1: [[!meta title="Xen Status and HowTo"]]
2:
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
9: fulfilled.
10:
11: This document provides status on what Xen things work on NetBSD
12: (upstream documentation might say something works if it works on some
13: particular Linux system).
14:
15: This document is also a HOWTO that presumes a basic familiarity with
16: the Xen system architecture, with installing NetBSD on amd64 hardware,
17: and with installing software from pkgsrc. See also the [Xen
18: website](http://www.xenproject.org/).
19:
20: If this document says that something works, and you find that it does
21: not, it is best to ask on port-xen and if you are correct to file a
22: PR.
23:
24: [[!toc]]
25:
26: # Overview
27:
28: The basic concept of Xen is that the hypervisor (xenkernel) runs on
29: the hardware, and runs a privileged domain ("dom0") that can access
30: disks/networking/etc. One then runs additional unprivileged domains
31: (each a "domU"), presumably to do something useful.
32:
33: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
34: xen itself). It also addresses how to run domUs in that environment,
35: and how to deal with having a domU in a Xen environment run by someone
36: else and/or not running NetBSD.
37:
38: There are many choices one can make; the HOWTO recommends the standard
39: approach and limits discussion of alternatives in many cases.
40:
41: ## Guest Styles
42:
43: Xen supports different styles of guests. See
44: https://wiki.xenproject.org/wiki/Virtualization_Spectrum for a
45: discussion.
46:
47: This table shows the styles, and if a NetBSD dom0 can run in that
48: style, if a NetBSD dom0 can sypport that style of guest in a domU, and
49: if NetBSD as a domU can support that style.
50:
51: [[!table data="""
52: Style of guest |dom0 can be? |dom0 can support? |domU can be?
53: PV |yes |yes |yes
54: HVM |N/A |yes |yes
55: PVHVM |N/A |yes |current only
56: PVH |not yet |current only |current only
57: """]]
58:
59: In PV (paravirtualized) mode, the guest OS does not attempt to access
60: hardware directly, but instead makes hypercalls to the hypervisor; PV
61: guests must be specifically coded for Xen. See
62: [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
63:
64: In HVM (Hardware Virtual Machine) mode, no guest modification is
65: required. However, hardware support is required, such as VT-x on
66: Intel CPUs and SVM on AMD CPUs to assist with the processor emulation.
67: The dom0 runs qemu to emulate hardware other than the processor. It
68: is therefore non-sensical to have an HVM dom0, because there is no
69: underlying system to provide emulation.
70:
71: In PVHVM mode, the guest runs as HVM, but additionally uses PV
72: drivers for efficiency. Therefore it is non-sensical for to have a
73: PVHVM dom0. See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
74:
75: There have been two PVH modes: original PVH and PVHv2. Original PVH
76: was based on PV mode and is no longer relevant at all. Therefore
77: PVHv2 is written as PVH, here and elsewhere. PVH is basically
78: lightweight HVM with PV drivers. A critical feature of it is that
79: qemu is not needed; the hypervisor can do the emulation that is
80: required. Thus, a dom0 can be PVH. The source code uses PVH and
81: config files use pvh, but NB that this refers to PVHv2. See
82: [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
83:
84: At system boot, the dom0 kernel is loaded as a module with Xen as the
85: kernel. The dom0 can start one or more domUs. (Booting is explained
86: in detail in the dom0 section.)
87:
88: ## CPU Architecture
89:
90: Xen runs on x86_64 hardware (the NetBSD amd64 port).
91:
92: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
93:
94: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
95:
96: The domU can be i386 PAE or amd64.
97: i386 PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
98: However, as of 2021 it is normal to use amd64 as the domU architecture, and use of i386 is dwindling.
99:
100: ## Xen Versions
101:
102: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
103: xenkernel and xentools. We will refer only to the kernel versions,
104: but note that both packages must be installed together and must have
105: matching versions.
106:
107: Versions available in pkgsrc:
108:
109: [[!table data="""
110: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
111: 4.11 |xenkernel411 |x86_64 |No
112: 4.13 |xenkernel413 |x86_64 |No
113: """]]
114:
115: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
116:
117: Older Xen had a python-based management tool called xm; this has been
118: replaced by xl.
