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: Versions of Xen, Styles, NetBSD
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: ## Guest Styles
31:
32: Xen supports different styles of guests.
33:
34: [[!table data="""
35: Style of guest |Supported by NetBSD
36: PV |Yes (dom0, domU)
37: HVM |Yes (domU)
38: PVHVM |current-only (domU)
39: PVH |current-only (domU, dom0 not yet)
40: """]]
41:
42: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
43: hardware directly, but instead makes hypercalls to the hypervisor; PV
44: guests must be specifically coded for Xen.
45: See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
46:
47: In HVM mode, no guest modification is required; however, hardware
48: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
49: The dom0 runs qemu to emulate hardware.
50:
51: In PVHVM mode, the guest runs as HVM, but additionally can use PV
52: drivers for efficiency.
53: See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
54:
55: There have been two PVH modes: original PVH and PVHv2. Original PVH
56: was based on PV mode and is no longer relevant at all. PVHv2 is
57: basically lightweight HVM with PV drivers. A critical feature of it
58: is that qemu is not needed; the hypervisor can do the emulation that
59: is required. Thus, a dom0 can be PVHv2.
60: The source code uses PVH and config files use pvh; this refers to PVHv2.
61: See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
62:
63:
64: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
65: The dom0 can start one or more domUs. (Booting is explained in detail
66: in the dom0 section.)
67:
68: ## CPU Architecture
69:
70: Xen runs on x86_64 hardware (the NetBSD amd64 port).
71:
72: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
73:
74: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
75:
76: The domU can be i386PAE or amd64.
77: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
78:
79: ## Xen Versions
80:
81: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
82: xenkernel and xentools. We will refer only to the kernel versions,
83: but note that both packages must be installed together and must have
84: matching versions.
85:
86: Versions available in pkgsrc:
87:
88: [[!table data="""
89: Xen Version |Package Name |Xen CPU Support |xm? |EOL'ed By Upstream
90: 4.11 |xenkernel411 |x86_64 | |No
91: 4.13 |xenkernel413 |x86_64 | |No
92: """]]
93:
94: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
95:
96: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
97:
98: [[!table data="""
99: Domain |Supports SMP
100: dom0 |No
101: domU |Yes
102: """]]
103:
104: Note: NetBSD support is called XEN3. However, it does support Xen 4,
105: because the hypercall interface has remained identical.
106:
107: Older Xen had a python-based management tool called xm, now replaced
108: by xl.
109:
110: # Creating a dom0
111:
112: In order to install a NetBSD as a dom0, one must first install a normal
113: NetBSD system, and then pivot the install to a dom0 install by changing
114: the kernel and boot configuration.
115:
116: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
117: 512M it worked reliably. This does not make sense, but if you see
118: "not ELF" after Xen boots, try increasing dom0 RAM.
119:
120: ## Installation of NetBSD
121:
122: [Install NetBSD/amd64](/guide/inst/)
123: just as you would if you were not using Xen.
124:
125: ## Installation of Xen
126:
127: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
128: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
129:
130: Once this is done, install the Xen kernel itself:
131:
132: [[!template id=programlisting text="""
133: # cp /usr/pkg/xen48-kernel/xen.gz /
134: """]]
135:
136: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
137: can either be compiled manually, or downloaded from the NetBSD FTP, for
138: example at:
139:
140: [[!template id=programlisting text="""
141: ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
142: """]]
143:
144: Add a line to /boot.cfg to boot Xen:
145:
146: [[!template id=filecontent name="/boot.cfg" text="""
147: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
148: """]]
149:
150: This specifies that the dom0 should have 512MB of ram, leaving the rest
151: to be allocated for domUs. To use a serial console, use:
152:
153: [[!template id=filecontent name="/boot.cfg" text="""
154: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
155: """]]
156:
157: which will use the first serial port for Xen (which counts starting
158: from 1, unlike NetBSD which counts starting from 0), forcing
159: speed/parity. Because the NetBSD command line lacks a
160: "console=pc" argument, it will use the default "xencons" console device,
161: which directs the console I/O through Xen to the same console device Xen
162: itself uses (in this case, the serial port).
