1: [[!meta title="Xen 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 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
14: website](http://www.xenproject.org/).
15:
16: [[!toc]]
17:
18: # Overview
19:
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.
24:
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.
29:
30: There are many choices one can make; the HOWTO recommends the standard
31: approach and limits discussion of alternatives in many cases.
32:
33: ## Guest Styles
34:
35: Xen supports different styles of guests.
36:
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)
43: """]]
44:
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\)).
49:
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. It is therefore non-sensical
53: to have an HVM dom0.
54:
55: In PVHVM mode, the guest runs as HVM, but additionally can use PV
56: drivers for efficiency. Therefore it is non-sensical for to have a
57: PVHVM dom0. See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
58:
59: There have been two PVH modes: original PVH and PVHv2. Original PVH
60: was based on PV mode and is no longer relevant at all. PVHv2 is
61: basically lightweight HVM with PV drivers. A critical feature of it
62: is that qemu is not needed; the hypervisor can do the emulation that
63: is required. Thus, a dom0 can be PVHv2.
64: The source code uses PVH and config files use pvh; this refers to PVHv2.
65: See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
66:
67: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
68: The dom0 can start one or more domUs. (Booting is explained in detail
69: in the dom0 section.)
70:
71: ## CPU Architecture
72:
73: Xen runs on x86_64 hardware (the NetBSD amd64 port).
74:
75: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
76:
77: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
78:
79: The domU can be i386PAE or amd64.
80: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
81:
82: ## Xen Versions
83:
84: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
85: xenkernel and xentools. We will refer only to the kernel versions,
86: but note that both packages must be installed together and must have
87: matching versions.
88:
89: Versions available in pkgsrc:
90:
91: [[!table data="""
92: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
93: 4.11 |xenkernel411 |x86_64 |No
94: 4.13 |xenkernel413 |x86_64 |No
95: """]]
96:
97: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
98:
99: Older Xen had a python-based management tool called xm, now replaced
100: by xl.
101:
102: ## NetBSD versions
103:
104: Xen has been supported in NetBSD for a long time, at least since 2005.
105: Initially Xen was PV only.
106:
107: NetBSD 8 and up support PV and HVM modes.
108:
109: Support for PVHVM and PVH is available only in NetBSD-current.
110:
111: NetBSD up to and including NetBSD 9 as a dom0 does not run SMP,
112: because some drivers are not yet safe for this. NetBSD-current
113: supports SMP in dom0.
114:
115: NetBSD, when run as a domU, can and does typically run SMP.
116:
117: Note that while Xen 4.13 is current, the kernel support is still
118: called XEN3, because the hypercall interface has not changed
119: significantly.
120:
121: # Creating a NetBSD dom0
122:
123: In order to install a NetBSD as a dom0, one first installs a normal
124: NetBSD system, and then pivot the install to a dom0 install by
125: changing the kernel and boot configuration.
126:
127: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
128: 512M it worked reliably. This does not make sense, but if you see
129: "not ELF" after Xen boots, try increasing dom0 RAM.
130:
131: ## Installation of NetBSD
132:
133: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
134: using Xen. Therefore, use the most recent release, or a build from
135: the most recent stable branch. Alternatively, use -current, being
136: mindful of all the usual caveats of lower stability of current, and
137: likely a bit more so.
138:
139: ## Installation of Xen
140:
141: ### Building Xen
142:
143: Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
144: Therefore, choose 4.13.
145: In the dom0, install xenkernel413 and xentools413 from pkgsrc.
146:
147: Once this is done, copy the Xen kernel from where pkgsrc puts it to
148: where the boot process will be able to find it:
149:
150: [[!template id=programlisting text="""
151: # cp -p /usr/pkg/xen413-kernel/xen.gz /
152: """]]
153:
154: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
155: kernel can either be taken from a local release build.sh run, compiled
156: manually, or downloaded from the NetBSD FTP, for example at:
157:
158: [[!template id=programlisting text="""
159: ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
160: """]]
161:
162: ### Configuring booting
163:
164: Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen,
165: adjusting for your root filesystem:
166:
167: [[!template id=filecontent name="/boot.cfg" text="""
168: menu=Xen:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc;multiboot /xen.gz dom0_mem=512M
169: menu=Xen single user:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc -s;multiboot /xen.gz dom0_mem=512M
170: """]]
171:
172: This specifies that the dom0 should have 512MB of ram, leaving the rest
173: to be allocated for domUs.
