kernel to control the
5: CPU, memory and console, a dom0 operating system which mediates access to
6: other hardware (e.g., disks, network, USB), and one or more domU operating
7: systems which operate in an unprivileged virtualized environment. IO requests
8: from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
11: This HOWTO presumes a basic familiarity with the Xen system
12: architecture, with installing NetBSD on amd64 hardware, and with
13: installing software from pkgsrc. See also the [Xen
18: # Overview
20: The basic concept of Xen is that the hypervisor (xenkernel) runs on
21: the hardware, and runs a privileged domain ("dom0") that can access
22: disks/networking/etc. One then runs additonal unprivileged domains
23: (each a "domU"), presumably to do something useful.
25: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
26: xen itself). It also addresses how to run domUs in that environment,
27: and how to deal with having a domU in a Xen environment run by someone
28: else and/or not running NetBSD.
30: There are many choices one can make; the HOWTO recommends the standard
31: approach and limits discussion of alternatives in many cases.
33: ## Guest Styles
35: Xen supports different styles of guests.
37: [[!table data="""
38: Style of guest |Supported by NetBSD
39: PV |Yes (dom0, domU)
40: HVM |Yes (domU)
41: PVHVM |current-only (domU)
42: PVH |current-only (domU, dom0 not yet)
45: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
46: hardware directly, but instead makes hypercalls to the hypervisor; PV
47: guests must be specifically coded for Xen.
48: See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
50: In HVM mode, no guest modification is required; however, hardware
51: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
52: The dom0 runs qemu to emulate hardware.
54: In PVHVM mode, the guest runs as HVM, but additionally can use PV
55: drivers for efficiency.
56: See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
58: There have been two PVH modes: original PVH and PVHv2. Original PVH
59: was based on PV mode and is no longer relevant at all. PVHv2 is
60: basically lightweight HVM with PV drivers. A critical feature of it
61: is that qemu is not needed; the hypervisor can do the emulation that
62: is required. Thus, a dom0 can be PVHv2.
63: The source code uses PVH and config files use pvh; this refers to PVHv2.
64: See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
66: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
67: The dom0 can start one or more domUs. (Booting is explained in detail
68: in the dom0 section.)
70: ## CPU Architecture
72: Xen runs on x86_64 hardware (the NetBSD amd64 port).
74: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
76: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
78: The domU can be i386PAE or amd64.
79: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
81: ## Xen Versions
83: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
84: xenkernel and xentools. We will refer only to the kernel versions,
85: but note that both packages must be installed together and must have
86: matching versions.
88: Versions available in pkgsrc:
90: [[!table data="""
91: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
92: 4.11 |xenkernel411 |x86_64 |No
93: 4.13 |xenkernel413 |x86_64 |No
96: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
98: Older Xen had a python-based management tool called xm, now replaced
99: by xl.
101: ## NetBSD versions
103: Xen has been supported in NetBSD for a long time, at least since 2005.
104: Initially Xen was PV only.
106: NetBSD 8 and up support PV and HVM modes.
108: Support for PVHVM and PVH is available only in NetBSD-current.
110: NetBSD up to and including NetBSD 9 as a dom0 does not run SMP,
111: because some drivers are not yet safe for this. NetBSD-current
112: supports SMP in dom0.
114: NetBSD, when run as a domU, can and does typically run SMP.
116: Note that while Xen 4.13 is current, the kernel support is still
117: called XEN3, because the hypercall interface has not changed
120: # Creating a NetBSD dom0
122: In order to install a NetBSD as a dom0, one first installs a normal
123: NetBSD system, and then pivot the install to a dom0 install by
124: changing the kernel and boot configuration.
126: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
127: 512M it worked reliably. This does not make sense, but if you see
128: "not ELF" after Xen boots, try increasing dom0 RAM.
130: ## Installation of NetBSD
132: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
133: using Xen. Therefore, use the most recent release, or a build from
134: the most recent stable branch. Alternatively, use -current, being
135: mindful of all the usual caveats of lower stability of current, and
136: likely a bit more so.
138: ## Installation of Xen
140: ### Building Xen
142: Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
143: Therefore, choose 4.13.
144: In the dom0, install xenkernel413 and xentools413 from pkgsrc.
