1: [[!meta title="Xen Status and 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 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).
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
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
26: # Overview
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.
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.
38: There are many choices one can make; the HOWTO recommends the standard
39: approach and limits discussion of alternatives in many cases.
41: ## Guest Styles
43: Xen supports different styles of guests. See
44: https://wiki.xenproject.org/wiki/Virtualization_Spectrum for a
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.
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
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
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.
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).
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
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.)
88: ## CPU Architecture
90: Xen runs on x86_64 hardware (the NetBSD amd64 port).
92: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
94: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
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.
100: ## Xen Versions
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.
107: Versions available in pkgsrc:
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
115: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
117: Older Xen had a python-based management tool called xm; this has been
118: replaced by xl.
120: ## NetBSD versions
122: Xen has been supported in NetBSD for a long time, at least since 2005.
123: Initially Xen was PV only.
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
129: Support for PVHVM and PVH is available only in NetBSD-current; this is
130: currently somewhat experimental, although PVHVM appears reasonably
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.
138: NetBSD-current supports SMP in dom0, and XEN3_DOM0 includes "options
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".
145: Note that while Xen 4.13 is current, the kernel support is still
146: called XEN3, because the hypercall interface has not changed
149: # Creating a NetBSD dom0
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.
155: NB: As of 2021-04, you must arrange to have the system use BIOS boot,
156: not EFI boot. (Perhaps, with recent current and using multiboot
157: instead of NetBSD boot, this might not be true.)
159: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
160: 512M it worked reliably. This does not make sense, but if you see
161: "not ELF" after Xen boots, try increasing dom0 RAM.
163: ## Installation of NetBSD
165: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
166: using Xen. Therefore, use the most recent release, or a build from
167: the most recent stable branch. Alternatively, use -current, being
168: mindful of all the usual caveats of lower stability of current, and
169: likely a bit more so. Think about how you will provide storage for
170: disk images.
172: ## Installation of Xen
174: ### Building Xen
176: Use the most recent version of Xen in pkgsrc, unless the DESCR says
177: that it is not suitable. Therefore, choose 4.13. In the dom0,
178: install xenkernel413 and xentools413 from pkgsrc.
180: Once this is done, copy the Xen kernel from where pkgsrc puts it to
181: where the boot process will be able to find it:
183: [[!template id=programlisting text="""
184: # cp -p /usr/pkg/xen413-kernel/xen.gz /
187: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
188: kernel can either be taken from a local release build.sh run, compiled
189: manually, or downloaded from the NetBSD FTP, for example at:
191: [[!template id=programlisting text="""
195: ### Configuring booting
197: Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen,
198: adjusting for your root filesystem:
200: [[!template id=filecontent name="/boot.cfg" text="""
201: menu=Xen:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc;multiboot /xen.gz dom0_mem=512M
202: menu=Xen single user:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc -s;multiboot /xen.gz dom0_mem=512M
205: This specifies that the dom0 should have 512MB of ram, leaving the rest
206: to be allocated for domUs.
208: NB: This says add, not replace, so that you will be able to more
209: easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may
210: want to set it as default. It is highly likely that you will have
211: trouble at some point, and keeping an up-to-date GENERIC for use in
212: fixing problems is the standard prudent approach.
214: \todo Explain why rndseed is not set with Xen as part of the dom0
217: Note that you are likely to have to set root= because the boot device
218: from /boot is not passed via Xen to the dom0 kernel. With one disk,
219: it will work, but e.g. plugging in USB disk to a machine with root on
220: wd0a causes boot to fail.
222: Beware that userconf statements must be attached to the dom0 load, and
223: may not be at top-level, because then they would try to configure the
224: hypervisor, if there is a way to pass them via multiboot. It appears
225: that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very
226: early with a heap overflow.
228: ### Console selection
230: See boot_console(8). Understand that you should start from a place of
231: having console setup correct for booting GENERIC before trying to
232: configure Xen.