174:
175: NB: This says add, not replace, so that you will be able to more
176: easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may
177: want to set it as default. It is highly likely that you will have
178: trouble at some point, and keeping an up-to-date GENERIC for use in
179: fixing problems is the standard prudent approach.
180:
181: \todo Explain why rndseed is not set with Xen as part of the dom0
182: subconfiguration.
183:
184: Note that you are likely to have to set root= because the boot device
185: from /boot is not passed via Xen to the dom0 kernel. With one disk,
186: it will work, but e.g. plugging in USB disk to a machine with root on
187: wd0a causes boot to fail.
188:
189: Beware that userconf statements must be attached to the dom0 load, and
190: may not be at top-level, because then they would try to configure the
191: hypervisor, if there is a way to pass them via multiboot . It appears
192: that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very
193: early with a heap overflow.
194:
195: ### Console selection
196:
197: See boot_console(8). Understand that you should start from a place of
198: having console setup correct for booting GENERIC before trying to
199: configure Xen.
200:
201: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
202: equivalent, and this is passed on to /boot (where one typically does
203: not set the console). This configuration of bootxx_ffsv1 should also
204: be in place for Xen systems, to allow seeing messages from /boot and
205: use of a keyboard to select a line from the menu. And, one should
206: have a working boot path to GENERIC for rescue situations.
207:
208: With GENERIC, the boot options are passed on to /netbsd, but there is
209: currently no mechanism to pass these via multiboot to the hypervisor.
210: Thus, in addition to configuring the console in the boot blocks, one
211: must also configure it for Xen.
212:
213: By default, the hypervisor (Xen itself) will use some sort of vga
214: device as the console, much like GENERIC uses by default. The vga
215: console is relinquished at the conclusion of hypervisor boot, before
216: the dom0 is started. Xen when using a vga console does not process
217: console input.
218:
219: The hypervisor can be configured to use a serial port console, e.g.
220: [[!template id=filecontent name="/boot.cfg" text="""
221: menu=Xen:losad /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
222: """]]
223: This example uses the first serial port (Xen counts from 1; this is
224: what NetBSD would call com0), and sets speed and parity. (The dom0 is
225: then configured to use the same serial port in this example.)
226:
227: With the hypervisor configured for a serial console, it can get input,
228: and there is a notion of passing this input to the dom0. \todo
229: Explain why, if Xen has a serial console, the dom0 console is
230: typically also configured to open that same serial port, instead of
231: getting the passthrough input via the xen console.
232:
233: One also configures the console for the dom0. While one might expect
234: console=pc to be default, following behavior of GENERIC, a hasty read
235: of the code suggests there is no default and booting without a
236: selected console might lead to a panic. Also, there is merit in
237: explicit configuration. Therefore the standard approach is to place
238: console=pc as part of the load statement for the dom0 kernel, or
239: alternatively console=com0.
240:
241: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
242: exist), but this is not used as a console. It is used to obtain the
243: messages from the hypervisor's console; run `xl dmesg` to see them.
244:
245: ### Tuning
246:
247: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
248: to force only one vcpu to be provided (since NetBSD dom0 can't use
249: more) and to pin that vcpu to a physical CPU. Xen has
250: [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
251: and other than dom0 memory and max_vcpus, they are generally not
252: necessary.
253: \todo Revisit this advice with current.
254: \todo Explain if anyone has ever actually measured that this helps.
255:
256: ### rc.conf
257:
258: Ensure that the boot scripts installed in
259: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
260: have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
261: but a normal part of pkgsrc usage.)
262:
263: Set `xencommons=YES` in rc.conf:
264:
265: [[!template id=filecontent name="/etc/rc.conf" text="""
266: xencommons=YES
267: """]]
268:
269: \todo Recommend for/against xen-watchdog.