146: Once this is done, copy the Xen kernel from where pkgsrc puts it to
147: where the boot process will be able to find it:
149: [[!template id=programlisting text="""
150: # cp -p /usr/pkg/xen413-kernel/xen.gz /
153: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
154: kernel can either be taken from a local release build.sh run, compiled
155: manually, or downloaded from the NetBSD FTP, for example at:
157: [[!template id=programlisting text="""
161: ### Configuring booting
163: Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen:
165: [[!template id=filecontent name="/boot.cfg" text="""
166: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
167: menu=Xen single user:load /netbsd-XEN3_DOM0.gz console=pc -s;multiboot /xen.gz dom0_mem=512M
170: This specifies that the dom0 should have 512MB of ram, leaving the rest
171: to be allocated for domUs.
173: NB: This says add, not replace, so that you will be able to more
174: easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may
175: want to set it as default. It is highly likely that you will have
176: trouble at some point, and keeping an up-to-date GENERIC for use in
177: fixing problems is the standard prudent approach.
179: ### Console selection
181: See boot_console(8). Understand that you should start from a place of
182: having console setup correct for booting GENERIC before trying to
183: configure Xen.
185: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
186: equivalent, and this is passed on to /boot (where one typically does
187: not set the console). This configuration of bootxx_ffsv1 should also
188: be in place for Xen systems, to allow seeing messages from /boot and
189: use of a keyboard to select a line from the menu. And, one should
190: have a working boot path to GENERIC for rescue situations.
192: With GENERIC, the boot options are passed on to /netbsd, but there is
193: currently no mechanism to pass these via multiboot to the hypervisor.
194: Thus, in addition to configuring the console in the boot blocks, one
195: must also configure it for Xen.
197: By default, the hypervisor (Xen itself) will use some sort of vga
198: device as the console, much like GENERIC uses by default. The vga
199: console is relinquished at the conclusion of hypervisor boot, before
200: the dom0 is started.
202: \todo Explain if there is any notion of input to the Xen console;
203: there is something about 3 CTRL-As in a row. Perhaps this is about
204: the serial console which is not relinquished?
206: The hypervisor can be configured to use a serial port console, e.g.
207: [[!template id=filecontent name="/boot.cfg" text="""
208: menu=Xen:losad /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
210: This exampulee uses the first serial port (Xen counts from 1; this is
211: what NetBSD would call com0), and sets speed and parity. (The dom0 is
212: then configured to use the same serial port in this example.)
214: One also configures the console for the dom0. While one might expect
215: console=pc to be default, following behavior of GENERIC, a hasty read
216: of the code suggests there is no default and booting without a
217: selected console might lead to a panic. Also, there is merit in
218: explicit configuration. Therefore the standard approach is to place
219: console=pc as part of the load statement for the dom0 kernel, or
220: alternatively console=com0.
222: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
223: exist), but this is not used as a console. It is used to obtain the
224: messages from the hypervisor's console; run `xl dmesg` to see them.
226: ### Tuning
228: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
229: to force only one vcpu to be provided (since NetBSD dom0 can't use
230: more) and to pin that vcpu to a physical CPU. Xen has
231: [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
232: and other than dom0 memory and max_vcpus, they are generally not
234: \todo Revisit this advice with current.
235: \todo Explain if anyone has ever actually measured that this helps.
237: ### rc.conf
239: Ensure that the boot scripts installed in
240: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
241: have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
242: but a normal part of pkgsrc usage.)
244: Set `xencommons=YES` in rc.conf:
246: [[!template id=filecontent name="/etc/rc.conf" text="""
250: \todo Recommend for/against xen-watchdog.
252: ### Testing
254: Now, reboot so that you are running a DOM0 kernel under Xen, rather
255: than GENERIC without Xen.
257: Once the reboot is done, use `xl` to inspect Xen's boot messages,
258: available resources, and running domains. For example:
260: [[!template id=programlisting text="""
261: # xl dmesg
262: ... xen's boot info ...
263: # xl info
264: ... available memory, etc ...
265: # xl list
266: Name Id Mem(MB) CPU State Time(s) Console
267: Domain-0 0 64 0 r---- 58.1
270: Xen logs will be in /var/log/xen.
272: ### Issues with xencommons
274: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
275: domUs. It does not currently work to stop and start xenstored.
276: Certainly all domUs should be shutdown first, following the sort order
277: of the rc.d scripts. However, the dom0 sets up state with xenstored,
278: and is not notified when xenstored exits, leading to not recreating
279: the state when the new xenstored starts. Until there's a mechanism to
280: make this work, one should not expect to be able to restart xenstored
281: (and thus xencommons). There is currently no reason to expect that
282: this will get fixed any time soon.
