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    1: [[!meta title="Xen HowTo"]]
    3: Xen is a Type 1 hypervisor which supports running multiple guest operating
    4: systems on a single physical machine. One uses the Xen kernel to control the
    5: CPU, memory and console, a dom0 operating system which mediates access to
    6: other hardware (e.g., disks, network, USB), and one or more domU operating
    7: systems which operate in an unprivileged virtualized environment. IO requests
    8: from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
    9: fulfilled.
   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](
   16: [[!toc]]
   18: # Overview
   20: The basic concept of Xen is that the hypervisor (xenkernel) runs on
   21: the hardware, and runs a privileged domain ("dom0") that can access
   22: disks/networking/etc.  One then runs additonal unprivileged domains
   23: (each a "domU"), presumably to do something useful.
   25: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
   26: xen itself).  It also addresses how to run domUs in that environment,
   27: and how to deal with having a domU in a Xen environment run by someone
   28: else and/or not running NetBSD.
   30: ## Guest Styles
   32: Xen supports different styles of guests.
   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: """]]
   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](\)).
   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.
   51: In PVHVM mode, the guest runs as HVM, but additionally can use PV
   52: drivers for efficiency.
   53: See [PV on HVM](
   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)](\)_Domu).
   63: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   64: The dom0 can start one or more domUs.  (Booting is explained in detail
   65: in the dom0 section.)
   67: ## CPU Architecture
   69: Xen runs on x86_64 hardware (the NetBSD amd64 port).
   71: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   73: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   75: The domU can be i386PAE or amd64.
   76: i386PAE at one point was considered as [faster]( than amd64.
   78: ## Xen Versions
   80: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   81: xenkernel and xentools.  We will refer only to the kernel versions,
   82: but note that both packages must be installed together and must have
   83: matching versions.
   85: Versions available in pkgsrc:
   87: [[!table data="""
   88: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
   89: 4.11		|xenkernel411	|x86_64			|No
   90: 4.13		|xenkernel413	|x86_64			|No
   91: """]]
   93: See also the [Xen Security Advisory page](
   95: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
   97: [[!table data="""
   98: Domain		|Supports SMP
   99: dom0		|No
  100: domU		|Yes
  101: """]]
  103: Note: NetBSD support is called XEN3.  However, it does support Xen 4,
  104: because the hypercall interface has remained identical.
  106: Older Xen had a python-based management tool called xm, now replaced
  107: by xl.
  109: ## NetBSD versions
  111: Xen has been supported in NetBSD for a long time, at least since 2005.
  112: Initially Xen was PV only.
  114: NetBSD 8 and up support PV and HVM modes.
  116: Support for PVHVM and PVH is available only in NetBSD-current.
  118: # Creating a dom0
  120: In order to install a NetBSD as a dom0, one must first install a normal
  121: NetBSD system, and then pivot the install to a dom0 install by changing
  122: the kernel and boot configuration.
  124: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  125: 512M it worked reliably.  This does not make sense, but if you see
  126: "not ELF" after Xen boots, try increasing dom0 RAM.
  128: ## Installation of NetBSD
  130: [Install NetBSD/amd64](/guide/inst/)
  131: just as you would if you were not using Xen.
  133: ## Installation of Xen
  135: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
  136: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  138: Once this is done, install the Xen kernel itself:
  140: [[!template id=programlisting text="""
  141: # cp /usr/pkg/xen48-kernel/xen.gz /
  142: """]]
  144: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
  145: can either be compiled manually, or downloaded from the NetBSD FTP, for
  146: example at:
  148: [[!template id=programlisting text="""
  150: """]]
  152: Add a line to /boot.cfg to boot Xen:
  154: [[!template id=filecontent name="/boot.cfg" text="""
  155: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  156: """]]
  158: This specifies that the dom0 should have 512MB of ram, leaving the rest
  159: to be allocated for domUs.  To use a serial console, use:
  161: [[!template id=filecontent name="/boot.cfg" text="""
  162: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  163: """]]
  165: which will use the first serial port for Xen (which counts starting
  166: from 1, unlike NetBSD which counts starting from 0), forcing
  167: speed/parity.  Because the NetBSD command line lacks a
  168: "console=pc" argument, it will use the default "xencons" console device,
  169: which directs the console I/O through Xen to the same console device Xen
  170: itself uses (in this case, the serial port).