270:
271: ### Testing
272:
273: Now, reboot so that you are running a DOM0 kernel under Xen, rather
274: than GENERIC without Xen.
275:
276: Once the reboot is done, use `xl` to inspect Xen's boot messages,
277: available resources, and running domains. For example:
278:
279: [[!template id=programlisting text="""
280: # xl dmesg
281: ... xen's boot info ...
282: # xl info
283: ... available memory, etc ...
284: # xl list
285: Name Id Mem(MB) CPU State Time(s) Console
286: Domain-0 0 64 0 r---- 58.1
287: """]]
288:
289: Xen logs will be in /var/log/xen.
290:
291: ### Issues with xencommons
292:
293: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
294: domUs. It does not currently work to stop and start xenstored.
295: Certainly all domUs should be shutdown first, following the sort order
296: of the rc.d scripts. However, the dom0 sets up state with xenstored,
297: and is not notified when xenstored exits, leading to not recreating
298: the state when the new xenstored starts. Until there's a mechanism to
299: make this work, one should not expect to be able to restart xenstored
300: (and thus xencommons). There is currently no reason to expect that
301: this will get fixed any time soon.
302: \todo Confirm if this is still true in 2020.
303:
304: ## Xen-specific NetBSD issues
305:
306: There are (at least) two additional things different about NetBSD as a
307: dom0 kernel compared to hardware.
308:
309: One is that through NetBSD 9 the module ABI is different because some
310: of the #defines change, so there are separate sets of modules in
311: /stand. In NetBSD-current, there is only one set of modules.
312:
313: The other difference is that XEN3_DOM0 does not have exactly the same
314: options as GENERIC. While it is debatable whether or not this is a
315: bug, users should be aware of this and can simply add missing config
316: items if desired.
317:
318: Finally, there have been occasional reports of trouble with X11
319: servers in NetBSD as a dom0.
320:
321: ## Updating Xen in a dom0
322:
323: Basically, update the xenkernel and xentools packages and copy the new
324: Xen kernel into place, and reboot. This procedure should be usable to
325: update to a new Xen release, but the reader is reminded that having a
326: non-Xen boot methods was recommended earlier.
327:
328: ## Updating NetBSD in a dom0
329:
330: This is just like updating NetBSD on bare hardware, assuming the new
331: version supports the version of Xen you are running. Generally, one
332: replaces the kernel and reboots, and then overlays userland binaries
333: and adjusts `/etc`.
334:
335: Note that one should update both the non-Xen kernel typically used for
336: rescue purposes, as well as the DOM0 kernel used with Xen.
337:
338: ## anita (for testing NetBSD)
339:
340: With a NetBSD dom0, even without any domUs, one should be able to run
341: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
342: root, because anita must create a domU):
343:
344: [[!template id=programlisting text="""
345: anita --vmm=xl test file:///usr/obj/i386/
346: """]]
347:
348: # Unprivileged domains (domU)
349:
350: This section describes general concepts about domUs. It does not
351: address specific domU operating systems or how to install them. The
352: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
353: typically named so that the file name, domU name and the domU's host
354: name match.
355:
356: The domU is provided with CPU and memory by Xen, configured by the
357: dom0. The domU is provided with disk and network by the dom0,
358: mediated by Xen, and configured in the dom0.
359:
360: Entropy in domUs can be an issue; physical disks and network are on
361: the dom0. NetBSD's /dev/random system works, but is often challenged.
362:
363: ## Config files
364:
365: See /usr/pkg/share/examples/xen/xlexample* for a very small number of
366: examples for running GNU/Linux.
367:
368: The following is an example minimal domain configuration file. The domU
369: serves as a network file server.
370:
371: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
372: name = "domU-id"
373: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
374: memory = 1024
375: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
376: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
377: 'file:/n0/xen/foo-wd1,0x1,w' ]
378: """]]
379:
380: The domain will have name given in the `name` setting. The kernel has the
381: host/domU name in it, so that on the dom0 one can update the various
382: domUs independently. The `vif` line causes an interface to be provided,
383: with a specific mac address (do not reuse MAC addresses!), in bridge
384: mode. Two disks are provided, and they are both writable; the bits
385: are stored in files and Xen attaches them to a vnd(4) device in the
386: dom0 on domain creation. The system treats xbd0 as the boot device
387: without needing explicit configuration.