163:
164: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
165: to force only one vcpu to be provided (since NetBSD dom0 can't use
166: more) and to pin that vcpu to a physical CPU. Xen has
167: [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
168: and other than dom0 memory and max_vcpus, they are generally not
169: necessary.
170:
171: Copy the boot scripts into `/etc/rc.d`:
172:
173: [[!template id=programlisting text="""
174: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
175: """]]
176:
177: Enable `xencommons`:
178:
179: [[!template id=filecontent name="/etc/rc.conf" text="""
180: xencommons=YES
181: """]]
182:
183: Now, reboot so that you are running a DOM0 kernel under Xen, rather
184: than GENERIC without Xen.
185:
186: TODO: Recommend for/against xen-watchdog.
187:
188: Once the reboot is done, use `xl` to inspect Xen's boot messages,
189: available resources, and running domains. For example:
190:
191: [[!template id=programlisting text="""
192: # xl dmesg
193: ... xen's boot info ...
194: # xl info
195: ... available memory, etc ...
196: # xl list
197: Name Id Mem(MB) CPU State Time(s) Console
198: Domain-0 0 64 0 r---- 58.1
199: """]]
200:
201: Xen logs will be in /var/log/xen.
202:
203: ### Issues with xencommons
204:
205: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
206: domUs. It does not currently work to stop and start xenstored.
207: Certainly all domUs should be shutdown first, following the sort order
208: of the rc.d scripts. However, the dom0 sets up state with xenstored,
209: and is not notified when xenstored exits, leading to not recreating
210: the state when the new xenstored starts. Until there's a mechanism to
211: make this work, one should not expect to be able to restart xenstored
212: (and thus xencommons). There is currently no reason to expect that
213: this will get fixed any time soon.
214:
215: ## anita (for testing NetBSD)
216:
217: With the setup so far, one should be able to run
218: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
219: root, because anita must create a domU):
220:
221: [[!template id=programlisting text="""
222: anita --vmm=xl test file:///usr/obj/i386/
223: """]]
224:
225: ## Xen-specific NetBSD issues
226:
227: There are (at least) two additional things different about NetBSD as a
228: dom0 kernel compared to hardware.
229:
230: One is that the module ABI is different because some of the #defines
231: change, so one must build modules for Xen. As of netbsd-7, the build
232: system does this automatically.
233:
234: The other difference is that XEN3_DOM0 does not have exactly the same
235: options as GENERIC. While it is debatable whether or not this is a
236: bug, users should be aware of this and can simply add missing config
237: items if desired.
238:
239: ## Updating NetBSD in a dom0
240:
241: This is just like updating NetBSD on bare hardware, assuming the new
242: version supports the version of Xen you are running. Generally, one
243: replaces the kernel and reboots, and then overlays userland binaries
244: and adjusts `/etc`.
245:
246: Note that one must update both the non-Xen kernel typically used for
247: rescue purposes and the DOM0 kernel used with Xen.
248:
249: ## Converting from grub to /boot
250:
251: These instructions were used to convert a system from
252: grub to /boot. The system was originally installed in February of
253: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
254: over time. Before these commands, it was running NetBSD 6 i386, Xen
255: 4.1 and grub, much like the message linked earlier in the grub
256: section.
257:
258: [[!template id=programlisting text="""
259: # Install MBR bootblocks on both disks.
260: fdisk -i /dev/rwd0d
261: fdisk -i /dev/rwd1d
262: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
263: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
264: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
265: # Install secondary boot loader
266: cp -p /usr/mdec/boot /
267: # Create boot.cfg following earlier guidance:
268: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
269: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
270: menu=GENERIC:boot
271: menu=GENERIC single-user:boot -s
272: menu=GENERIC.ok:boot netbsd.ok
273: menu=GENERIC.ok single-user:boot netbsd.ok -s
274: menu=Drop to boot prompt:prompt
275: default=1
276: timeout=30
277: """]]
278:
279: ## Upgrading Xen versions
280:
281: Minor version upgrades are trivial. Just rebuild/replace the
282: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
283: references it), and reboot.
