File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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xen: move netbsd info to netbsd section

    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: Older Xen had a python-based management tool called xm, now replaced
   96: by xl.
   98: ## NetBSD versions
  100: Xen has been supported in NetBSD for a long time, at least since 2005.
  101: Initially Xen was PV only.
  103: NetBSD 8 and up support PV and HVM modes.
  105: Support for PVHVM and PVH is available only in NetBSD-current.
  107: NetBSD as a dom0 does not run SMP, because some drivers are not yet
  108: safe for this.  \todo Link to more information about what needs work.
  110: NetBSD, when run as a domU, can and does typically run SMP.
  112: Note: NetBSD support is called XEN3.  However, it does support Xen 4,
  113: because the hypercall interface has remained identical.
  115: # Creating a dom0
  117: In order to install a NetBSD as a dom0, one must first install a normal
  118: NetBSD system, and then pivot the install to a dom0 install by changing
  119: the kernel and boot configuration.
  121: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  122: 512M it worked reliably.  This does not make sense, but if you see
  123: "not ELF" after Xen boots, try increasing dom0 RAM.
  125: ## Installation of NetBSD
  127: [Install NetBSD/amd64](/guide/inst/)
  128: just as you would if you were not using Xen.
  130: ## Installation of Xen
  132: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
  133: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  135: Once this is done, install the Xen kernel itself:
  137: [[!template id=programlisting text="""
  138: # cp /usr/pkg/xen48-kernel/xen.gz /
  139: """]]
  141: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
  142: can either be compiled manually, or downloaded from the NetBSD FTP, for
  143: example at:
  145: [[!template id=programlisting text="""
  147: """]]
  149: Add a line to /boot.cfg to boot Xen:
  151: [[!template id=filecontent name="/boot.cfg" text="""
  152: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  153: """]]
  155: This specifies that the dom0 should have 512MB of ram, leaving the rest
  156: to be allocated for domUs.  To use a serial console, use:
  158: [[!template id=filecontent name="/boot.cfg" text="""
  159: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  160: """]]
  162: which will use the first serial port for Xen (which counts starting
  163: from 1, unlike NetBSD which counts starting from 0), forcing
  164: speed/parity.  Because the NetBSD command line lacks a
  165: "console=pc" argument, it will use the default "xencons" console device,
  166: which directs the console I/O through Xen to the same console device Xen
  167: itself uses (in this case, the serial port).
  169: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  170: to force only one vcpu to be provided (since NetBSD dom0 can't use
  171: more) and to pin that vcpu to a physical CPU. Xen has
  172: [many boot options](,
  173: and other than dom0 memory and max_vcpus, they are generally not
  174: necessary.
  176: Copy the boot scripts into `/etc/rc.d`:
  178: [[!template id=programlisting text="""
  179: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
  180: """]]
  182: Enable `xencommons`:
  184: [[!template id=filecontent name="/etc/rc.conf" text="""
  185: xencommons=YES
  186: """]]
  188: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  189: than GENERIC without Xen.
  191: TODO: Recommend for/against xen-watchdog.
  193: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  194: available resources, and running domains.  For example:
  196: [[!template id=programlisting text="""
  197: # xl dmesg
  198: ... xen's boot info ...
  199: # xl info
  200: ... available memory, etc ...
  201: # xl list
  202: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  203: Domain-0           0       64    0  r----     58.1
  204: """]]
  206: Xen logs will be in /var/log/xen.
  208: ### Issues with xencommons
  210: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  211: domUs.  It does not currently work to stop and start xenstored.
  212: Certainly all domUs should be shutdown first, following the sort order
  213: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  214: and is not notified when xenstored exits, leading to not recreating
  215: the state when the new xenstored starts.  Until there's a mechanism to
  216: make this work, one should not expect to be able to restart xenstored
  217: (and thus xencommons).  There is currently no reason to expect that
  218: this will get fixed any time soon.