283: \todo Confirm if this is still true in 2020.
285: ## Xen-specific NetBSD issues
287: There are (at least) two additional things different about NetBSD as a
288: dom0 kernel compared to hardware.
290: One is that through NetBSD 9 the module ABI is different because some
291: of the #defines change, so there are separate sets of modules in
292: /stand. In NetBSD-current, there is only one set of modules.
294: The other difference is that XEN3_DOM0 does not have exactly the same
295: options as GENERIC. While it is debatable whether or not this is a
296: bug, users should be aware of this and can simply add missing config
297: items if desired.
299: Finally, there have been occasional reports of trouble with X11
300: servers in NetBSD as a dom0.
302: ## Updating Xen in a dom0
304: Basically, update the xenkernel and xentools packages and copy the new
305: Xen kernel into place, and reboot. This procedure should be usable to
306: update to a new Xen release, but the reader is reminded that having a
307: non-Xen boot methods was recommended earlier.
309: ## Updating NetBSD in a dom0
311: This is just like updating NetBSD on bare hardware, assuming the new
312: version supports the version of Xen you are running. Generally, one
313: replaces the kernel and reboots, and then overlays userland binaries
314: and adjusts `/etc`.
316: Note that one should update both the non-Xen kernel typically used for
317: rescue purposes, as well as the DOM0 kernel used with Xen.
319: ## anita (for testing NetBSD)
321: With a NetBSD dom0, even without any domUs, one should be able to run
322: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
323: root, because anita must create a domU):
325: [[!template id=programlisting text="""
326: anita --vmm=xl test file:///usr/obj/i386/
329: # Unprivileged domains (domU)
331: This section describes general concepts about domUs. It does not
332: address specific domU operating systems or how to install them. The
333: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
334: typically named so that the file name, domU name and the domU's host
335: name match.
337: The domU is provided with CPU and memory by Xen, configured by the
338: dom0. The domU is provided with disk and network by the dom0,
339: mediated by Xen, and configured in the dom0.
341: Entropy in domUs can be an issue; physical disks and network are on
342: the dom0. NetBSD's /dev/random system works, but is often challenged.
344: ## Config files
346: See /usr/pkg/share/examples/xen/xlexample*
347: for a small number of well-commented examples, mostly for running
350: The following is an example minimal domain configuration file. The domU
351: serves as a network file server.
353: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
354: name = "domU-id"
355: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
356: memory = 1024
357: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
358: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
359: 'file:/n0/xen/foo-wd1,0x1,w' ]
362: The domain will have name given in the `name` setting. The kernel has the
363: host/domU name in it, so that on the dom0 one can update the various
364: domUs independently. The `vif` line causes an interface to be provided,
365: with a specific mac address (do not reuse MAC addresses!), in bridge
366: mode. Two disks are provided, and they are both writable; the bits
367: are stored in files and Xen attaches them to a vnd(4) device in the
368: dom0 on domain creation. The system treats xbd0 as the boot device
369: without needing explicit configuration.
371: There is not type line; that implicitly defines a pv domU.
373: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
374: that "xl create" takes the name of a config file, while other commands
375: take the name of a domain.
377: Examples of commands:
379: [[!template id=programlisting text="""
380: xl create /usr/pkg/etc/xen/foo
381: xl console domU-id
382: xl create -c /usr/pkg/etc/xen/foo
383: xl shutdown domU-id
384: xl list
387: Typing `^]` will exit the console session. Shutting down a domain is
388: equivalent to pushing the power button; a NetBSD domU will receive a
389: power-press event and do a clean shutdown. Shutting down the dom0
390: will trigger controlled shutdowns of all configured domUs.
392: ## CPU and memory
394: A domain is provided with some number of vcpus, up to the number
395: of CPUs seen by the hypervisor. For a domU, it is controlled
396: from the config file by the "vcpus = N" directive.
398: A domain is provided with memory; this is controlled in the config
399: file by "memory = N" (in megabytes). In the straightforward case, the
400: sum of the the memory allocated to the dom0 and all domUs must be less
401: than the available memory.
403: Xen also provides a "balloon" driver, which can be used to let domains
404: use more memory temporarily.
406: ## Virtual disks
408: In domU config files, the disks are defined as a sequence of 3-tuples:
410: * The first element is "method:/path/to/disk". Common methods are
411: "file:" for a file-backed vnd, and "phy:" for something that is already
412: a device, such as an LVM logical volume.