284:
285: #Unprivileged domains (domU)
286:
287: This section describes general concepts about domUs. It does not
288: address specific domU operating systems or how to install them. The
289: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
290: typically named so that the file name, domU name and the domU's host
291: name match.
292:
293: The domU is provided with CPU and memory by Xen, configured by the
294: dom0. The domU is provided with disk and network by the dom0,
295: mediated by Xen, and configured in the dom0.
296:
297: Entropy in domUs can be an issue; physical disks and network are on
298: the dom0. NetBSD's /dev/random system works, but is often challenged.
299:
300: ## Config files
301:
302: See /usr/pkg/share/examples/xen/xlexample*
303: for a small number of well-commented examples, mostly for running
304: GNU/Linux.
305:
306: The following is an example minimal domain configuration file. The domU
307: serves as a network file server.
308:
309: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
310: name = "domU-id"
311: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
312: memory = 1024
313: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
314: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
315: 'file:/n0/xen/foo-wd1,0x1,w' ]
316: """]]
317:
318: The domain will have name given in the `name` setting. The kernel has the
319: host/domU name in it, so that on the dom0 one can update the various
320: domUs independently. The `vif` line causes an interface to be provided,
321: with a specific mac address (do not reuse MAC addresses!), in bridge
322: mode. Two disks are provided, and they are both writable; the bits
323: are stored in files and Xen attaches them to a vnd(4) device in the
324: dom0 on domain creation. The system treats xbd0 as the boot device
325: without needing explicit configuration.
326:
327: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
328: that "xl create" takes the name of a config file, while other commands
329: take the name of a domain.
330:
331: Examples of commands:
332:
333: [[!template id=programlisting text="""
334: xl create /usr/pkg/etc/xen/foo
335: xl console domU-id
336: xl create -c /usr/pkg/etc/xen/foo
337: xl shutdown domU-id
338: xl list
339: """]]
340:
341: Typing `^]` will exit the console session. Shutting down a domain is
342: equivalent to pushing the power button; a NetBSD domU will receive a
343: power-press event and do a clean shutdown. Shutting down the dom0
344: will trigger controlled shutdowns of all configured domUs.
345:
346: ## CPU and memory
347:
348: A domain is provided with some number of vcpus, up to the number
349: of CPUs seen by the hypervisor. For a domU, it is controlled
350: from the config file by the "vcpus = N" directive.
351:
352: A domain is provided with memory; this is controlled in the config
353: file by "memory = N" (in megabytes). In the straightforward case, the
354: sum of the the memory allocated to the dom0 and all domUs must be less
355: than the available memory.
356:
357: Xen also provides a "balloon" driver, which can be used to let domains
358: use more memory temporarily.
359:
360: ## Virtual disks
361:
362: In domU config files, the disks are defined as a sequence of 3-tuples:
363:
364: * The first element is "method:/path/to/disk". Common methods are
365: "file:" for a file-backed vnd, and "phy:" for something that is already
366: a device, such as an LVM logical volume.
367:
368: * The second element is an artifact of how virtual disks are passed to
369: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
370: are given a device name to associate with the disk, and values like
371: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
372: as xbd0, the second as xbd1, and so on. However, xl demands a
373: second argument. The name given is converted to a major/minor by
374: calling stat(2) on the name in /dev and this is passed to the domU.
375: In the general case, the dom0 and domU can be different operating
376: systems, and it is an unwarranted assumption that they have consistent
377: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
378: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
379: for the second works fine and avoids this issue. For a GNU/Linux
380: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
381: /dev/hda1.
382:
383: * The third element is "w" for writable disks, and "r" for read-only
384: disks.
385:
386: Example:
387: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
388: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
389: """]]
390:
391: Note that NetBSD by default creates only vnd[0123]. If you need more
392: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
393: dom0.
394:
395: Note that NetBSD by default creates only xbd[0123]. If you need more
396: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
397:
398: Virtual Networking
399: ------------------
400:
401: Xen provides virtual Ethernets, each of which connects the dom0 and a
402: domU. For each virtual network, there is an interface "xvifN.M" in
403: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
404: The interfaces behave as if there is an Ethernet with two
405: adapters connected. From this primitive, one can construct various
406: configurations. We focus on two common and useful cases for which
407: there are existing scripts: bridging and NAT.