  220: ## anita (for testing NetBSD)
  222: With the setup so far, one should be able to run
  223: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  224: root, because anita must create a domU):
  226: [[!template id=programlisting text="""
  227: anita --vmm=xl test file:///usr/obj/i386/
  228: """]]
  230: ## Xen-specific NetBSD issues
  232: There are (at least) two additional things different about NetBSD as a
  233: dom0 kernel compared to hardware.
  235: One is that the module ABI is different because some of the #defines
  236: change, so one must build modules for Xen.  As of netbsd-7, the build
  237: system does this automatically.
  239: The other difference is that XEN3_DOM0 does not have exactly the same
  240: options as GENERIC.  While it is debatable whether or not this is a
  241: bug, users should be aware of this and can simply add missing config
  242: items if desired.
  244: ## Updating NetBSD in a dom0
  246: This is just like updating NetBSD on bare hardware, assuming the new
  247: version supports the version of Xen you are running.  Generally, one
  248: replaces the kernel and reboots, and then overlays userland binaries
  249: and adjusts `/etc`.
  251: Note that one must update both the non-Xen kernel typically used for
  252: rescue purposes and the DOM0 kernel used with Xen.
  254: ## Converting from grub to /boot
  256: These instructions were used to convert a system from
  257: grub to /boot.  The system was originally installed in February of
  258: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  259: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  260: 4.1 and grub, much like the message linked earlier in the grub
  261: section.
  263: [[!template id=programlisting text="""
  264: # Install MBR bootblocks on both disks.
  265: fdisk -i /dev/rwd0d
  266: fdisk -i /dev/rwd1d
  267: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  268: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  269: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  270: # Install secondary boot loader
  271: cp -p /usr/mdec/boot /
  272: # Create boot.cfg following earlier guidance:
  273: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  274: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  275: menu=GENERIC:boot
  276: menu=GENERIC single-user:boot -s
  277: menu=GENERIC.ok:boot netbsd.ok
  278: menu=GENERIC.ok single-user:boot netbsd.ok -s
  279: menu=Drop to boot prompt:prompt
  280: default=1
  281: timeout=30
  282: """]]
  284: ## Upgrading Xen versions
  286: Minor version upgrades are trivial.  Just rebuild/replace the
  287: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  288: references it), and reboot.
  290: #Unprivileged domains (domU)
  292: This section describes general concepts about domUs.  It does not
  293: address specific domU operating systems or how to install them.  The
  294: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  295: typically named so that the file name, domU name and the domU's host
  296: name match.
  298: The domU is provided with CPU and memory by Xen, configured by the
  299: dom0.  The domU is provided with disk and network by the dom0,
  300: mediated by Xen, and configured in the dom0.
  302: Entropy in domUs can be an issue; physical disks and network are on
  303: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  305: ## Config files
  307: See /usr/pkg/share/examples/xen/xlexample*
  308: for a small number of well-commented examples, mostly for running
  309: GNU/Linux.
  311: The following is an example minimal domain configuration file. The domU
  312: serves as a network file server.
  314: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  315: name = "domU-id"
  316: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  317: memory = 1024
  318: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  319: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  320:          'file:/n0/xen/foo-wd1,0x1,w' ]
  321: """]]
  323: The domain will have name given in the `name` setting.  The kernel has the
  324: host/domU name in it, so that on the dom0 one can update the various
  325: domUs independently.  The `vif` line causes an interface to be provided,
  326: with a specific mac address (do not reuse MAC addresses!), in bridge
  327: mode.  Two disks are provided, and they are both writable; the bits
  328: are stored in files and Xen attaches them to a vnd(4) device in the
  329: dom0 on domain creation.  The system treats xbd0 as the boot device
  330: without needing explicit configuration.
  332: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  333: that "xl create" takes the name of a config file, while other commands
  334: take the name of a domain.