234: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
235: equivalent, and this is passed on to /boot (where one typically does
236: not set the console). This configuration of bootxx_ffsv1 should also
237: be in place for Xen systems, to allow seeing messages from /boot and
238: use of a keyboard to select a line from the menu. And, one should
239: have a working boot path to GENERIC for rescue situations.
241: With GENERIC, the boot options are passed on to /netbsd, but there is
242: currently no mechanism to pass these via multiboot to the hypervisor.
243: Thus, in addition to configuring the console in the boot blocks, one
244: must also configure it for Xen.
246: By default, the hypervisor (Xen itself) will use some sort of vga
247: device as the console, much like GENERIC uses by default. The vga
248: console is relinquished at the conclusion of hypervisor boot, before
249: the dom0 is started. Xen when using a vga console does not process
250: console input.
252: The hypervisor can be configured to use a serial port console, e.g.
253: [[!template id=filecontent name="/boot.cfg" text="""
254: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
256: This example uses the first serial port (Xen counts from 1; this is
257: what NetBSD would call com0), and sets speed and parity. (The dom0 is
258: then configured to use the same serial port in this example.)
260: With the hypervisor configured for a serial console, it can get input,
261: and there is a notion of passing this input to the dom0. \todo
262: Explain why, if Xen has a serial console, the dom0 console is
263: typically also configured to open that same serial port, instead of
264: getting the passthrough input via the xen console.
266: One also configures the console for the dom0. While one might expect
267: console=pc to be default, following behavior of GENERIC, a hasty read
268: of the code suggests there is no default and booting without a
269: selected console might lead to a panic. Also, there is merit in
270: explicit configuration. Therefore the standard approach is to place
271: console=pc as part of the load statement for the dom0 kernel, or
272: alternatively console=com0.
274: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
275: exist), but this is not used as a console. It is used to obtain the
276: messages from the hypervisor's console; run `xl dmesg` to see them.
278: ### Tuning
280: In an attempt to add performance, one can also add `dom0_max_vcpus=1
281: dom0_vcpus_pin`, to force only one vcpu to be provided (since NetBSD
282: dom0 can't use more) and to pin that vcpu to a physical CPU. Xen has
283: [many boot
285: and other than dom0 memory and max_vcpus, they are generally not
288: \todo Revisit this advice with current.
289: \todo Explain if anyone has ever actually measured that this helps.
291: ### rc.conf
293: Ensure that the boot scripts installed in
294: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
295: have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
296: but a normal part of pkgsrc usage.)
298: Set `xencommons=YES` in rc.conf:
300: [[!template id=filecontent name="/etc/rc.conf" text="""
304: \todo Recommend for/against xen-watchdog.
306: ### Testing
308: Now, reboot so that you are running a DOM0 kernel under Xen, rather
309: than GENERIC without Xen.
311: Once the reboot is done, use `xl` to inspect Xen's boot messages,
312: available resources, and running domains. For example:
314: [[!template id=programlisting text="""
315: # xl dmesg
316: ... xen's boot info ...
317: # xl info
318: ... available memory, etc ...
319: # xl list
320: Name Id Mem(MB) CPU State Time(s) Console
321: Domain-0 0 64 0 r---- 58.1
324: Xen logs will be in /var/log/xen.
326: ### Issues with xencommons
328: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
329: domUs. It does not currently work to stop and start xenstored.
330: Certainly all domUs should be shutdown first, following the sort order
331: of the rc.d scripts. However, the dom0 sets up state with xenstored,
332: and is not notified when xenstored exits, leading to not recreating
333: the state when the new xenstored starts. Until there's a mechanism to
334: make this work, one should not expect to be able to restart xenstored
335: (and thus xencommons). There is currently no reason to expect that
336: this will get fixed any time soon.
337: \todo Confirm if this is still true in 2020.
339: ## Xen-specific NetBSD issues
341: There are (at least) two additional things different about NetBSD as a
342: dom0 kernel compared to hardware.