119:
120: ## NetBSD versions
121:
122: Xen has been supported in NetBSD for a long time, at least since 2005.
123: Initially Xen was PV only.
124:
125: NetBSD Xen has always supported PV, in both dom0 and domU; for a long
126: time this was the only way. NetBSD >=8 as a dom0 supports HVM mode in
127: domUs.
128:
129: Support for PVHVM and PVH is available only in NetBSD-current; this is
130: currently somewhat experimental, although PVHVM appears reasonably
131: solid.
132:
133: NetBSD up to and including NetBSD 9 as a dom0 cannot safely run SMP.
134: Even if one added "options MULTIPROCESSOR" and configured multiple
135: vcpus, the kernel is likely to crash because of drivers without
136: adequate locking.
137:
138: NetBSD-current supports SMP in dom0, and XEN3_DOM0 includes "options
139: MULTIPROCESSOR".
140:
141: NetBSD (since NetBSD 6), when run as a domU, can run SMP, using
142: multiple CPUs if provided. The XEN3_DOMU kernel is built
143: with "options MULITPROCESSOR".
144:
145: Note that while Xen 4.13 is current, the kernel support is still
146: called XEN3, because the hypercall interface has not changed
147: significantly.
148:
149: # Creating a NetBSD dom0
150:
151: In order to install a NetBSD as a dom0, one first installs a normal
152: NetBSD system, and then pivot the install to a dom0 install by
153: changing the kernel and boot configuration.
154:
155: NB: As of 2021-04, you must arrange to have the system use BIOS boot,
156: not EFI boot.
157:
158: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
159: 512M it worked reliably. This does not make sense, but if you see
160: "not ELF" after Xen boots, try increasing dom0 RAM.
161:
162: ## Installation of NetBSD
163:
164: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
165: using Xen. Therefore, use the most recent release, or a build from
166: the most recent stable branch. Alternatively, use -current, being
167: mindful of all the usual caveats of lower stability of current, and
168: likely a bit more so. Think about how you will provide storage for
169: disk images.
170:
171: ## Installation of Xen
172:
173: ### Building Xen
174:
175: Use the most recent version of Xen in pkgsrc, unless the DESCR says
176: that it is not suitable. Therefore, choose 4.13. In the dom0,
177: install xenkernel413 and xentools413 from pkgsrc.
178:
179: Once this is done, copy the Xen kernel from where pkgsrc puts it to
180: where the boot process will be able to find it:
181:
182: [[!template id=programlisting text="""
183: # cp -p /usr/pkg/xen413-kernel/xen.gz /
184: """]]
185:
186: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
187: kernel can either be taken from a local release build.sh run, compiled
188: manually, or downloaded from the NetBSD FTP, for example at:
189:
190: [[!template id=programlisting text="""
191: ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
192: """]]
193:
194: ### Configuring booting
195:
196: Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen,
197: adjusting for your root filesystem:
198:
199: [[!template id=filecontent name="/boot.cfg" text="""
200: menu=Xen:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc;multiboot /xen.gz dom0_mem=512M
201: menu=Xen single user:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc -s;multiboot /xen.gz dom0_mem=512M
202: """]]
203:
204: This specifies that the dom0 should have 512MB of ram, leaving the rest
205: to be allocated for domUs.
206:
207: NB: This says add, not replace, so that you will be able to more
208: easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may
209: want to set it as default. It is highly likely that you will have
210: trouble at some point, and keeping an up-to-date GENERIC for use in
211: fixing problems is the standard prudent approach.
212:
213: \todo Explain why rndseed is not set with Xen as part of the dom0
214: subconfiguration.
215:
216: Note that you are likely to have to set root= because the boot device
217: from /boot is not passed via Xen to the dom0 kernel. With one disk,
218: it will work, but e.g. plugging in USB disk to a machine with root on
219: wd0a causes boot to fail.
220:
221: Beware that userconf statements must be attached to the dom0 load, and
222: may not be at top-level, because then they would try to configure the
223: hypervisor, if there is a way to pass them via multiboot. It appears
224: that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very
225: early with a heap overflow.
226:
227: ### Console selection
228:
229: See boot_console(8). Understand that you should start from a place of
230: having console setup correct for booting GENERIC before trying to
231: configure Xen.