414: * The second element is an artifact of how virtual disks are passed to
415: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
416: are given a device name to associate with the disk, and values like
417: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
418: as xbd0, the second as xbd1, and so on. However, xl demands a
419: second argument. The name given is converted to a major/minor by
420: calling stat(2) on the name in /dev and this is passed to the domU.
421: In the general case, the dom0 and domU can be different operating
422: systems, and it is an unwarranted assumption that they have consistent
423: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
424: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
425: for the second works fine and avoids this issue. For a GNU/Linux
426: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
429: * The third element is "w" for writable disks, and "r" for read-only
433: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
434: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
437: Note that NetBSD by default creates only vnd. If you need more
438: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
441: ## Virtual Networking
443: Xen provides virtual Ethernets, each of which connects the dom0 and a
444: domU. For each virtual network, there is an interface "xvifN.M" in
445: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
446: The interfaces behave as if there is an Ethernet with two
447: adapters connected. From this primitive, one can construct various
448: configurations. We focus on two common and useful cases for which
449: there are existing scripts: bridging and NAT.
451: With bridging (in the example above), the domU perceives itself to be
452: on the same network as the dom0. For server virtualization, this is
453: usually best. Bridging is accomplished by creating a bridge(4) device
454: and adding the dom0's physical interface and the various xvifN.0
455: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
456: config file. The bridge must be set up already in the dom0; an
457: example /etc/ifconfig.bridge0 is:
459: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
462: !brconfig bridge0 add wm0
465: With NAT, the domU perceives itself to be behind a NAT running on the
466: dom0. This is often appropriate when running Xen on a workstation.
467: TODO: NAT appears to be configured by "vif = [ '' ]".
469: The MAC address specified is the one used for the interface in the new
470: domain. The interface in dom0 will use this address XOR'd with
471: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
473: ## Starting domains automatically
475: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
476: down cleanly on dom0 shutdown, add the following in rc.conf:
478: [[!template id=filecontent name="/etc/rc.conf" text="""
479: xendomains="domU-netbsd domU-linux"
482: # domU setup for specific systems
484: Creating domUs is almost entirely independent of operating system. We
485: have already presented the basics of config files in the previous system.
487: Of course, this section presumes that you have a working dom0.
489: ## Creating a NetBSD PV domU
491: See the earlier config file, and adjust memory. Decide on how much
492: storage you will provide, and prepare it (file or LVM).
494: While the kernel will be obtained from the dom0 file system, the same
495: file should be present in the domU as /netbsd so that tools like
496: savecore(8) can work. (This is helpful but not necessary.)
498: The kernel must be specifically built for Xen, to use PV interfacesas
499: a domU. NetBSD release builds provide the following kernels:
501: i386 XEN3PAE_DOMU
502: amd64 XEN3_DOMU
504: This will boot NetBSD, but this is not that useful if the disk is
505: empty. One approach is to unpack sets onto the disk outside of Xen
506: (by mounting it, just as you would prepare a physical disk for a
507: system you can't run the installer on).
509: A second approach is to run an INSTALL kernel, which has a miniroot
510: and can load sets from the network. To do this, copy the INSTALL
511: kernel to / and change the kernel line in the config file to:
513: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
515: Then, start the domain as "xl create -c configfile".
517: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
518: line should be used in the config file.
520: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
522: After booting the domain, the option to install via CDROM may be
523: selected. The CDROM device should be changed to `xbd1d`.
525: Once done installing, "halt -p" the new domain (don't reboot or halt:
526: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
527: config file), switch the config file back to the XEN3_DOMU kernel,
528: and start the new domain again. Now it should be able to use "root on
529: xbd0a" and you should have a functional NetBSD domU.
531: TODO: check if this is still accurate.
532: When the new domain is booting you'll see some warnings about *wscons*
533: and the pseudo-terminals. These can be fixed by editing the files
534: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
535: `/etc/ttys`, except *console*, like this:
537: console "/usr/libexec/getty Pc" vt100 on secure
538: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
539: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
540: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
541: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
543: Finally, all screens must be commented out from `/etc/wscons.conf`.
545: One should also run `powerd` in a domU, but this should not need
546: configuring. With powerd, the domain will run a controlled shutdown
547: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
548: receiving a synthetic `power button pressed` signal. In 9 and
549: current, `powerd` is run by default under Xen kernels (or if ACPI is
550: present), and it can be added to rc.conf if not.