  172: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  173: to force only one vcpu to be provided (since NetBSD dom0 can't use
  174: more) and to pin that vcpu to a physical CPU. Xen has
  175: [many boot options](,
  176: and other than dom0 memory and max_vcpus, they are generally not
  177: necessary.
  179: Copy the boot scripts into `/etc/rc.d`:
  181: [[!template id=programlisting text="""
  182: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
  183: """]]
  185: Enable `xencommons`:
  187: [[!template id=filecontent name="/etc/rc.conf" text="""
  188: xencommons=YES
  189: """]]
  191: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  192: than GENERIC without Xen.
  194: TODO: Recommend for/against xen-watchdog.
  196: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  197: available resources, and running domains.  For example:
  199: [[!template id=programlisting text="""
  200: # xl dmesg
  201: ... xen's boot info ...
  202: # xl info
  203: ... available memory, etc ...
  204: # xl list
  205: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  206: Domain-0           0       64    0  r----     58.1
  207: """]]
  209: Xen logs will be in /var/log/xen.
  211: ### Issues with xencommons
  213: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  214: domUs.  It does not currently work to stop and start xenstored.
  215: Certainly all domUs should be shutdown first, following the sort order
  216: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  217: and is not notified when xenstored exits, leading to not recreating
  218: the state when the new xenstored starts.  Until there's a mechanism to
  219: make this work, one should not expect to be able to restart xenstored
  220: (and thus xencommons).  There is currently no reason to expect that
  221: this will get fixed any time soon.
  223: ## anita (for testing NetBSD)
  225: With the setup so far, one should be able to run
  226: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  227: root, because anita must create a domU):
  229: [[!template id=programlisting text="""
  230: anita --vmm=xl test file:///usr/obj/i386/
  231: """]]
  233: ## Xen-specific NetBSD issues
  235: There are (at least) two additional things different about NetBSD as a
  236: dom0 kernel compared to hardware.
  238: One is that the module ABI is different because some of the #defines
  239: change, so one must build modules for Xen.  As of netbsd-7, the build
  240: system does this automatically.
  242: The other difference is that XEN3_DOM0 does not have exactly the same
  243: options as GENERIC.  While it is debatable whether or not this is a
  244: bug, users should be aware of this and can simply add missing config
  245: items if desired.
  247: ## Updating NetBSD in a dom0
  249: This is just like updating NetBSD on bare hardware, assuming the new
  250: version supports the version of Xen you are running.  Generally, one
  251: replaces the kernel and reboots, and then overlays userland binaries
  252: and adjusts `/etc`.
  254: Note that one must update both the non-Xen kernel typically used for
  255: rescue purposes and the DOM0 kernel used with Xen.
  257: ## Converting from grub to /boot
  259: These instructions were used to convert a system from
  260: grub to /boot.  The system was originally installed in February of
  261: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  262: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  263: 4.1 and grub, much like the message linked earlier in the grub
  264: section.
  266: [[!template id=programlisting text="""
  267: # Install MBR bootblocks on both disks.
  268: fdisk -i /dev/rwd0d
  269: fdisk -i /dev/rwd1d
  270: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  271: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  272: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  273: # Install secondary boot loader
  274: cp -p /usr/mdec/boot /
  275: # Create boot.cfg following earlier guidance:
  276: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  277: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  278: menu=GENERIC:boot
  279: menu=GENERIC single-user:boot -s
  280: menu=GENERIC.ok:boot netbsd.ok
  281: menu=GENERIC.ok single-user:boot netbsd.ok -s
  282: menu=Drop to boot prompt:prompt
  283: default=1
  284: timeout=30
  285: """]]
  287: ## Upgrading Xen versions
  289: Minor version upgrades are trivial.  Just rebuild/replace the
  290: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  291: references it), and reboot.