408:
409: With bridging (in the example above), the domU perceives itself to be
410: on the same network as the dom0. For server virtualization, this is
411: usually best. Bridging is accomplished by creating a bridge(4) device
412: and adding the dom0's physical interface and the various xvifN.0
413: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
414: config file. The bridge must be set up already in the dom0; an
415: example /etc/ifconfig.bridge0 is:
416:
417: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
418: create
419: up
420: !brconfig bridge0 add wm0
421: """]]
422:
423: With NAT, the domU perceives itself to be behind a NAT running on the
424: dom0. This is often appropriate when running Xen on a workstation.
425: TODO: NAT appears to be configured by "vif = [ '' ]".
426:
427: The MAC address specified is the one used for the interface in the new
428: domain. The interface in dom0 will use this address XOR'd with
429: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
430:
431: Starting domains automatically
432: ------------------------------
433:
434: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
435: down cleanly on dom0 shutdown, add the following in rc.conf:
436:
437: [[!template id=filecontent name="/etc/rc.conf" text="""
438: xendomains="domU-netbsd domU-linux"
439: """]]
440:
441: # Creating a domU
442:
443: Creating domUs is almost entirely independent of operating system. We
444: have already presented the basics of config files. Note that you must
445: have already completed the dom0 setup so that "xl list" works.
446:
447: Creating a NetBSD PV domU
448: --------------------------
449:
450: See the earlier config file, and adjust memory. Decide on how much
451: storage you will provide, and prepare it (file or LVM).
452:
453: While the kernel will be obtained from the dom0 file system, the same
454: file should be present in the domU as /netbsd so that tools like
455: savecore(8) can work. (This is helpful but not necessary.)
456:
457: The kernel must be specifically for Xen and for use as a domU. The
458: i386 and amd64 provide the following kernels:
459:
460: i386 XEN3PAE_DOMU
461: amd64 XEN3_DOMU
462:
463: This will boot NetBSD, but this is not that useful if the disk is
464: empty. One approach is to unpack sets onto the disk outside of xen
465: (by mounting it, just as you would prepare a physical disk for a
466: system you can't run the installer on).
467:
468: A second approach is to run an INSTALL kernel, which has a miniroot
469: and can load sets from the network. To do this, copy the INSTALL
470: kernel to / and change the kernel line in the config file to:
471:
472: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
473:
474: Then, start the domain as "xl create -c configfile".
475:
476: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
477: line should be used in the config file.
478:
479: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
480:
481: After booting the domain, the option to install via CDROM may be
482: selected. The CDROM device should be changed to `xbd1d`.
483:
484: Once done installing, "halt -p" the new domain (don't reboot or halt,
485: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
486: config file), switch the config file back to the XEN3_DOMU kernel,
487: and start the new domain again. Now it should be able to use "root on
488: xbd0a" and you should have a, functional NetBSD domU.
489:
490: TODO: check if this is still accurate.
491: When the new domain is booting you'll see some warnings about *wscons*
492: and the pseudo-terminals. These can be fixed by editing the files
493: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
494: `/etc/ttys`, except *console*, like this:
495:
496: console "/usr/libexec/getty Pc" vt100 on secure
497: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
498: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
499: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
500: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
501:
502: Finally, all screens must be commented out from `/etc/wscons.conf`.
503:
504: It is also desirable to add
505:
506: powerd=YES
507:
508: in rc.conf. This way, the domain will be properly shut down if
509: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
510:
511: It is not strictly necessary to have a kernel (as /netbsd) in the domU
512: file system. However, various programs (e.g. netstat) will use that
513: kernel to look up symbols to read from kernel virtual memory. If
514: /netbsd is not the running kernel, those lookups will fail. (This is
515: not really a Xen-specific issue, but because the domU kernel is
516: obtained from the dom0, it is far more likely to be out of sync or
517: missing with Xen.)
518:
519: Creating a Linux domU
520: ---------------------
521:
522: Creating unprivileged Linux domains isn't much different from
523: unprivileged NetBSD domains, but there are some details to know.