344: One is that through NetBSD 9 the module ABI is different because some
345: of the #defines change, so there are separate sets of modules in
346: /stand. (Further, zfs in Xen is troubled because of differing
347: MAXPHYS; see the zfs howto for more.) In NetBSD-current, there is
348: only one set of modules.
350: The other difference is that XEN3_DOM0 does not have exactly the same
351: options as GENERIC. While this is roughly agreed to be in large part
352: a bug, users should be aware of this and can simply add missing config
353: items if desired.
355: Finally, there have been occasional reports of trouble with X11
356: servers in NetBSD as a dom0. Some hardware support is intentionally
357: disabled in XEN3_DOM0.
359: ## Updating Xen in a dom0
361: Note the previous advice to maintain a working and tested boot config
362: into GENERIC without Xen.
364: Updating Xen in a dom0 consists of updating the xnekernel and xentools
365: packages, along with copying the xen.gz into place, and of course
368: If updating along a Xen minor version, e.g. from 4.13.1 to 4.13.2, or
369: from 4.13.2nb1 to 4.13.2nb3, it is very likely that this can be done
370: on a running system. The point is that the xentools programs will be
371: replaced, and you will be using "xl" from the new installation to talk
372: to the older programs which are still running. Problems from this
373: update path should be reported.
375: For added safety, shutdown all domUs before updating, to remove the
376: need for new xl to talk to old xenstored. Note that Xen does not
377: guarantee stability of internal ABIs.
379: If updating across Xen minor versions, e.g. from 4.11 to 4.13, the
380: likelihood of trouble is increased. Therefore, 'make replace' of
381: xentools on a dom0 with running domUs is not recommended. A shutdown
382: on all domUs before replacing xentools is likely sufficient. A safer
383: appraoch is to boot into GENERIC to replace the packages, as then no
384: Xen code will be running. Single user is another option.
386: ## Updating NetBSD in a dom0
388: This is just like updating NetBSD on bare hardware, assuming the new
389: version supports the version of Xen you are running. Generally, one
390: replaces the kernel and reboots, and then overlays userland binaries
391: and adjusts `/etc`.
393: Note that one should update both the non-Xen kernel typically used for
394: rescue purposes, as well as the DOM0 kernel used with Xen.
396: ## anita (for testing NetBSD)
398: With a NetBSD dom0, even without any domUs, one can run anita (see
399: pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as root,
400: because anita must create a domU):
402: [[!template id=programlisting text="""
403: anita --vmm=xl test file:///usr/obj/i386/
406: # Unprivileged domains (domU)
408: This section describes general concepts about domUs. It does not
409: address specific domU operating systems or how to install them. The
410: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
411: typically named so that the file name, domU name and the domU's host
412: name match.
414: The domU is provided with CPU and memory by Xen, configured by the
415: dom0. The domU is provided with disk and network by the dom0,
416: mediated by Xen, and configured in the dom0.
418: Entropy in domUs can be an issue; physical disks and network are on
419: the dom0. NetBSD's /dev/random system works, but is often challenged.
421: ## Config files
423: See /usr/pkg/share/examples/xen/xlexample* for a very small number of
424: examples for running GNU/Linux.
426: The following is an example minimal domain configuration file. The
427: domU serves as a network file server.
429: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
430: name = "domU-id"
431: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
432: memory = 1024
433: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
434: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
435: 'file:/n0/xen/foo-wd1,0x1,w' ]
438: The domain will have name given in the `name` setting. The kernel has the
439: host/domU name in it, so that on the dom0 one can update the various
440: domUs independently. The `vif` line causes an interface to be provided,
441: with a specific mac address (do not reuse MAC addresses!), in bridge
442: mode. Two disks are provided, and they are both writable; the bits
443: are stored in files and Xen attaches them to a vnd(4) device in the
444: dom0 on domain creation. The system treats xbd0 as the boot device
445: without needing explicit configuration.
447: There is not a type line; that implicitly defines a pv domU.