388:
389: There is not type line; that implicitly defines a pv domU. Otherwise,
390: one sets type to the lower-case version of the domU type in the table
391: above, e.g. `type = "hvm"`.
392:
393: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
394: that "xl create" takes the name of a config file, while other commands
395: take the name of a domain.
396:
397: Examples of commands:
398:
399: [[!template id=programlisting text="""
400: xl create /usr/pkg/etc/xen/foo
401: xl console domU-id
402: xl create -c /usr/pkg/etc/xen/foo
403: xl shutdown domU-id
404: xl list
405: """]]
406:
407: Typing `^]` will exit the console session. Shutting down a domain is
408: equivalent to pushing the power button; a NetBSD domU will receive a
409: power-press event and do a clean shutdown. Shutting down the dom0
410: will trigger controlled shutdowns of all configured domUs.
411:
412: ## CPU and memory
413:
414: A domain is provided with some number of vcpus, up to the number
415: of CPUs seen by the hypervisor. For a domU, it is controlled
416: from the config file by the "vcpus = N" directive.
417:
418: A domain is provided with memory; this is controlled in the config
419: file by "memory = N" (in megabytes). In the straightforward case, the
420: sum of the the memory allocated to the dom0 and all domUs must be less
421: than the available memory.
422:
423: ## Balloon driver
424:
425: Xen provides a `balloon` driver, which can be used to let domains use
426: more memory temporarily.
427:
428: \todo Explain how to set up a aystem to use the balloon scheme in a
429: useful manner.
430:
431: ## Virtual disks
432:
433: In domU config files, the disks are defined as a sequence of 3-tuples:
434:
435: * The first element is "method:/path/to/disk". Common methods are
436: "file:" for a file-backed vnd, and "phy:" for something that is already
437: a device, such as an LVM logical volume.
438:
439: * The second element is an artifact of how virtual disks are passed to
440: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
441: are given a device name to associate with the disk, and values like
442: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
443: as xbd0, the second as xbd1, and so on. However, xl demands a
444: second argument. The name given is converted to a major/minor by
445: calling stat(2) on the name in /dev and this is passed to the domU.
446: In the general case, the dom0 and domU can be different operating
447: systems, and it is an unwarranted assumption that they have consistent
448: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
449: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
450: for the second works fine and avoids this issue. For a GNU/Linux
451: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
452: /dev/hda1.
453:
454: * The third element is "w" for writable disks, and "r" for read-only
455: disks.
456:
457: Example:
458: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
459: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
460: """]]
461:
462: Note that NetBSD by default creates only vnd[0123]. If you need more
463: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
464: dom0.
465:
466: ## Virtual Networking
467:
468: Xen provides virtual Ethernets, each of which connects the dom0 and a
469: domU. For each virtual network, there is an interface "xvifN.M" in
470: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
471: The interfaces behave as if there is an Ethernet with two
472: adapters connected. From this primitive, one can construct various
473: configurations. We focus on two common and useful cases for which
474: there are existing scripts: bridging and NAT.
475:
476: With bridging (in the example above), the domU perceives itself to be
477: on the same network as the dom0. For server virtualization, this is
478: usually best. Bridging is accomplished by creating a bridge(4) device
479: and adding the dom0's physical interface and the various xvifN.0
480: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
481: config file. The bridge must be set up already in the dom0; an
482: example /etc/ifconfig.bridge0 is:
483:
484: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
485: create
486: up
487: !brconfig bridge0 add wm0
488: """]]
489:
490: With NAT, the domU perceives itself to be behind a NAT running on the
491: dom0. This is often appropriate when running Xen on a workstation.
492: TODO: NAT appears to be configured by "vif = [ '' ]".