524:
525: First, the second parameter passed to the disk declaration (the '0x1' in
526: the example below)
527:
528: disk = [ 'phy:/dev/wd0e,0x1,w' ]
529:
530: does matter to Linux. It wants a Linux device number here (e.g. 0x300
531: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
532: So, hda1 which has major 3 and minor 1 on a Linux system will have
533: device number 0x301. Alternatively, devices names can be used (hda,
534: hdb, ...) as xentools has a table to map these names to devices
535: numbers. To export a partition to a Linux guest we can use:
536:
537: disk = [ 'phy:/dev/wd0e,0x300,w' ]
538: root = "/dev/hda1 ro"
539:
540: and it will appear as /dev/hda on the Linux system, and be used as root
541: partition.
542:
543: To install the Linux system on the partition to be exported to the
544: guest domain, the following method can be used: install
545: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
546: that will be the root partition of your Linux domain, and mount it.
547: Then copy the files from a working Linux system, make adjustments in
548: `/etc` (fstab, network config). It should also be possible to extract
549: binary packages such as .rpm or .deb directly to the mounted partition
550: using the appropriate tool, possibly running under NetBSD's Linux
551: emulation. Once the file system has been populated, umount it. If
552: desirable, the file system can be converted to ext3 using tune2fs -j.
553: It should now be possible to boot the Linux guest domain, using one of
554: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
555:
556: To get the Linux console right, you need to add:
557:
558: extra = "xencons=tty1"
559:
560: to your configuration since not all Linux distributions auto-attach a
561: tty to the xen console.
562:
563: ## Creating a NetBSD HVM domU
564:
565: Use type='hmv', probably. Use a GENERIC kernel within the disk image.
566:
567: ## Creating a NetBSD PVH domU
568:
569: Use type='pvh'.
570:
571: \todo Explain where the kernel comes from.
572:
573:
574: Creating a Solaris domU
575: -----------------------
576:
577: See possibly outdated
578: [Solaris domU instructions](/ports/xen/howto-solaris/).
579:
580:
581: PCI passthrough: Using PCI devices in guest domains
582: ---------------------------------------------------
583:
584: NB: PCI passthrough only works on some Xen versions and as of 2020 it
585: is not clear that it works on any version in pkgsrc. Reports
586: confirming or denying this notion should be sent to port-xen@.
587:
588: The dom0 can give other domains access to selected PCI
589: devices. This can allow, for example, a non-privileged domain to have
590: access to a physical network interface or disk controller. However,
591: keep in mind that giving a domain access to a PCI device most likely
592: will give the domain read/write access to the whole physical memory,
593: as PCs don't have an IOMMU to restrict memory access to DMA-capable
594: device. Also, it's not possible to export ISA devices to non-dom0
595: domains, which means that the primary VGA adapter can't be exported.
596: A guest domain trying to access the VGA registers will panic.
597:
598: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
599: not been ported to later versions at this time.
600:
601: For a PCI device to be exported to a domU, is has to be attached to
602: the "pciback" driver in dom0. Devices passed to the dom0 via the
603: pciback.hide boot parameter will attach to "pciback" instead of the
604: usual driver. The list of devices is specified as "(bus:dev.func)",
605: where bus and dev are 2-digit hexadecimal numbers, and func a
606: single-digit number:
607:
608: pciback.hide=(00:0a.0)(00:06.0)
609:
610: pciback devices should show up in the dom0's boot messages, and the
611: devices should be listed in the `/kern/xen/pci` directory.
612:
613: PCI devices to be exported to a domU are listed in the "pci" array of
614: the domU's config file, with the format "0000:bus:dev.func".
615:
616: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
617:
618: In the domU an "xpci" device will show up, to which one or more pci
619: buses will attach. Then the PCI drivers will attach to PCI buses as
620: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
621: or any PCI drivers built in by default; you have to build your own
622: kernel to use PCI devices in a domU. Here's a kernel config example;
623: note that only the "xpci" lines are unusual.
624:
625: include "arch/i386/conf/XEN3_DOMU"
626:
627: # Add support for PCI buses to the XEN3_DOMU kernel
628: xpci* at xenbus ?
629: pci* at xpci ?
630:
631: # PCI USB controllers
632: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
633:
634: # USB bus support
635: usb* at uhci?