448: Otherwise, one sets type to the lower-case version of the domU type in
449: the table above; see later sections.
451: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
452: that "xl create" takes the name of a config file, while other commands
453: take the name of a domain.
455: Examples of commands:
457: [[!template id=programlisting text="""
458: xl create /usr/pkg/etc/xen/foo
459: xl console domU-id
460: xl create -c /usr/pkg/etc/xen/foo
461: xl shutdown domU-id
462: xl list
465: Typing `^]` will exit the console session. Shutting down a domain is
466: equivalent to pushing the power button; a NetBSD domU will receive a
467: power-press event and do a clean shutdown. Shutting down the dom0
468: will trigger controlled shutdowns of all configured domUs.
470: ## CPU and memory
472: A domain is provided with some number of vcpus; any domain can have up
473: to the number of CPUs seen by the hypervisor. For a domU, it is
474: controlled from the config file by the "vcpus = N" directive. It is
475: normal to overcommit vcpus; a 4-core machine machine might well provide 4
476: vcpus to each domU. One might also configure fewer vcpus for a domU.
478: A domain is provided with memory; this is controlled in the config
479: file by "memory = N" (in megabytes). In the straightforward case, the
480: sum of the the memory allocated to the dom0 and all domUs must be less
481: than the available memory.
483: ## Balloon driver
485: Xen provides a `balloon` driver, which can be used to let domains use
486: more memory temporarily.
488: \todo Explain how to set up a aystem to use the balloon scheme in a
489: useful manner.
491: ## Virtual disks
493: In domU config files, the disks are defined as a sequence of 3-tuples:
495: * The first element is "method:/path/to/disk". Common methods are
496: "file:" for a file-backed vnd, and "phy:" for something that is already
497: a device, such as an LVM logical volume.
499: * The second element is an artifact of how virtual disks are passed to
500: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
501: are given a device name to associate with the disk, and values like
502: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
503: as xbd0, the second as xbd1, and so on. However, xl demands a
504: second argument. The name given is converted to a major/minor by
505: calling stat(2) on the name in /dev and this is passed to the domU.
506: In the general case, the dom0 and domU can be different operating
507: systems, and it is an unwarranted assumption that they have consistent
508: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
509: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
510: for the second works fine and avoids this issue. For a GNU/Linux
511: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
514: * The third element is "w" for writable disks, and "r" for read-only
518: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
519: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
522: Note that NetBSD by default creates only vnd. If you need more
523: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
526: ## Virtual Networking
528: Xen provides virtual Ethernets, each of which connects the dom0 and a
529: domU. For each virtual network, there is an interface "xvifN.M" in
530: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
531: The interfaces behave as if there is an Ethernet with two
532: adapters connected. From this primitive, one can construct various
533: configurations. We focus on two common and useful cases for which
534: there are existing scripts: bridging and NAT.
536: With bridging (in the example above), the domU perceives itself to be
537: on the same network as the dom0. For server virtualization, this is
538: usually best. Bridging is accomplished by creating a bridge(4) device
539: and adding the dom0's physical interface and the various xvifN.0
540: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
541: config file. The bridge must be set up already in the dom0; an
542: example /etc/ifconfig.bridge0 is:
544: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
547: !brconfig bridge0 add wm0
550: With NAT, the domU perceives itself to be behind a NAT running on the
551: dom0. This is often appropriate when running Xen on a workstation.
552: TODO: NAT appears to be configured by "vif = [ '' ]".
554: The MAC address specified is the one used for the interface in the new
555: domain. The interface in dom0 will use this address XOR'd with
556: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
558: ## Starting domains automatically
560: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
561: down cleanly on dom0 shutdown, add the following in rc.conf:
563: [[!template id=filecontent name="/etc/rc.conf" text="""
564: xendomains="domU-netbsd domU-linux"
567: # domU setup for specific systems
569: Creating domUs is almost entirely independent of operating system. We
570: have already presented the basics of config files in the previous system.