232:
233: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
234: equivalent, and this is passed on to /boot (where one typically does
235: not set the console). This configuration of bootxx_ffsv1 should also
236: be in place for Xen systems, to allow seeing messages from /boot and
237: use of a keyboard to select a line from the menu. And, one should
238: have a working boot path to GENERIC for rescue situations.
239:
240: With GENERIC, the boot options are passed on to /netbsd, but there is
241: currently no mechanism to pass these via multiboot to the hypervisor.
242: Thus, in addition to configuring the console in the boot blocks, one
243: must also configure it for Xen.
244:
245: By default, the hypervisor (Xen itself) will use some sort of vga
246: device as the console, much like GENERIC uses by default. The vga
247: console is relinquished at the conclusion of hypervisor boot, before
248: the dom0 is started. Xen when using a vga console does not process
249: console input.
250:
251: The hypervisor can be configured to use a serial port console, e.g.
252: [[!template id=filecontent name="/boot.cfg" text="""
253: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
254: """]]
255: This example uses the first serial port (Xen counts from 1; this is
256: what NetBSD would call com0), and sets speed and parity. (The dom0 is
257: then configured to use the same serial port in this example.)
258:
259: With the hypervisor configured for a serial console, it can get input,
260: and there is a notion of passing this input to the dom0. \todo
261: Explain why, if Xen has a serial console, the dom0 console is
262: typically also configured to open that same serial port, instead of
263: getting the passthrough input via the xen console.
264:
265: One also configures the console for the dom0. While one might expect
266: console=pc to be default, following behavior of GENERIC, a hasty read
267: of the code suggests there is no default and booting without a
268: selected console might lead to a panic. Also, there is merit in
269: explicit configuration. Therefore the standard approach is to place
270: console=pc as part of the load statement for the dom0 kernel, or
271: alternatively console=com0.
272:
273: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
274: exist), but this is not used as a console. It is used to obtain the
275: messages from the hypervisor's console; run `xl dmesg` to see them.
276:
277: ### Tuning
278:
279: In an attempt to add performance, one can also add `dom0_max_vcpus=1
280: dom0_vcpus_pin`, to force only one vcpu to be provided (since NetBSD
281: dom0 can't use more) and to pin that vcpu to a physical CPU. Xen has
282: [many boot
283: options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
284: and other than dom0 memory and max_vcpus, they are generally not
285: necessary.
286:
287: \todo Revisit this advice with current.
288: \todo Explain if anyone has ever actually measured that this helps.
289:
290: ### rc.conf
291:
292: Ensure that the boot scripts installed in
293: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
294: have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
295: but a normal part of pkgsrc usage.)
296:
297: Set `xencommons=YES` in rc.conf:
298:
299: [[!template id=filecontent name="/etc/rc.conf" text="""
300: xencommons=YES
301: """]]
302:
303: \todo Recommend for/against xen-watchdog.
304:
305: ### Testing
306:
307: Now, reboot so that you are running a DOM0 kernel under Xen, rather
308: than GENERIC without Xen.
309:
310: Once the reboot is done, use `xl` to inspect Xen's boot messages,
311: available resources, and running domains. For example:
312:
313: [[!template id=programlisting text="""
314: # xl dmesg
315: ... xen's boot info ...
316: # xl info
317: ... available memory, etc ...
318: # xl list
319: Name Id Mem(MB) CPU State Time(s) Console
320: Domain-0 0 64 0 r---- 58.1
321: """]]
322:
323: Xen logs will be in /var/log/xen.
324:
325: ### Issues with xencommons
326:
327: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
328: domUs. It does not currently work to stop and start xenstored.
329: Certainly all domUs should be shutdown first, following the sort order
330: of the rc.d scripts. However, the dom0 sets up state with xenstored,
331: and is not notified when xenstored exits, leading to not recreating
332: the state when the new xenstored starts. Until there's a mechanism to
333: make this work, one should not expect to be able to restart xenstored
334: (and thus xencommons). There is currently no reason to expect that
335: this will get fixed any time soon.
336: \todo Confirm if this is still true in 2020.
337:
338: ## Xen-specific NetBSD issues
339:
340: There are (at least) two additional things different about NetBSD as a
341: dom0 kernel compared to hardware.