  336: Examples of commands:
  338: [[!template id=programlisting text="""
  339: xl create /usr/pkg/etc/xen/foo
  340: xl console domU-id
  341: xl create -c /usr/pkg/etc/xen/foo
  342: xl shutdown domU-id
  343: xl list
  344: """]]
  346: Typing `^]` will exit the console session.  Shutting down a domain is
  347: equivalent to pushing the power button; a NetBSD domU will receive a
  348: power-press event and do a clean shutdown.  Shutting down the dom0
  349: will trigger controlled shutdowns of all configured domUs.
  351: ## CPU and memory
  353: A domain is provided with some number of vcpus, up to the number
  354: of CPUs seen by the hypervisor. For a domU, it is controlled
  355: from the config file by the "vcpus = N" directive.
  357: A domain is provided with memory; this is controlled in the config
  358: file by "memory = N" (in megabytes).  In the straightforward case, the
  359: sum of the the memory allocated to the dom0 and all domUs must be less
  360: than the available memory.
  362: Xen also provides a "balloon" driver, which can be used to let domains
  363: use more memory temporarily.
  365: ## Virtual disks
  367: In domU config files, the disks are defined as a sequence of 3-tuples:
  369:  * The first element is "method:/path/to/disk". Common methods are
  370:    "file:" for a file-backed vnd, and "phy:" for something that is already
  371:    a device, such as an LVM logical volume.
  373:  * The second element is an artifact of how virtual disks are passed to
  374:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  375:    are given a device name to associate with the disk, and values like
  376:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  377:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  378:    second argument.  The name given is converted to a major/minor by
  379:    calling stat(2) on the name in /dev and this is passed to the domU.
  380:    In the general case, the dom0 and domU can be different operating
  381:    systems, and it is an unwarranted assumption that they have consistent
  382:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  383:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  384:    for the second works fine and avoids this issue.  For a GNU/Linux
  385:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  386:    /dev/hda1.
  388:  * The third element is "w" for writable disks, and "r" for read-only
  389:    disks.
  391: Example:
  392: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  393: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  394: """]]
  396: Note that NetBSD by default creates only vnd[0123].  If you need more
  397: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  398: dom0.
  400: Note that NetBSD by default creates only xbd[0123].  If you need more
  401: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  403: Virtual Networking
  404: ------------------
  406: Xen provides virtual Ethernets, each of which connects the dom0 and a
  407: domU.  For each virtual network, there is an interface "xvifN.M" in
  408: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  409: The interfaces behave as if there is an Ethernet with two
  410: adapters connected.  From this primitive, one can construct various
  411: configurations.  We focus on two common and useful cases for which
  412: there are existing scripts: bridging and NAT.
  414: With bridging (in the example above), the domU perceives itself to be
  415: on the same network as the dom0.  For server virtualization, this is
  416: usually best.  Bridging is accomplished by creating a bridge(4) device
  417: and adding the dom0's physical interface and the various xvifN.0
  418: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  419: config file.  The bridge must be set up already in the dom0; an
  420: example /etc/ifconfig.bridge0 is:
  422: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  423: create
  424: up
  425: !brconfig bridge0 add wm0
  426: """]]
  428: With NAT, the domU perceives itself to be behind a NAT running on the
  429: dom0.  This is often appropriate when running Xen on a workstation.
  430: TODO: NAT appears to be configured by "vif = [ '' ]".
  432: The MAC address specified is the one used for the interface in the new
  433: domain.  The interface in dom0 will use this address XOR'd with
  434: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  436: Starting domains automatically
  437: ------------------------------
  439: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  440: down cleanly on dom0 shutdown, add the following in rc.conf:
  442: [[!template id=filecontent name="/etc/rc.conf" text="""
  443: xendomains="domU-netbsd domU-linux"
  444: """]]
  446: # Creating a domU
  448: Creating domUs is almost entirely independent of operating system.  We
  449: have already presented the basics of config files.  Note that you must
  450: have already completed the dom0 setup so that "xl list" works.
  452: Creating a NetBSD PV domU
  453: --------------------------
  455: See the earlier config file, and adjust memory.  Decide on how much
  456: storage you will provide, and prepare it (file or LVM).