552: It is not strictly necessary to have a kernel (as /netbsd) in the domU
553: file system. However, various programs (e.g. netstat) will use that
554: kernel to look up symbols to read from kernel virtual memory. If
555: /netbsd is not the running kernel, those lookups will fail. (This is
556: not really a Xen-specific issue, but because the domU kernel is
557: obtained from the dom0, it is far more likely to be out of sync or
558: missing with Xen.)
560: Note that NetBSD by default creates only xbd. If you need more
561: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
563: ## Creating a Linux domU
565: Creating unprivileged Linux domains isn't much different from
566: unprivileged NetBSD domains, but there are some details to know.
568: First, the second parameter passed to the disk declaration (the '0x1' in
569: the example below)
571: disk = [ 'phy:/dev/wd0e,0x1,w' ]
573: does matter to Linux. It wants a Linux device number here (e.g. 0x300
574: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
575: So, hda1 which has major 3 and minor 1 on a Linux system will have
576: device number 0x301. Alternatively, devices names can be used (hda,
577: hdb, ...) as xentools has a table to map these names to devices
578: numbers. To export a partition to a Linux guest we can use:
580: disk = [ 'phy:/dev/wd0e,0x300,w' ]
581: root = "/dev/hda1 ro"
583: and it will appear as /dev/hda on the Linux system, and be used as root
586: To install the Linux system on the partition to be exported to the
587: guest domain, the following method can be used: install
588: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
589: that will be the root partition of your Linux domain, and mount it.
590: Then copy the files from a working Linux system, make adjustments in
591: `/etc` (fstab, network config). It should also be possible to extract
592: binary packages such as .rpm or .deb directly to the mounted partition
593: using the appropriate tool, possibly running under NetBSD's Linux
594: emulation. Once the file system has been populated, umount it. If
595: desirable, the file system can be converted to ext3 using tune2fs -j.
596: It should now be possible to boot the Linux guest domain, using one of
597: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
599: To get the Linux console right, you need to add:
601: extra = "xencons=tty1"
603: to your configuration since not all Linux distributions auto-attach a
604: tty to the xen console.
606: ## Creating a NetBSD HVM domU
608: Use type='hmv', probably. Use a GENERIC kernel within the disk image.
610: ## Creating a NetBSD PVH domU
612: Use type='pvh'.
614: \todo Explain where the kernel comes from.
616: ## Creating a Solaris domU
618: See possibly outdated
619: [Solaris domU instructions](/ports/xen/howto-solaris/).
621: ## PCI passthrough: Using PCI devices in guest domains
623: NB: PCI passthrough only works on some Xen versions and as of 2020 it
624: is not clear that it works on any version in pkgsrc. Reports
625: confirming or denying this notion should be sent to port-xen@.
627: The dom0 can give other domains access to selected PCI
628: devices. This can allow, for example, a non-privileged domain to have
629: access to a physical network interface or disk controller. However,
630: keep in mind that giving a domain access to a PCI device most likely
631: will give the domain read/write access to the whole physical memory,
632: as PCs don't have an IOMMU to restrict memory access to DMA-capable
633: device. Also, it's not possible to export ISA devices to non-dom0
634: domains, which means that the primary VGA adapter can't be exported.
635: A guest domain trying to access the VGA registers will panic.
637: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
638: not been ported to later versions at this time.
640: For a PCI device to be exported to a domU, is has to be attached to
641: the "pciback" driver in dom0. Devices passed to the dom0 via the
642: pciback.hide boot parameter will attach to "pciback" instead of the
643: usual driver. The list of devices is specified as "(bus:dev.func)",
644: where bus and dev are 2-digit hexadecimal numbers, and func a
645: single-digit number:
649: pciback devices should show up in the dom0's boot messages, and the
650: devices should be listed in the `/kern/xen/pci` directory.
652: PCI devices to be exported to a domU are listed in the "pci" array of
653: the domU's config file, with the format "0000:bus:dev.func".
655: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
657: In the domU an "xpci" device will show up, to which one or more pci
658: buses will attach. Then the PCI drivers will attach to PCI buses as
659: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
660: or any PCI drivers built in by default; you have to build your own
661: kernel to use PCI devices in a domU. Here's a kernel config example;
662: note that only the "xpci" lines are unusual.