342:
343: One is that through NetBSD 9 the module ABI is different because some
344: of the #defines change, so there are separate sets of modules in
345: /stand. (Further, zfs in Xen is troubled because of differing
346: MAXPHYS; see the zfs howto for more.) In NetBSD-current, there is
347: only one set of modules.
348:
349: The other difference is that XEN3_DOM0 does not have exactly the same
350: options as GENERIC. While this is roughly agreed to be in large part
351: a bug, users should be aware of this and can simply add missing config
352: items if desired.
353:
354: Finally, there have been occasional reports of trouble with X11
355: servers in NetBSD as a dom0. Some hardware support is intentionally
356: disabled in XEN3_DOM0.
357:
358: ## Updating Xen in a dom0
359:
360: Note the previous advice to maintain a working and tested boot config
361: into GENERIC without Xen.
362:
363: Updating Xen in a dom0 consists of updating the xnekernel and xentools
364: packages, along with copying the xen.gz into place, and of course
365: rebooting.
366:
367: If updating along a Xen minor version, e.g. from 4.13.1 to 4.13.2, or
368: from 4.13.2nb1 to 4.13.2nb3, it is very likely that this can be done
369: on a running system. The point is that the xentools programs will be
370: replaced, and you will be using "xl" from the new installation to talk
371: to the older programs which are still running. Problems from this
372: update path should be reported.
373:
374: For added safety, shutdown all domUs before updating, to remove the
375: need for new xl to talk to old xenstored. Note that Xen does not
376: guarantee stability of internal ABIs.
377:
378: If updating across Xen minor versions, e.g. from 4.11 to 4.13, the
379: likelihood of trouble is increased. Therefore, 'make replace' of
380: xentools on a dom0 with running domUs is not recommended. A shutdown
381: on all domUs before replacing xentools is likely sufficient. A safer
382: appraoch is to boot into GENERIC to replace the packages, as then no
383: Xen code will be running. Single user is another option.
384:
385: ## Updating NetBSD in a dom0
386:
387: This is just like updating NetBSD on bare hardware, assuming the new
388: version supports the version of Xen you are running. Generally, one
389: replaces the kernel and reboots, and then overlays userland binaries
390: and adjusts `/etc`.
391:
392: Note that one should update both the non-Xen kernel typically used for
393: rescue purposes, as well as the DOM0 kernel used with Xen.
394:
395: ## anita (for testing NetBSD)
396:
397: With a NetBSD dom0, even without any domUs, one can run anita (see
398: pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as root,
399: because anita must create a domU):
400:
401: [[!template id=programlisting text="""
402: anita --vmm=xl test file:///usr/obj/i386/
403: """]]
404:
405: # Unprivileged domains (domU)
406:
407: This section describes general concepts about domUs. It does not
408: address specific domU operating systems or how to install them. The
409: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
410: typically named so that the file name, domU name and the domU's host
411: name match.
412:
413: The domU is provided with CPU and memory by Xen, configured by the
414: dom0. The domU is provided with disk and network by the dom0,
415: mediated by Xen, and configured in the dom0.
416:
417: Entropy in domUs can be an issue; physical disks and network are on
418: the dom0. NetBSD's /dev/random system works, but is often challenged.
419:
420: ## Config files
421:
422: See /usr/pkg/share/examples/xen/xlexample* for a very small number of
423: examples for running GNU/Linux.
424:
425: The following is an example minimal domain configuration file. The
426: domU serves as a network file server.
427:
428: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
429: name = "domU-id"
430: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
431: memory = 1024
432: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
433: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
434: 'file:/n0/xen/foo-wd1,0x1,w' ]
435: """]]
436:
437: The domain will have name given in the `name` setting. The kernel has the
438: host/domU name in it, so that on the dom0 one can update the various
439: domUs independently. The `vif` line causes an interface to be provided,
440: with a specific mac address (do not reuse MAC addresses!), in bridge
441: mode. Two disks are provided, and they are both writable; the bits
442: are stored in files and Xen attaches them to a vnd(4) device in the
443: dom0 on domain creation. The system treats xbd0 as the boot device
444: without needing explicit configuration.
445:
446: There is not a type line; that implicitly defines a pv domU.
447: Otherwise, one sets type to the lower-case version of the domU type in
448: the table above; see later sections.