  458: While the kernel will be obtained from the dom0 file system, the same
  459: file should be present in the domU as /netbsd so that tools like
  460: savecore(8) can work.   (This is helpful but not necessary.)
  462: The kernel must be specifically for Xen and for use as a domU.  The
  463: i386 and amd64 provide the following kernels:
  465:         i386 XEN3PAE_DOMU
  466:         amd64 XEN3_DOMU
  468: This will boot NetBSD, but this is not that useful if the disk is
  469: empty.  One approach is to unpack sets onto the disk outside of xen
  470: (by mounting it, just as you would prepare a physical disk for a
  471: system you can't run the installer on).
  473: A second approach is to run an INSTALL kernel, which has a miniroot
  474: and can load sets from the network.  To do this, copy the INSTALL
  475: kernel to / and change the kernel line in the config file to:
  477:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  479: Then, start the domain as "xl create -c configfile".
  481: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  482: line should be used in the config file.
  484:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  486: After booting the domain, the option to install via CDROM may be
  487: selected.  The CDROM device should be changed to `xbd1d`.
  489: Once done installing, "halt -p" the new domain (don't reboot or halt,
  490: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  491: config file), switch the config file back to the XEN3_DOMU kernel,
  492: and start the new domain again. Now it should be able to use "root on
  493: xbd0a" and you should have a, functional NetBSD domU.
  495: TODO: check if this is still accurate.
  496: When the new domain is booting you'll see some warnings about *wscons*
  497: and the pseudo-terminals. These can be fixed by editing the files
  498: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  499: `/etc/ttys`, except *console*, like this:
  501:     console "/usr/libexec/getty Pc"         vt100   on secure
  502:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  503:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  504:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  505:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  507: Finally, all screens must be commented out from `/etc/wscons.conf`.
  509: It is also desirable to add
  511:         powerd=YES
  513: in rc.conf. This way, the domain will be properly shut down if
  514: `xl shutdown -R` or `xl shutdown -H` is used on the dom0.
  515: \todo Check the translation to xl.
  517: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  518: file system.  However, various programs (e.g. netstat) will use that
  519: kernel to look up symbols to read from kernel virtual memory.  If
  520: /netbsd is not the running kernel, those lookups will fail.  (This is
  521: not really a Xen-specific issue, but because the domU kernel is
  522: obtained from the dom0, it is far more likely to be out of sync or
  523: missing with Xen.)
  525: Creating a Linux domU
  526: ---------------------
  528: Creating unprivileged Linux domains isn't much different from
  529: unprivileged NetBSD domains, but there are some details to know.
  531: First, the second parameter passed to the disk declaration (the '0x1' in
  532: the example below)
  534:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  536: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  537: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  538: So, hda1 which has major 3 and minor 1 on a Linux system will have
  539: device number 0x301.  Alternatively, devices names can be used (hda,
  540: hdb, ...)  as xentools has a table to map these names to devices
  541: numbers.  To export a partition to a Linux guest we can use:
  543:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  544:         root = "/dev/hda1 ro"
  546: and it will appear as /dev/hda on the Linux system, and be used as root
  547: partition.
  549: To install the Linux system on the partition to be exported to the
  550: guest domain, the following method can be used: install
  551: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  552: that will be the root partition of your Linux domain, and mount it.
  553: Then copy the files from a working Linux system, make adjustments in
  554: `/etc` (fstab, network config).  It should also be possible to extract
  555: binary packages such as .rpm or .deb directly to the mounted partition
  556: using the appropriate tool, possibly running under NetBSD's Linux
  557: emulation.  Once the file system has been populated, umount it.  If
  558: desirable, the file system can be converted to ext3 using tune2fs -j.
  559: It should now be possible to boot the Linux guest domain, using one of
  560: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  562: To get the Linux console right, you need to add:
  564:     extra = "xencons=tty1"
  566: to your configuration since not all Linux distributions auto-attach a
  567: tty to the xen console.