572: Of course, this section presumes that you have a working dom0.
574: ## Creating a NetBSD PV domU
576: See the earlier config file, and adjust memory. Decide on how much
577: storage you will provide, and prepare it (file or LVM).
579: While the kernel will be obtained from the dom0 file system, the same
580: file should be present in the domU as /netbsd so that tools like
581: savecore(8) can work. (This is helpful but not necessary.)
583: The kernel must be specifically built for Xen, to use PV interfacesas
584: a domU. NetBSD release builds provide the following kernels:
586: i386 XEN3PAE_DOMU
587: amd64 XEN3_DOMU
589: This will boot NetBSD, but this is not that useful if the disk is
590: empty. One approach is to unpack sets onto the disk outside of Xen
591: (by mounting it, just as you would prepare a physical disk for a
592: system you can't run the installer on).
594: A second approach is to run an INSTALL kernel, which has a miniroot
595: and can load sets from the network. To do this, copy the INSTALL
596: kernel to / and change the kernel line in the config file to:
598: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
600: Then, start the domain as "xl create -c configfile".
602: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
603: line should be used in the config file.
605: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
607: After booting the domain, the option to install via CDROM may be
608: selected. The CDROM device should be changed to `xbd1d`.
610: Once done installing, "halt -p" the new domain (don't reboot or halt:
611: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
612: config file), switch the config file back to the XEN3_DOMU kernel,
613: and start the new domain again. Now it should be able to use "root on
614: xbd0a" and you should have a functional NetBSD domU.
616: TODO: check if this is still accurate.
617: When the new domain is booting you'll see some warnings about *wscons*
618: and the pseudo-terminals. These can be fixed by editing the files
619: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
620: `/etc/ttys`, except *console*, like this:
622: console "/usr/libexec/getty Pc" vt100 on secure
623: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
624: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
625: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
626: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
628: Finally, all screens must be commented out from `/etc/wscons.conf`.
630: One should also run `powerd` in a domU, but this should not need
631: configuring. With powerd, the domain will run a controlled shutdown
632: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
633: receiving a synthetic `power button pressed` signal. In 9 and
634: current, `powerd` is run by default under Xen kernels (or if ACPI is
635: present), and it can be added to rc.conf if not.
637: It is not strictly necessary to have a kernel (as /netbsd) in the domU
638: file system. However, various programs (e.g. netstat) will use that
639: kernel to look up symbols to read from kernel virtual memory. If
640: /netbsd is not the running kernel, those lookups will fail. (This is
641: not really a Xen-specific issue, but because the domU kernel is
642: obtained from the dom0, it is far more likely to be out of sync or
643: missing with Xen.)
645: Note that NetBSD by default creates only xbd. If you need more
646: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
648: ## Creating a Linux PV domU
650: Creating unprivileged Linux domains isn't much different from
651: unprivileged NetBSD domains, but there are some details to know.
653: First, the second parameter passed to the disk declaration (the '0x1' in
654: the example below)
656: disk = [ 'phy:/dev/wd0e,0x1,w' ]
658: does matter to Linux. It wants a Linux device number here (e.g. 0x300
659: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
660: So, hda1 which has major 3 and minor 1 on a Linux system will have
661: device number 0x301. Alternatively, devices names can be used (hda,
662: hdb, ...) as xentools has a table to map these names to devices
663: numbers. To export a partition to a Linux guest we can use:
665: disk = [ 'phy:/dev/wd0e,0x300,w' ]
666: root = "/dev/hda1 ro"
668: and it will appear as /dev/hda on the Linux system, and be used as root
671: To install the Linux system on the partition to be exported to the
672: guest domain, the following method can be used: install
673: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
674: that will be the root partition of your Linux domain, and mount it.
675: Then copy the files from a working Linux system, make adjustments in
676: `/etc` (fstab, network config). It should also be possible to extract
677: binary packages such as .rpm or .deb directly to the mounted partition
678: using the appropriate tool, possibly running under NetBSD's Linux
679: emulation. Once the file system has been populated, umount it. If
680: desirable, the file system can be converted to ext3 using tune2fs -j.