  293: #Unprivileged domains (domU)
  295: This section describes general concepts about domUs.  It does not
  296: address specific domU operating systems or how to install them.  The
  297: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  298: typically named so that the file name, domU name and the domU's host
  299: name match.
  301: The domU is provided with CPU and memory by Xen, configured by the
  302: dom0.  The domU is provided with disk and network by the dom0,
  303: mediated by Xen, and configured in the dom0.
  305: Entropy in domUs can be an issue; physical disks and network are on
  306: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  308: ## Config files
  310: See /usr/pkg/share/examples/xen/xlexample*
  311: for a small number of well-commented examples, mostly for running
  312: GNU/Linux.
  314: The following is an example minimal domain configuration file. The domU
  315: serves as a network file server.
  317: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  318: name = "domU-id"
  319: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  320: memory = 1024
  321: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  322: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  323:          'file:/n0/xen/foo-wd1,0x1,w' ]
  324: """]]
  326: The domain will have name given in the `name` setting.  The kernel has the
  327: host/domU name in it, so that on the dom0 one can update the various
  328: domUs independently.  The `vif` line causes an interface to be provided,
  329: with a specific mac address (do not reuse MAC addresses!), in bridge
  330: mode.  Two disks are provided, and they are both writable; the bits
  331: are stored in files and Xen attaches them to a vnd(4) device in the
  332: dom0 on domain creation.  The system treats xbd0 as the boot device
  333: without needing explicit configuration.
  335: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  336: that "xl create" takes the name of a config file, while other commands
  337: take the name of a domain.
  339: Examples of commands:
  341: [[!template id=programlisting text="""
  342: xl create /usr/pkg/etc/xen/foo
  343: xl console domU-id
  344: xl create -c /usr/pkg/etc/xen/foo
  345: xl shutdown domU-id
  346: xl list
  347: """]]
  349: Typing `^]` will exit the console session.  Shutting down a domain is
  350: equivalent to pushing the power button; a NetBSD domU will receive a
  351: power-press event and do a clean shutdown.  Shutting down the dom0
  352: will trigger controlled shutdowns of all configured domUs.
  354: ## CPU and memory
  356: A domain is provided with some number of vcpus, up to the number
  357: of CPUs seen by the hypervisor. For a domU, it is controlled
  358: from the config file by the "vcpus = N" directive.
  360: A domain is provided with memory; this is controlled in the config
  361: file by "memory = N" (in megabytes).  In the straightforward case, the
  362: sum of the the memory allocated to the dom0 and all domUs must be less
  363: than the available memory.
  365: Xen also provides a "balloon" driver, which can be used to let domains
  366: use more memory temporarily.
  368: ## Virtual disks
  370: In domU config files, the disks are defined as a sequence of 3-tuples:
  372:  * The first element is "method:/path/to/disk". Common methods are
  373:    "file:" for a file-backed vnd, and "phy:" for something that is already
  374:    a device, such as an LVM logical volume.
  376:  * The second element is an artifact of how virtual disks are passed to
  377:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  378:    are given a device name to associate with the disk, and values like
  379:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  380:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  381:    second argument.  The name given is converted to a major/minor by
  382:    calling stat(2) on the name in /dev and this is passed to the domU.
  383:    In the general case, the dom0 and domU can be different operating
  384:    systems, and it is an unwarranted assumption that they have consistent
  385:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  386:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  387:    for the second works fine and avoids this issue.  For a GNU/Linux
  388:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  389:    /dev/hda1.
  391:  * The third element is "w" for writable disks, and "r" for read-only
  392:    disks.
  394: Example:
  395: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  396: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  397: """]]
  399: Note that NetBSD by default creates only vnd[0123].  If you need more
  400: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  401: dom0.
  403: Note that NetBSD by default creates only xbd[0123].  If you need more
  404: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  406: Virtual Networking
  407: ------------------
  409: Xen provides virtual Ethernets, each of which connects the dom0 and a
  410: domU.  For each virtual network, there is an interface "xvifN.M" in
  411: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  412: The interfaces behave as if there is an Ethernet with two
  413: adapters connected.  From this primitive, one can construct various
  414: configurations.  We focus on two common and useful cases for which
  415: there are existing scripts: bridging and NAT.