449:
450: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
451: that "xl create" takes the name of a config file, while other commands
452: take the name of a domain.
453:
454: Examples of commands:
455:
456: [[!template id=programlisting text="""
457: xl create /usr/pkg/etc/xen/foo
458: xl console domU-id
459: xl create -c /usr/pkg/etc/xen/foo
460: xl shutdown domU-id
461: xl list
462: """]]
463:
464: Typing `^]` will exit the console session. Shutting down a domain is
465: equivalent to pushing the power button; a NetBSD domU will receive a
466: power-press event and do a clean shutdown. Shutting down the dom0
467: will trigger controlled shutdowns of all configured domUs.
468:
469: ## CPU and memory
470:
471: A domain is provided with some number of vcpus; any domain can have up
472: to the number of CPUs seen by the hypervisor. For a domU, it is
473: controlled from the config file by the "vcpus = N" directive. It is
474: normal to overcommit vcpus; a 4-core machine machine might well provide 4
475: vcpus to each domU. One might also configure fewer vcpus for a domU.
476:
477: A domain is provided with memory; this is controlled in the config
478: file by "memory = N" (in megabytes). In the straightforward case, the
479: sum of the the memory allocated to the dom0 and all domUs must be less
480: than the available memory.
481:
482: ## Balloon driver
483:
484: Xen provides a `balloon` driver, which can be used to let domains use
485: more memory temporarily.
486:
487: \todo Explain how to set up a aystem to use the balloon scheme in a
488: useful manner.
489:
490: ## Virtual disks
491:
492: In domU config files, the disks are defined as a sequence of 3-tuples:
493:
494: * The first element is "method:/path/to/disk". Common methods are
495: "file:" for a file-backed vnd, and "phy:" for something that is already
496: a device, such as an LVM logical volume.
497:
498: * The second element is an artifact of how virtual disks are passed to
499: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
500: are given a device name to associate with the disk, and values like
501: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
502: as xbd0, the second as xbd1, and so on. However, xl demands a
503: second argument. The name given is converted to a major/minor by
504: calling stat(2) on the name in /dev and this is passed to the domU.
505: In the general case, the dom0 and domU can be different operating
506: systems, and it is an unwarranted assumption that they have consistent
507: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
508: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
509: for the second works fine and avoids this issue. For a GNU/Linux
510: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
511: /dev/hda1.
512:
513: * The third element is "w" for writable disks, and "r" for read-only
514: disks.
515:
516: Example:
517: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
518: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
519: """]]
520:
521: Note that NetBSD by default creates only vnd[0123]. If you need more
522: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
523: dom0.
524:
525: ## Virtual Networking
526:
527: Xen provides virtual Ethernets, each of which connects the dom0 and a
528: domU. For each virtual network, there is an interface "xvifN.M" in
529: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
530: The interfaces behave as if there is an Ethernet with two
531: adapters connected. From this primitive, one can construct various
532: configurations. We focus on two common and useful cases for which
533: there are existing scripts: bridging and NAT.
534:
535: With bridging (in the example above), the domU perceives itself to be
536: on the same network as the dom0. For server virtualization, this is
537: usually best. Bridging is accomplished by creating a bridge(4) device
538: and adding the dom0's physical interface and the various xvifN.0
539: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
540: config file. The bridge must be set up already in the dom0; an
541: example /etc/ifconfig.bridge0 is:
542:
543: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
544: create
545: up
546: !brconfig bridge0 add wm0
547: """]]
548:
549: With NAT, the domU perceives itself to be behind a NAT running on the
550: dom0. This is often appropriate when running Xen on a workstation.
551: TODO: NAT appears to be configured by "vif = [ '' ]".
552:
553: The MAC address specified is the one used for the interface in the new
554: domain. The interface in dom0 will use this address XOR'd with
555: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
556:
557: ## Starting domains automatically
558:
559: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
560: down cleanly on dom0 shutdown, add the following in rc.conf:
561:
562: [[!template id=filecontent name="/etc/rc.conf" text="""
563: xendomains="domU-netbsd domU-linux"
564: """]]
565:
566: # domU setup for specific systems
567:
568: Creating domUs is almost entirely independent of operating system. We
569: have already presented the basics of config files in the previous system.
570:
571: Of course, this section presumes that you have a working dom0.