681: It should now be possible to boot the Linux guest domain, using one of
682: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
684: To get the Linux console right, you need to add:
686: extra = "xencons=tty1"
688: to your configuration since not all Linux distributions auto-attach a
689: tty to the xen console.
691: ## Creating a NetBSD HVM domU
693: Use type='hvm', probably. Use a GENERIC kernel within the disk image.
695: ## Creating a NetBSD PVH domU
697: This only works with a current kernel in the domU.
699: Use type='pvh'. Probably, use a GENERIC kernel within the disk image,
700: which in current has PV support.
702: \todo Verify.
704: \todo Verify if one can have current PVH domU on a 9 dom0.
706: ## Creating a Solaris domU
708: See possibly outdated
709: [Solaris domU instructions](/ports/xen/howto-solaris/).
711: ## PCI passthrough: Using PCI devices in guest domains
713: NB: PCI passthrough only works on some Xen versions and as of 2020 it
714: is not clear that it works on any version in pkgsrc. \todo Reports
715: confirming or denying this notion should be sent to port-xen@.
717: The dom0 can give other domains access to selected PCI
718: devices. This can allow, for example, a non-privileged domain to have
719: access to a physical network interface or disk controller. However,
720: keep in mind that giving a domain access to a PCI device most likely
721: will give the domain read/write access to the whole physical memory,
722: as PCs don't have an IOMMU to restrict memory access to DMA-capable
723: device. Also, it's not possible to export ISA devices to non-dom0
724: domains, which means that the primary VGA adapter can't be exported.
725: A guest domain trying to access the VGA registers will panic.
727: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
728: not been ported to later versions at this time.
730: For a PCI device to be exported to a domU, is has to be attached to
731: the "pciback" driver in dom0. Devices passed to the dom0 via the
732: pciback.hide boot parameter will attach to "pciback" instead of the
733: usual driver. The list of devices is specified as "(bus:dev.func)",
734: where bus and dev are 2-digit hexadecimal numbers, and func a
735: single-digit number:
739: pciback devices should show up in the dom0's boot messages, and the
740: devices should be listed in the `/kern/xen/pci` directory.
742: PCI devices to be exported to a domU are listed in the "pci" array of
743: the domU's config file, with the format "0000:bus:dev.func".
745: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
747: In the domU an "xpci" device will show up, to which one or more pci
748: buses will attach. Then the PCI drivers will attach to PCI buses as
749: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
750: or any PCI drivers built in by default; you have to build your own
751: kernel to use PCI devices in a domU. Here's a kernel config example;
752: note that only the "xpci" lines are unusual.
754: include "arch/i386/conf/XEN3_DOMU"
756: # Add support for PCI buses to the XEN3_DOMU kernel
757: xpci* at xenbus ?
758: pci* at xpci ?
760: # PCI USB controllers
761: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
763: # USB bus support
764: usb* at uhci?
766: # USB Hubs
767: uhub* at usb?
768: uhub* at uhub? port ? configuration ? interface ?
770: # USB Mass Storage
771: umass* at uhub? port ? configuration ? interface ?
772: wd* at umass?
773: # SCSI controllers
774: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
776: # SCSI bus support (for both ahc and umass)
777: scsibus* at scsi?
779: # SCSI devices
780: sd* at scsibus? target ? lun ? # SCSI disk drives
781: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
784: # Miscellaneous Information
786: ## Nesting under Linux KVM
788: It is possible to run Xen and a NetBSD dom0 under Linux KVM. One
789: can enable virtio in the dom0 for greater speed.
791: ## Nesting under qemu
793: It is possible to run Xen and a NetBSD dom0 under qemu on NetBSD, and
794: also with nvmm.
795: \todo Check this.
797: ## Other nesting
799: In theory, any full emulation should be able to run Xen and a NetBSD
800: dom0. The HOWTO does not currently have information about Xen XVM
801: mode, Virtualbox, etc.