493:
494: The MAC address specified is the one used for the interface in the new
495: domain. The interface in dom0 will use this address XOR'd with
496: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
497:
498: ## Starting domains automatically
499:
500: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
501: down cleanly on dom0 shutdown, add the following in rc.conf:
502:
503: [[!template id=filecontent name="/etc/rc.conf" text="""
504: xendomains="domU-netbsd domU-linux"
505: """]]
506:
507: # domU setup for specific systems
508:
509: Creating domUs is almost entirely independent of operating system. We
510: have already presented the basics of config files in the previous system.
511:
512: Of course, this section presumes that you have a working dom0.
513:
514: ## Creating a NetBSD PV domU
515:
516: See the earlier config file, and adjust memory. Decide on how much
517: storage you will provide, and prepare it (file or LVM).
518:
519: While the kernel will be obtained from the dom0 file system, the same
520: file should be present in the domU as /netbsd so that tools like
521: savecore(8) can work. (This is helpful but not necessary.)
522:
523: The kernel must be specifically built for Xen, to use PV interfacesas
524: a domU. NetBSD release builds provide the following kernels:
525:
526: i386 XEN3PAE_DOMU
527: amd64 XEN3_DOMU
528:
529: This will boot NetBSD, but this is not that useful if the disk is
530: empty. One approach is to unpack sets onto the disk outside of Xen
531: (by mounting it, just as you would prepare a physical disk for a
532: system you can't run the installer on).
533:
534: A second approach is to run an INSTALL kernel, which has a miniroot
535: and can load sets from the network. To do this, copy the INSTALL
536: kernel to / and change the kernel line in the config file to:
537:
538: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
539:
540: Then, start the domain as "xl create -c configfile".
541:
542: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
543: line should be used in the config file.
544:
545: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
546:
547: After booting the domain, the option to install via CDROM may be
548: selected. The CDROM device should be changed to `xbd1d`.
549:
550: Once done installing, "halt -p" the new domain (don't reboot or halt:
551: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
552: config file), switch the config file back to the XEN3_DOMU kernel,
553: and start the new domain again. Now it should be able to use "root on
554: xbd0a" and you should have a functional NetBSD domU.
555:
556: TODO: check if this is still accurate.
557: When the new domain is booting you'll see some warnings about *wscons*
558: and the pseudo-terminals. These can be fixed by editing the files
559: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
560: `/etc/ttys`, except *console*, like this:
561:
562: console "/usr/libexec/getty Pc" vt100 on secure
563: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
564: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
565: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
566: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
567:
568: Finally, all screens must be commented out from `/etc/wscons.conf`.
569:
570: One should also run `powerd` in a domU, but this should not need
571: configuring. With powerd, the domain will run a controlled shutdown
572: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
573: receiving a synthetic `power button pressed` signal. In 9 and
574: current, `powerd` is run by default under Xen kernels (or if ACPI is
575: present), and it can be added to rc.conf if not.
576:
577: It is not strictly necessary to have a kernel (as /netbsd) in the domU
578: file system. However, various programs (e.g. netstat) will use that
579: kernel to look up symbols to read from kernel virtual memory. If
580: /netbsd is not the running kernel, those lookups will fail. (This is
581: not really a Xen-specific issue, but because the domU kernel is
582: obtained from the dom0, it is far more likely to be out of sync or
583: missing with Xen.)
584:
585: Note that NetBSD by default creates only xbd[0123]. If you need more
586: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
587:
588: ## Creating a Linux PV domU
589:
590: Creating unprivileged Linux domains isn't much different from
591: unprivileged NetBSD domains, but there are some details to know.
592:
593: First, the second parameter passed to the disk declaration (the '0x1' in
594: the example below)
595:
596: disk = [ 'phy:/dev/wd0e,0x1,w' ]
597:
598: does matter to Linux. It wants a Linux device number here (e.g. 0x300
599: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
600: So, hda1 which has major 3 and minor 1 on a Linux system will have
601: device number 0x301. Alternatively, devices names can be used (hda,
602: hdb, ...) as xentools has a table to map these names to devices
603: numbers. To export a partition to a Linux guest we can use:
604:
605: disk = [ 'phy:/dev/wd0e,0x300,w' ]
606: root = "/dev/hda1 ro"
607:
608: and it will appear as /dev/hda on the Linux system, and be used as root
609: partition.