572:
573: ## Creating a NetBSD PV domU
574:
575: See the earlier config file, and adjust memory. Decide on how much
576: storage you will provide, and prepare it (file or LVM).
577:
578: While the kernel will be obtained from the dom0 file system, the same
579: file should be present in the domU as /netbsd so that tools like
580: savecore(8) can work. (This is helpful but not necessary.)
581:
582: The kernel must be specifically built for Xen, to use PV interfacesas
583: a domU. NetBSD release builds provide the following kernels:
584:
585: i386 XEN3PAE_DOMU
586: amd64 XEN3_DOMU
587:
588: This will boot NetBSD, but this is not that useful if the disk is
589: empty. One approach is to unpack sets onto the disk outside of Xen
590: (by mounting it, just as you would prepare a physical disk for a
591: system you can't run the installer on).
592:
593: A second approach is to run an INSTALL kernel, which has a miniroot
594: and can load sets from the network. To do this, copy the INSTALL
595: kernel to / and change the kernel line in the config file to:
596:
597: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
598:
599: Then, start the domain as "xl create -c configfile".
600:
601: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
602: line should be used in the config file.
603:
604: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
605:
606: After booting the domain, the option to install via CDROM may be
607: selected. The CDROM device should be changed to `xbd1d`.
608:
609: Once done installing, "halt -p" the new domain (don't reboot or halt:
610: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
611: config file), switch the config file back to the XEN3_DOMU kernel,
612: and start the new domain again. Now it should be able to use "root on
613: xbd0a" and you should have a functional NetBSD domU.
614:
615: TODO: check if this is still accurate.
616: When the new domain is booting you'll see some warnings about *wscons*
617: and the pseudo-terminals. These can be fixed by editing the files
618: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
619: `/etc/ttys`, except *console*, like this:
620:
621: console "/usr/libexec/getty Pc" vt100 on secure
622: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
623: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
624: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
625: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
626:
627: Finally, all screens must be commented out from `/etc/wscons.conf`.
628:
629: One should also run `powerd` in a domU, but this should not need
630: configuring. With powerd, the domain will run a controlled shutdown
631: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
632: receiving a synthetic `power button pressed` signal. In 9 and
633: current, `powerd` is run by default under Xen kernels (or if ACPI is
634: present), and it can be added to rc.conf if not.
635:
636: It is not strictly necessary to have a kernel (as /netbsd) in the domU
637: file system. However, various programs (e.g. netstat) will use that
638: kernel to look up symbols to read from kernel virtual memory. If
639: /netbsd is not the running kernel, those lookups will fail. (This is
640: not really a Xen-specific issue, but because the domU kernel is
641: obtained from the dom0, it is far more likely to be out of sync or
642: missing with Xen.)
643:
644: Note that NetBSD by default creates only xbd[0123]. If you need more
645: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
646:
647: ## Creating a Linux PV domU
648:
649: Creating unprivileged Linux domains isn't much different from
650: unprivileged NetBSD domains, but there are some details to know.
651:
652: First, the second parameter passed to the disk declaration (the '0x1' in
653: the example below)
654:
655: disk = [ 'phy:/dev/wd0e,0x1,w' ]
656:
657: does matter to Linux. It wants a Linux device number here (e.g. 0x300
658: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
659: So, hda1 which has major 3 and minor 1 on a Linux system will have
660: device number 0x301. Alternatively, devices names can be used (hda,
661: hdb, ...) as xentools has a table to map these names to devices
662: numbers. To export a partition to a Linux guest we can use:
663:
664: disk = [ 'phy:/dev/wd0e,0x300,w' ]
665: root = "/dev/hda1 ro"
666:
667: and it will appear as /dev/hda on the Linux system, and be used as root
668: partition.
669:
670: To install the Linux system on the partition to be exported to the
671: guest domain, the following method can be used: install
672: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
673: that will be the root partition of your Linux domain, and mount it.
674: Then copy the files from a working Linux system, make adjustments in
675: `/etc` (fstab, network config). It should also be possible to extract
676: binary packages such as .rpm or .deb directly to the mounted partition
677: using the appropriate tool, possibly running under NetBSD's Linux
678: emulation. Once the file system has been populated, umount it. If
679: desirable, the file system can be converted to ext3 using tune2fs -j.