803: ## NetBSD 5 as domU
805: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
806: (However, NetBSD 5 systems should be updated to a supported version.)
808: # NetBSD as a domU in a VPS
810: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
811: hardware. This section explains how to deal with Xen in a domU as a
812: virtual private server where you do not control or have access to the
813: dom0. This is not intended to be an exhaustive list of VPS providers;
814: only a few are mentioned that specifically support NetBSD.
816: VPS operators provide varying degrees of access and mechanisms for
817: configuration. The big issue is usually how one controls which kernel
818: is booted, because the kernel is nominally in the dom0 file system (to
819: which VPS users do not normally have access). A second issue is how
820: to install NetBSD.
821: A VPS user may want to compile a kernel for security updates, to run
822: npf, run IPsec, or any other reason why someone would want to change
823: their kernel.
825: One approach is to have an administrative interface to upload a kernel,
826: or to select from a prepopulated list. Other approaches are pygrub
827: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
828: kernel from the domU file system. This is closer to a regular physical
829: computer, where someone who controls a machine can replace the kernel.
831: A second issue is multiple CPUs. With NetBSD 6, domUs support
832: multiple vcpus, and it is typical for VPS providers to enable multiple
833: CPUs for NetBSD domUs.
835: ## Complexities due to Xen changes
837: Xen has many security advisories and people running Xen systems make
838: different choices.
840: ### stub domains
842: Some (Linux) dom0 systems use something called "stub domains" to
843: isolate qemu from the dom0 system, as a security and reliabilty
844: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
845: ends up using PIO for disks rather than DMA. Of course, all of this
846: is emulated, but emulated PIO is unusably slow. This problem is not
847: currently understood.
849: ### Grant tables
851: There are multiple versions of using grant tables, and some security
852: advisories have suggested disabling some versions. NetBSD through 9
853: uses version 1 and NetBSD-current uses version 2. This can lead to
854: "NetBSD current doesn't run on hosting provider X" situations.
856: \todo Explain better.
858: ## Boot methods
860: ### pvgrub
862: pvgrub is a version of grub that uses PV operations instead of BIOS
863: calls. It is booted from the dom0 as the domU kernel, and then reads
864: /grub/menu.lst and loads a kernel from the domU file system.
866: It appears that [grub's FFS
868: does not support all aspects of modern FFS, but there are also reports
869: that FFSv2 works fine.
871: ### pygrub
873: As of 2014, pygrub seems to be of mostly historical interest. As of
874: 2021, the section should perhaps be outright deleted.
876: pygrub runs in the dom0 and looks into the domU file system. This
877: implies that the domU must have a kernel in a file system in a format
878: known to pygrub.
880: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
881: and is inherently less secure than pvgrub due to running inside
882: dom0. For both these reasons, pygrub should not be used, and is only
883: still present so that historical DomU images using it still work.
885: ## Specific Providers
887: The intent is to list providers only if they document support for
888: running NetBSD, and to point to their resources briefly.
890: ### panix.com
892: [Panix](http://www.panix.com/) provides NetBSD as an OS option. See
893: https://www.panix.com/v-colo/nupgrade.html for some information.
894: Users can use pvgrub. Panix reports that pvgrub works with FFsv2 with
895: 16K/2K and 32K/4K block/frag sizes (and hence with defaults from
896: "newfs -O 2"). See [Panix's pvgrub
897: page](http://www.panix.com/v-colo/grub.html) which describes how to
898: boot NetBSD.
900: ### prgmr.com
902: [prgmr.com](http://prgmr.com/) provides released versions of
903: NetBSD/amd64 as installation options. Users can use pvgrub to boot
904: their own kernel, and a small FAT32 /boot is encouraged. See the
905: [prgmr.com NetBSD
907: (which is in need of updating).
909: ### Amazon
911: See the [Amazon EC2 page](/amazon_ec2/).
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