  417: With bridging (in the example above), the domU perceives itself to be
  418: on the same network as the dom0.  For server virtualization, this is
  419: usually best.  Bridging is accomplished by creating a bridge(4) device
  420: and adding the dom0's physical interface and the various xvifN.0
  421: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  422: config file.  The bridge must be set up already in the dom0; an
  423: example /etc/ifconfig.bridge0 is:
  425: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  426: create
  427: up
  428: !brconfig bridge0 add wm0
  429: """]]
  431: With NAT, the domU perceives itself to be behind a NAT running on the
  432: dom0.  This is often appropriate when running Xen on a workstation.
  433: TODO: NAT appears to be configured by "vif = [ '' ]".
  435: The MAC address specified is the one used for the interface in the new
  436: domain.  The interface in dom0 will use this address XOR'd with
  437: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  439: Starting domains automatically
  440: ------------------------------
  442: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  443: down cleanly on dom0 shutdown, add the following in rc.conf:
  445: [[!template id=filecontent name="/etc/rc.conf" text="""
  446: xendomains="domU-netbsd domU-linux"
  447: """]]
  449: # Creating a domU
  451: Creating domUs is almost entirely independent of operating system.  We
  452: have already presented the basics of config files.  Note that you must
  453: have already completed the dom0 setup so that "xl list" works.
  455: Creating a NetBSD PV domU
  456: --------------------------
  458: See the earlier config file, and adjust memory.  Decide on how much
  459: storage you will provide, and prepare it (file or LVM).
  461: While the kernel will be obtained from the dom0 file system, the same
  462: file should be present in the domU as /netbsd so that tools like
  463: savecore(8) can work.   (This is helpful but not necessary.)
  465: The kernel must be specifically for Xen and for use as a domU.  The
  466: i386 and amd64 provide the following kernels:
  468:         i386 XEN3PAE_DOMU
  469:         amd64 XEN3_DOMU
  471: This will boot NetBSD, but this is not that useful if the disk is
  472: empty.  One approach is to unpack sets onto the disk outside of xen
  473: (by mounting it, just as you would prepare a physical disk for a
  474: system you can't run the installer on).
  476: A second approach is to run an INSTALL kernel, which has a miniroot
  477: and can load sets from the network.  To do this, copy the INSTALL
  478: kernel to / and change the kernel line in the config file to:
  480:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  482: Then, start the domain as "xl create -c configfile".
  484: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  485: line should be used in the config file.
  487:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  489: After booting the domain, the option to install via CDROM may be
  490: selected.  The CDROM device should be changed to `xbd1d`.
  492: Once done installing, "halt -p" the new domain (don't reboot or halt,
  493: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  494: config file), switch the config file back to the XEN3_DOMU kernel,
  495: and start the new domain again. Now it should be able to use "root on
  496: xbd0a" and you should have a, functional NetBSD domU.
  498: TODO: check if this is still accurate.
  499: When the new domain is booting you'll see some warnings about *wscons*
  500: and the pseudo-terminals. These can be fixed by editing the files
  501: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  502: `/etc/ttys`, except *console*, like this:
  504:     console "/usr/libexec/getty Pc"         vt100   on secure
  505:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  506:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  507:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  508:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  510: Finally, all screens must be commented out from `/etc/wscons.conf`.
  512: It is also desirable to add
  514:         powerd=YES
  516: in rc.conf. This way, the domain will be properly shut down if
  517: `xl shutdown -R` or `xl shutdown -H` is used on the dom0.
  518: \todo Check the translation to xl.
  520: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  521: file system.  However, various programs (e.g. netstat) will use that
  522: kernel to look up symbols to read from kernel virtual memory.  If
  523: /netbsd is not the running kernel, those lookups will fail.  (This is
  524: not really a Xen-specific issue, but because the domU kernel is
  525: obtained from the dom0, it is far more likely to be out of sync or
  526: missing with Xen.)