680: It should now be possible to boot the Linux guest domain, using one of
681: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
682:
683: To get the Linux console right, you need to add:
684:
685: extra = "xencons=tty1"
686:
687: to your configuration since not all Linux distributions auto-attach a
688: tty to the xen console.
689:
690: ## Creating a NetBSD HVM domU
691:
692: Use type='hvm', probably. Use a GENERIC kernel within the disk image.
693:
694: ## Creating a NetBSD PVH domU
695:
696: This only works with a current kernel in the domU.
697:
698: Use type='pvh'. Probably, use a GENERIC kernel within the disk image,
699: which in current has PV support.
700:
701: \todo Verify.
702:
703: \todo Verify if one can have current PVH domU on a 9 dom0.
704:
705: ## Creating a Solaris domU
706:
707: See possibly outdated
708: [Solaris domU instructions](/ports/xen/howto-solaris/).
709:
710: ## PCI passthrough: Using PCI devices in guest domains
711:
712: NB: PCI passthrough only works on some Xen versions and as of 2020 it
713: is not clear that it works on any version in pkgsrc. \todo Reports
714: confirming or denying this notion should be sent to port-xen@.
715:
716: The dom0 can give other domains access to selected PCI
717: devices. This can allow, for example, a non-privileged domain to have
718: access to a physical network interface or disk controller. However,
719: keep in mind that giving a domain access to a PCI device most likely
720: will give the domain read/write access to the whole physical memory,
721: as PCs don't have an IOMMU to restrict memory access to DMA-capable
722: device. Also, it's not possible to export ISA devices to non-dom0
723: domains, which means that the primary VGA adapter can't be exported.
724: A guest domain trying to access the VGA registers will panic.
725:
726: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
727: not been ported to later versions at this time.
728:
729: For a PCI device to be exported to a domU, is has to be attached to
730: the "pciback" driver in dom0. Devices passed to the dom0 via the
731: pciback.hide boot parameter will attach to "pciback" instead of the
732: usual driver. The list of devices is specified as "(bus:dev.func)",
733: where bus and dev are 2-digit hexadecimal numbers, and func a
734: single-digit number:
735:
736: pciback.hide=(00:0a.0)(00:06.0)
737:
738: pciback devices should show up in the dom0's boot messages, and the
739: devices should be listed in the `/kern/xen/pci` directory.
740:
741: PCI devices to be exported to a domU are listed in the "pci" array of
742: the domU's config file, with the format "0000:bus:dev.func".
743:
744: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
745:
746: In the domU an "xpci" device will show up, to which one or more pci
747: buses will attach. Then the PCI drivers will attach to PCI buses as
748: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
749: or any PCI drivers built in by default; you have to build your own
750: kernel to use PCI devices in a domU. Here's a kernel config example;
751: note that only the "xpci" lines are unusual.
752:
753: include "arch/i386/conf/XEN3_DOMU"
754:
755: # Add support for PCI buses to the XEN3_DOMU kernel
756: xpci* at xenbus ?
757: pci* at xpci ?
758:
759: # PCI USB controllers
760: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
761:
762: # USB bus support
763: usb* at uhci?
764:
765: # USB Hubs
766: uhub* at usb?
767: uhub* at uhub? port ? configuration ? interface ?
768:
769: # USB Mass Storage
770: umass* at uhub? port ? configuration ? interface ?
771: wd* at umass?
772: # SCSI controllers
773: ahc* at pci? dev ? function ? # Adaptec [23]94x, aic78x0 SCSI
774:
775: # SCSI bus support (for both ahc and umass)
776: scsibus* at scsi?
777:
778: # SCSI devices
779: sd* at scsibus? target ? lun ? # SCSI disk drives
780: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
781:
782:
783: # Miscellaneous Information
784:
785: ## Nesting under Linux KVM
786:
787: It is possible to run Xen and a NetBSD dom0 under Linux KVM. One
788: can enable virtio in the dom0 for greater speed.
789:
790: ## Nesting under qemu
791:
792: It is possible to run Xen and a NetBSD dom0 under qemu on NetBSD, and
793: also with nvmm.
794: \todo Check this.