636:
637: # USB Hubs
638: uhub* at usb?
639: uhub* at uhub? port ? configuration ? interface ?
640:
641: # USB Mass Storage
642: umass* at uhub? port ? configuration ? interface ?
643: wd* at umass?
644: # SCSI controllers
645: ahc* at pci? dev ? function ? # Adaptec [23]94x, aic78x0 SCSI
646:
647: # SCSI bus support (for both ahc and umass)
648: scsibus* at scsi?
649:
650: # SCSI devices
651: sd* at scsibus? target ? lun ? # SCSI disk drives
652: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
653:
654:
655: # Specific Issues
656:
657: ## domU
658:
659: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
660: (However, NetBSD 5 systems should be updated to a supported version.)
661:
662: # NetBSD as a domU in a VPS
663:
664: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
665: hardware. This section explains how to deal with Xen in a domU as a
666: virtual private server where you do not control or have access to the
667: dom0. This is not intended to be an exhaustive list of VPS providers;
668: only a few are mentioned that specifically support NetBSD.
669:
670: VPS operators provide varying degrees of access and mechanisms for
671: configuration. The big issue is usually how one controls which kernel
672: is booted, because the kernel is nominally in the dom0 file system (to
673: which VPS users do not normally have access). A second issue is how
674: to install NetBSD.
675: A VPS user may want to compile a kernel for security updates, to run
676: npf, run IPsec, or any other reason why someone would want to change
677: their kernel.
678:
679: One approach is to have an administrative interface to upload a kernel,
680: or to select from a prepopulated list. Other approaches are pygrub
681: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
682: kernel from the domU file system. This is closer to a regular physical
683: computer, where someone who controls a machine can replace the kernel.
684:
685: A second issue is multiple CPUs. With NetBSD 6, domUs support
686: multiple vcpus, and it is typical for VPS providers to enable multiple
687: CPUs for NetBSD domUs.
688:
689: ## Complexities due to Xen changes
690:
691: Xen has many security advisories and people running Xen systems make
692: different choices.
693:
694: ### stub domains
695:
696: Some (Linux only?) dom0 systems use something called "stub domains" to
697: isolate qemu from the dom0 system, as a security and reliabilty
698: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
699: ends up using PIO for disks rather than DMA. Of course, all of this
700: is emulated, but emulated PIO is unusably slow. This problem is not
701: currently understood.
702:
703: ### Grant tables
704:
705: There are multiple versions of using grant tables, and some security
706: advisories have suggested disabling some versions. Some versions of
707: NetBSD apparently only use specific versions and this can lead to
708: "NetBSD current doesn't run on hosting provider X" situations.
709:
710: \todo Explain better.
711:
712: ## Boot methods
713:
714: ### pvgrub
715:
716: pvgrub is a version of grub that uses PV operations instead of BIOS
717: calls. It is booted from the dom0 as the domU kernel, and then reads
718: /grub/menu.lst and loads a kernel from the domU file system.
719:
720: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
721: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
722: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
723: page](http://www.panix.com/v-colo/grub.html), which describes only
724: Linux but should be updated to cover NetBSD :-).
725:
726: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
727: their own kernel. See then [prgmr.com NetBSD
728: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
729: (which is in need of updating).
730:
731: It appears that [grub's FFS
732: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
733: does not support all aspects of modern FFS, but there are also reports
734: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
735: partition for the kernel with the intent that grub can understand it,
736: which leads to /netbsd not being the actual kernel. One must remember
737: to update the special boot partition.
738:
739: ### pygrub
740:
741: pygrub runs in the dom0 and looks into the domU file system. This
742: implies that the domU must have a kernel in a file system in a format
743: known to pygrub.
744:
745: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
746: and is inherently less secure than pvgrub due to running inside dom0. For both these
747: reasons, pygrub should not be used, and is only still present so that
748: historical DomU images using it still work.
749:
750: As of 2014, pygrub seems to be of mostly historical
751: interest. New DomUs should use pvgrub.
752:
753: ## Specific Providers
754:
755: ### Amazon
756:
757: See the [Amazon EC2 page](/amazon_ec2/).
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