610:
611: To install the Linux system on the partition to be exported to the
612: guest domain, the following method can be used: install
613: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
614: that will be the root partition of your Linux domain, and mount it.
615: Then copy the files from a working Linux system, make adjustments in
616: `/etc` (fstab, network config). It should also be possible to extract
617: binary packages such as .rpm or .deb directly to the mounted partition
618: using the appropriate tool, possibly running under NetBSD's Linux
619: emulation. Once the file system has been populated, umount it. If
620: desirable, the file system can be converted to ext3 using tune2fs -j.
621: It should now be possible to boot the Linux guest domain, using one of
622: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
623:
624: To get the Linux console right, you need to add:
625:
626: extra = "xencons=tty1"
627:
628: to your configuration since not all Linux distributions auto-attach a
629: tty to the xen console.
630:
631: ## Creating a NetBSD HVM domU
632:
633: Use type='hvm', probably. Use a GENERIC kernel within the disk image.
634:
635: ## Creating a NetBSD PVH domU
636:
637: This only works with a current kernel in the domU.
638:
639: Use type='pvh'. Probably, use a GENERIC kernel within the disk image,
640: which in current has PV support.
641:
642: \todo Verify.
643:
644: \todo Verify if one can have current PVH domU on a 9 dom0.
645:
646: ## Creating a Solaris domU
647:
648: See possibly outdated
649: [Solaris domU instructions](/ports/xen/howto-solaris/).
650:
651: ## PCI passthrough: Using PCI devices in guest domains
652:
653: NB: PCI passthrough only works on some Xen versions and as of 2020 it
654: is not clear that it works on any version in pkgsrc. \todo Reports
655: confirming or denying this notion should be sent to port-xen@.
656:
657: The dom0 can give other domains access to selected PCI
658: devices. This can allow, for example, a non-privileged domain to have
659: access to a physical network interface or disk controller. However,
660: keep in mind that giving a domain access to a PCI device most likely
661: will give the domain read/write access to the whole physical memory,
662: as PCs don't have an IOMMU to restrict memory access to DMA-capable
663: device. Also, it's not possible to export ISA devices to non-dom0
664: domains, which means that the primary VGA adapter can't be exported.
665: A guest domain trying to access the VGA registers will panic.
666:
667: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
668: not been ported to later versions at this time.
669:
670: For a PCI device to be exported to a domU, is has to be attached to
671: the "pciback" driver in dom0. Devices passed to the dom0 via the
672: pciback.hide boot parameter will attach to "pciback" instead of the
673: usual driver. The list of devices is specified as "(bus:dev.func)",
674: where bus and dev are 2-digit hexadecimal numbers, and func a
675: single-digit number:
676:
677: pciback.hide=(00:0a.0)(00:06.0)
678:
679: pciback devices should show up in the dom0's boot messages, and the
680: devices should be listed in the `/kern/xen/pci` directory.
681:
682: PCI devices to be exported to a domU are listed in the "pci" array of
683: the domU's config file, with the format "0000:bus:dev.func".
684:
685: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
686:
687: In the domU an "xpci" device will show up, to which one or more pci
688: buses will attach. Then the PCI drivers will attach to PCI buses as
689: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
690: or any PCI drivers built in by default; you have to build your own
691: kernel to use PCI devices in a domU. Here's a kernel config example;
692: note that only the "xpci" lines are unusual.
693:
694: include "arch/i386/conf/XEN3_DOMU"
695:
696: # Add support for PCI buses to the XEN3_DOMU kernel
697: xpci* at xenbus ?
698: pci* at xpci ?
699:
700: # PCI USB controllers
701: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
702:
703: # USB bus support
704: usb* at uhci?
705:
706: # USB Hubs
707: uhub* at usb?
708: uhub* at uhub? port ? configuration ? interface ?
709:
710: # USB Mass Storage
711: umass* at uhub? port ? configuration ? interface ?
712: wd* at umass?
713: # SCSI controllers
714: ahc* at pci? dev ? function ? # Adaptec [23]94x, aic78x0 SCSI
715:
716: # SCSI bus support (for both ahc and umass)
717: scsibus* at scsi?