795:
796: ## Other nesting
797:
798: In theory, any full emulation should be able to run Xen and a NetBSD
799: dom0. The HOWTO does not currently have information about Xen XVM
800: mode, Virtualbox, etc.
801:
802: ## NetBSD 5 as domU
803:
804: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
805: (However, NetBSD 5 systems should be updated to a supported version.)
806:
807: # NetBSD as a domU in a VPS
808:
809: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
810: hardware. This section explains how to deal with Xen in a domU as a
811: virtual private server where you do not control or have access to the
812: dom0. This is not intended to be an exhaustive list of VPS providers;
813: only a few are mentioned that specifically support NetBSD.
814:
815: VPS operators provide varying degrees of access and mechanisms for
816: configuration. The big issue is usually how one controls which kernel
817: is booted, because the kernel is nominally in the dom0 file system (to
818: which VPS users do not normally have access). A second issue is how
819: to install NetBSD.
820: A VPS user may want to compile a kernel for security updates, to run
821: npf, run IPsec, or any other reason why someone would want to change
822: their kernel.
823:
824: One approach is to have an administrative interface to upload a kernel,
825: or to select from a prepopulated list. Other approaches are pygrub
826: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
827: kernel from the domU file system. This is closer to a regular physical
828: computer, where someone who controls a machine can replace the kernel.
829:
830: A second issue is multiple CPUs. With NetBSD 6, domUs support
831: multiple vcpus, and it is typical for VPS providers to enable multiple
832: CPUs for NetBSD domUs.
833:
834: ## Complexities due to Xen changes
835:
836: Xen has many security advisories and people running Xen systems make
837: different choices.
838:
839: ### stub domains
840:
841: Some (Linux) dom0 systems use something called "stub domains" to
842: isolate qemu from the dom0 system, as a security and reliabilty
843: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
844: ends up using PIO for disks rather than DMA. Of course, all of this
845: is emulated, but emulated PIO is unusably slow. This problem is not
846: currently understood.
847:
848: ### Grant tables
849:
850: There are multiple versions of using grant tables, and some security
851: advisories have suggested disabling some versions. NetBSD through 9
852: uses version 1 and NetBSD-current uses version 2. This can lead to
853: "NetBSD current doesn't run on hosting provider X" situations.
854:
855: \todo Explain better.
856:
857: ## Boot methods
858:
859: ### pvgrub
860:
861: pvgrub is a version of grub that uses PV operations instead of BIOS
862: calls. It is booted from the dom0 as the domU kernel, and then reads
863: /grub/menu.lst and loads a kernel from the domU file system.
864:
865: It appears that [grub's FFS
866: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
867: does not support all aspects of modern FFS, but there are also reports
868: that FFSv2 works fine.
869:
870: ### pygrub
871:
872: As of 2014, pygrub seems to be of mostly historical interest. As of
873: 2021, the section should perhaps be outright deleted.
874:
875: pygrub runs in the dom0 and looks into the domU file system. This
876: implies that the domU must have a kernel in a file system in a format
877: known to pygrub.
878:
879: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
880: and is inherently less secure than pvgrub due to running inside
881: dom0. For both these reasons, pygrub should not be used, and is only
882: still present so that historical DomU images using it still work.
883:
884: ## Specific Providers
885:
886: The intent is to list providers only if they document support for
887: running NetBSD, and to point to their resources briefly.
888:
889: ### panix.com
890:
891: [Panix](http://www.panix.com/) provides NetBSD as an OS option. See
892: https://www.panix.com/v-colo/nupgrade.html for some information.
893: Users can use pvgrub. Panix reports that pvgrub works with FFsv2 with
894: 16K/2K and 32K/4K block/frag sizes (and hence with defaults from
895: "newfs -O 2"). See [Panix's pvgrub
896: page](http://www.panix.com/v-colo/grub.html) which describes how to
897: boot NetBSD.
898:
899: ### prgmr.com
900:
901: [prgmr.com](http://prgmr.com/) provides released versions of
902: NetBSD/amd64 as installation options. Users can use pvgrub to boot
903: their own kernel, and a small FAT32 /boot is encouraged. See the
904: [prgmr.com NetBSD
905: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
906: (which is in need of updating).
907:
908: ### Amazon
909:
910: See the [Amazon EC2 page](/amazon_ec2/).
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