664: include "arch/i386/conf/XEN3_DOMU"
666: # Add support for PCI buses to the XEN3_DOMU kernel
667: xpci* at xenbus ?
668: pci* at xpci ?
670: # PCI USB controllers
671: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
673: # USB bus support
674: usb* at uhci?
676: # USB Hubs
677: uhub* at usb?
678: uhub* at uhub? port ? configuration ? interface ?
680: # USB Mass Storage
681: umass* at uhub? port ? configuration ? interface ?
682: wd* at umass?
683: # SCSI controllers
684: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
686: # SCSI bus support (for both ahc and umass)
687: scsibus* at scsi?
689: # SCSI devices
690: sd* at scsibus? target ? lun ? # SCSI disk drives
691: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
694: # Miscellaneous Information
696: ## Nesting under Linux KVM
698: It is possible to run a Xen and a NetBSD dom0 under Linux KVM. One
699: can enable virtio in the dom0 for greater speed.
701: ## Other nesting
703: In theory, any full emulation should be able to run Xen and a NetBSD
704: dom0. The HOWTO does not currently have information about Xen XVM
705: mode, nvmm, qemu, Virtualbox, etc.
707: ## NetBSD 5 as domU
709: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
710: (However, NetBSD 5 systems should be updated to a supported version.)
712: # NetBSD as a domU in a VPS
714: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
715: hardware. This section explains how to deal with Xen in a domU as a
716: virtual private server where you do not control or have access to the
717: dom0. This is not intended to be an exhaustive list of VPS providers;
718: only a few are mentioned that specifically support NetBSD.
720: VPS operators provide varying degrees of access and mechanisms for
721: configuration. The big issue is usually how one controls which kernel
722: is booted, because the kernel is nominally in the dom0 file system (to
723: which VPS users do not normally have access). A second issue is how
724: to install NetBSD.
725: A VPS user may want to compile a kernel for security updates, to run
726: npf, run IPsec, or any other reason why someone would want to change
727: their kernel.
729: One approach is to have an administrative interface to upload a kernel,
730: or to select from a prepopulated list. Other approaches are pygrub
731: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
732: kernel from the domU file system. This is closer to a regular physical
733: computer, where someone who controls a machine can replace the kernel.
735: A second issue is multiple CPUs. With NetBSD 6, domUs support
736: multiple vcpus, and it is typical for VPS providers to enable multiple
737: CPUs for NetBSD domUs.
739: ## Complexities due to Xen changes
741: Xen has many security advisories and people running Xen systems make
742: different choices.
744: ### stub domains
746: Some (Linux only?) dom0 systems use something called "stub domains" to
747: isolate qemu from the dom0 system, as a security and reliabilty
748: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
749: ends up using PIO for disks rather than DMA. Of course, all of this
750: is emulated, but emulated PIO is unusably slow. This problem is not
751: currently understood.
753: ### Grant tables
755: There are multiple versions of using grant tables, and some security
756: advisories have suggested disabling some versions. Some versions of
757: NetBSD apparently only use specific versions and this can lead to
758: "NetBSD current doesn't run on hosting provider X" situations.
760: \todo Explain better.
762: ## Boot methods
764: ### pvgrub
766: pvgrub is a version of grub that uses PV operations instead of BIOS
767: calls. It is booted from the dom0 as the domU kernel, and then reads
768: /grub/menu.lst and loads a kernel from the domU file system.
770: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
771: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
772: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
773: page](http://www.panix.com/v-colo/grub.html), which describes only
774: Linux but should be updated to cover NetBSD :-).
776: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
777: their own kernel. See then [prgmr.com NetBSD
779: (which is in need of updating).
781: It appears that [grub's FFS
783: does not support all aspects of modern FFS, but there are also reports
784: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
785: partition for the kernel with the intent that grub can understand it,
786: which leads to /netbsd not being the actual kernel. One must remember
787: to update the special boot partition.
789: ### pygrub
791: pygrub runs in the dom0 and looks into the domU file system. This
792: implies that the domU must have a kernel in a file system in a format
793: known to pygrub.
795: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
796: and is inherently less secure than pvgrub due to running inside dom0. For both these
797: reasons, pygrub should not be used, and is only still present so that
798: historical DomU images using it still work.
800: As of 2014, pygrub seems to be of mostly historical
801: interest. New DomUs should use pvgrub.
803: ## Specific Providers
805: ### Amazon
807: See the [Amazon EC2 page](/amazon_ec2/).
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