  528: Creating a Linux domU
  529: ---------------------
  531: Creating unprivileged Linux domains isn't much different from
  532: unprivileged NetBSD domains, but there are some details to know.
  534: First, the second parameter passed to the disk declaration (the '0x1' in
  535: the example below)
  537:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  539: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  540: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  541: So, hda1 which has major 3 and minor 1 on a Linux system will have
  542: device number 0x301.  Alternatively, devices names can be used (hda,
  543: hdb, ...)  as xentools has a table to map these names to devices
  544: numbers.  To export a partition to a Linux guest we can use:
  546:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  547:         root = "/dev/hda1 ro"
  549: and it will appear as /dev/hda on the Linux system, and be used as root
  550: partition.
  552: To install the Linux system on the partition to be exported to the
  553: guest domain, the following method can be used: install
  554: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  555: that will be the root partition of your Linux domain, and mount it.
  556: Then copy the files from a working Linux system, make adjustments in
  557: `/etc` (fstab, network config).  It should also be possible to extract
  558: binary packages such as .rpm or .deb directly to the mounted partition
  559: using the appropriate tool, possibly running under NetBSD's Linux
  560: emulation.  Once the file system has been populated, umount it.  If
  561: desirable, the file system can be converted to ext3 using tune2fs -j.
  562: It should now be possible to boot the Linux guest domain, using one of
  563: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  565: To get the Linux console right, you need to add:
  567:     extra = "xencons=tty1"
  569: to your configuration since not all Linux distributions auto-attach a
  570: tty to the xen console.
  572: ## Creating a NetBSD HVM domU
  574: Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
  576: ## Creating a NetBSD PVH domU
  578: Use type='pvh'.
  580: \todo Explain where the kernel comes from.
  583: Creating a Solaris domU
  584: -----------------------
  586: See possibly outdated
  587: [Solaris domU instructions](/ports/xen/howto-solaris/).
  590: PCI passthrough: Using PCI devices in guest domains
  591: ---------------------------------------------------
  593: NB: PCI passthrough only works on some Xen versions and as of 2020 it
  594: is not clear that it works on any version in pkgsrc.  Reports
  595: confirming or denying this notion should be sent to port-xen@.
  597: The dom0 can give other domains access to selected PCI
  598: devices. This can allow, for example, a non-privileged domain to have
  599: access to a physical network interface or disk controller.  However,
  600: keep in mind that giving a domain access to a PCI device most likely
  601: will give the domain read/write access to the whole physical memory,
  602: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  603: device.  Also, it's not possible to export ISA devices to non-dom0
  604: domains, which means that the primary VGA adapter can't be exported.
  605: A guest domain trying to access the VGA registers will panic.
  607: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  608: not been ported to later versions at this time.
  610: For a PCI device to be exported to a domU, is has to be attached to
  611: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  612: pciback.hide boot parameter will attach to "pciback" instead of the
  613: usual driver.  The list of devices is specified as "(bus:dev.func)",
  614: where bus and dev are 2-digit hexadecimal numbers, and func a
  615: single-digit number:
  617:         pciback.hide=(00:0a.0)(00:06.0)
  619: pciback devices should show up in the dom0's boot messages, and the
  620: devices should be listed in the `/kern/xen/pci` directory.
  622: PCI devices to be exported to a domU are listed in the "pci" array of
  623: the domU's config file, with the format "0000:bus:dev.func".
  625:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  627: In the domU an "xpci" device will show up, to which one or more pci
  628: buses will attach.  Then the PCI drivers will attach to PCI buses as
  629: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  630: or any PCI drivers built in by default; you have to build your own
  631: kernel to use PCI devices in a domU.  Here's a kernel config example;
  632: note that only the "xpci" lines are unusual.
  634:         include         "arch/i386/conf/XEN3_DOMU"
  636:         # Add support for PCI buses to the XEN3_DOMU kernel
  637:         xpci* at xenbus ?
  638:         pci* at xpci ?
  640:         # PCI USB controllers
  641:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  643:         # USB bus support
  644:         usb*    at uhci?