718:
719: # SCSI devices
720: sd* at scsibus? target ? lun ? # SCSI disk drives
721: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
722:
723:
724: # Miscellaneous Information
725:
726: ## Nesting under Linux KVM
727:
728: It is possible to run a Xen and a NetBSD dom0 under Linux KVM. One
729: can enable virtio in the dom0 for greater speed.
730:
731: ## Other nesting
732:
733: In theory, any full emulation should be able to run Xen and a NetBSD
734: dom0. The HOWTO does not currently have information about Xen XVM
735: mode, nvmm, qemu, Virtualbox, etc.
736:
737: ## NetBSD 5 as domU
738:
739: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
740: (However, NetBSD 5 systems should be updated to a supported version.)
741:
742: # NetBSD as a domU in a VPS
743:
744: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
745: hardware. This section explains how to deal with Xen in a domU as a
746: virtual private server where you do not control or have access to the
747: dom0. This is not intended to be an exhaustive list of VPS providers;
748: only a few are mentioned that specifically support NetBSD.
749:
750: VPS operators provide varying degrees of access and mechanisms for
751: configuration. The big issue is usually how one controls which kernel
752: is booted, because the kernel is nominally in the dom0 file system (to
753: which VPS users do not normally have access). A second issue is how
754: to install NetBSD.
755: A VPS user may want to compile a kernel for security updates, to run
756: npf, run IPsec, or any other reason why someone would want to change
757: their kernel.
758:
759: One approach is to have an administrative interface to upload a kernel,
760: or to select from a prepopulated list. Other approaches are pygrub
761: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
762: kernel from the domU file system. This is closer to a regular physical
763: computer, where someone who controls a machine can replace the kernel.
764:
765: A second issue is multiple CPUs. With NetBSD 6, domUs support
766: multiple vcpus, and it is typical for VPS providers to enable multiple
767: CPUs for NetBSD domUs.
768:
769: ## Complexities due to Xen changes
770:
771: Xen has many security advisories and people running Xen systems make
772: different choices.
773:
774: ### stub domains
775:
776: Some (Linux only?) dom0 systems use something called "stub domains" to
777: isolate qemu from the dom0 system, as a security and reliabilty
778: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
779: ends up using PIO for disks rather than DMA. Of course, all of this
780: is emulated, but emulated PIO is unusably slow. This problem is not
781: currently understood.
782:
783: ### Grant tables
784:
785: There are multiple versions of using grant tables, and some security
786: advisories have suggested disabling some versions. Some versions of
787: NetBSD apparently only use specific versions and this can lead to
788: "NetBSD current doesn't run on hosting provider X" situations.
789:
790: \todo Explain better.
791:
792: ## Boot methods
793:
794: ### pvgrub
795:
796: pvgrub is a version of grub that uses PV operations instead of BIOS
797: calls. It is booted from the dom0 as the domU kernel, and then reads
798: /grub/menu.lst and loads a kernel from the domU file system.
799:
800: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
801: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
802: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
803: page](http://www.panix.com/v-colo/grub.html), which describes only
804: Linux but should be updated to cover NetBSD :-).
805:
806: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
807: their own kernel. See then [prgmr.com NetBSD
808: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
809: (which is in need of updating).
810:
811: It appears that [grub's FFS
812: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
813: does not support all aspects of modern FFS, but there are also reports
814: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
815: partition for the kernel with the intent that grub can understand it,
816: which leads to /netbsd not being the actual kernel. One must remember
817: to update the special boot partition.
818:
819: ### pygrub
820:
821: pygrub runs in the dom0 and looks into the domU file system. This
822: implies that the domU must have a kernel in a file system in a format
823: known to pygrub.
824:
825: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
826: and is inherently less secure than pvgrub due to running inside dom0. For both these
827: reasons, pygrub should not be used, and is only still present so that
828: historical DomU images using it still work.
829:
830: As of 2014, pygrub seems to be of mostly historical
831: interest. New DomUs should use pvgrub.
832:
833: ## Specific Providers
834:
835: ### Amazon
836:
837: See the [Amazon EC2 page](/amazon_ec2/).
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