  646:         # USB Hubs
  647:         uhub*   at usb?
  648:         uhub*   at uhub? port ? configuration ? interface ?
  650:         # USB Mass Storage
  651:         umass*  at uhub? port ? configuration ? interface ?
  652:         wd*     at umass?
  653:         # SCSI controllers
  654:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  656:         # SCSI bus support (for both ahc and umass)
  657:         scsibus* at scsi?
  659:         # SCSI devices
  660:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  661:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  664: # Specific Issues
  666: ## domU
  668: [NetBSD 5 is known to panic.](
  669: (However, NetBSD 5 systems should be updated to a supported version.)
  671: # NetBSD as a domU in a VPS
  673: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  674: hardware.  This section explains how to deal with Xen in a domU as a
  675: virtual private server where you do not control or have access to the
  676: dom0.  This is not intended to be an exhaustive list of VPS providers;
  677: only a few are mentioned that specifically support NetBSD.
  679: VPS operators provide varying degrees of access and mechanisms for
  680: configuration.  The big issue is usually how one controls which kernel
  681: is booted, because the kernel is nominally in the dom0 file system (to
  682: which VPS users do not normally have access).  A second issue is how
  683: to install NetBSD.
  684: A VPS user may want to compile a kernel for security updates, to run
  685: npf, run IPsec, or any other reason why someone would want to change
  686: their kernel.
  688: One approach is to have an administrative interface to upload a kernel,
  689: or to select from a prepopulated list.  Other approaches are pygrub
  690: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  691: kernel from the domU file system.  This is closer to a regular physical
  692: computer, where someone who controls a machine can replace the kernel.
  694: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  695: multiple vcpus, and it is typical for VPS providers to enable multiple
  696: CPUs for NetBSD domUs.
  698: ## Complexities due to Xen changes
  700: Xen has many security advisories and people running Xen systems make
  701: different choices.
  703: ### stub domains
  705: Some (Linux only?) dom0 systems use something called "stub domains" to
  706: isolate qemu from the dom0 system, as a security and reliabilty
  707: mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
  708: ends up using PIO for disks rather than DMA.  Of course, all of this
  709: is emulated, but emulated PIO is unusably slow.  This problem is not
  710: currently understood.
  712: ### Grant tables
  714: There are multiple versions of using grant tables, and some security
  715: advisories have suggested disabling some versions.  Some versions of
  716: NetBSD apparently only use specific versions and this can lead to
  717: "NetBSD current doesn't run on hosting provider X" situations.
  719: \todo Explain better.
  721: ## Boot methods
  723: ### pvgrub
  725: pvgrub is a version of grub that uses PV operations instead of BIOS
  726: calls.  It is booted from the dom0 as the domU kernel, and then reads
  727: /grub/menu.lst and loads a kernel from the domU file system.
  729: [Panix]( lets users use pvgrub.  Panix reports
  730: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  731: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  732: page](, which describes only
  733: Linux but should be updated to cover NetBSD :-).
  735: []( also lets users with pvgrub to boot
  736: their own kernel.  See then [ NetBSD
  737: HOWTO](
  738: (which is in need of updating).
  740: It appears that [grub's FFS
  741: code](
  742: does not support all aspects of modern FFS, but there are also reports
  743: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  744: partition for the kernel with the intent that grub can understand it,
  745: which leads to /netbsd not being the actual kernel.  One must remember
  746: to update the special boot partition.
  748: ### pygrub
  750: pygrub runs in the dom0 and looks into the domU file system.  This
  751: implies that the domU must have a kernel in a file system in a format
  752: known to pygrub.
  754: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  755: and is inherently less secure than pvgrub due to running inside dom0. For both these
  756: reasons, pygrub should not be used, and is only still present so that
  757: historical DomU images using it still work.
  759: As of 2014, pygrub seems to be of mostly historical
  760: interest. New DomUs should use pvgrub.
  762: ## Specific Providers
  764: ### Amazon
  766: See the [Amazon EC2 page](/amazon_ec2/).

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