  569: ## Creating a NetBSD HVM domU
  571: Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
  573: ## Creating a NetBSD PVH domU
  575: Use type='pvh'.
  577: \todo Explain where the kernel comes from.
  580: Creating a Solaris domU
  581: -----------------------
  583: See possibly outdated
  584: [Solaris domU instructions](/ports/xen/howto-solaris/).
  587: PCI passthrough: Using PCI devices in guest domains
  588: ---------------------------------------------------
  590: NB: PCI passthrough only works on some Xen versions and as of 2020 it
  591: is not clear that it works on any version in pkgsrc.  Reports
  592: confirming or denying this notion should be sent to port-xen@.
  594: The dom0 can give other domains access to selected PCI
  595: devices. This can allow, for example, a non-privileged domain to have
  596: access to a physical network interface or disk controller.  However,
  597: keep in mind that giving a domain access to a PCI device most likely
  598: will give the domain read/write access to the whole physical memory,
  599: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  600: device.  Also, it's not possible to export ISA devices to non-dom0
  601: domains, which means that the primary VGA adapter can't be exported.
  602: A guest domain trying to access the VGA registers will panic.
  604: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  605: not been ported to later versions at this time.
  607: For a PCI device to be exported to a domU, is has to be attached to
  608: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  609: pciback.hide boot parameter will attach to "pciback" instead of the
  610: usual driver.  The list of devices is specified as "(bus:dev.func)",
  611: where bus and dev are 2-digit hexadecimal numbers, and func a
  612: single-digit number:
  614:         pciback.hide=(00:0a.0)(00:06.0)
  616: pciback devices should show up in the dom0's boot messages, and the
  617: devices should be listed in the `/kern/xen/pci` directory.
  619: PCI devices to be exported to a domU are listed in the "pci" array of
  620: the domU's config file, with the format "0000:bus:dev.func".
  622:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  624: In the domU an "xpci" device will show up, to which one or more pci
  625: buses will attach.  Then the PCI drivers will attach to PCI buses as
  626: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  627: or any PCI drivers built in by default; you have to build your own
  628: kernel to use PCI devices in a domU.  Here's a kernel config example;
  629: note that only the "xpci" lines are unusual.
  631:         include         "arch/i386/conf/XEN3_DOMU"
  633:         # Add support for PCI buses to the XEN3_DOMU kernel
  634:         xpci* at xenbus ?
  635:         pci* at xpci ?
  637:         # PCI USB controllers
  638:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  640:         # USB bus support
  641:         usb*    at uhci?
  643:         # USB Hubs
  644:         uhub*   at usb?
  645:         uhub*   at uhub? port ? configuration ? interface ?
  647:         # USB Mass Storage
  648:         umass*  at uhub? port ? configuration ? interface ?
  649:         wd*     at umass?
  650:         # SCSI controllers
  651:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  653:         # SCSI bus support (for both ahc and umass)
  654:         scsibus* at scsi?
  656:         # SCSI devices
  657:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  658:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  661: # Specific Issues
  663: ## domU
  665: [NetBSD 5 is known to panic.](
  666: (However, NetBSD 5 systems should be updated to a supported version.)
  668: # NetBSD as a domU in a VPS
  670: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  671: hardware.  This section explains how to deal with Xen in a domU as a
  672: virtual private server where you do not control or have access to the
  673: dom0.  This is not intended to be an exhaustive list of VPS providers;
  674: only a few are mentioned that specifically support NetBSD.
  676: VPS operators provide varying degrees of access and mechanisms for
  677: configuration.  The big issue is usually how one controls which kernel
  678: is booted, because the kernel is nominally in the dom0 file system (to
  679: which VPS users do not normally have access).  A second issue is how
  680: to install NetBSD.
  681: A VPS user may want to compile a kernel for security updates, to run
  682: npf, run IPsec, or any other reason why someone would want to change
  683: their kernel.
  685: One approach is to have an administrative interface to upload a kernel,
  686: or to select from a prepopulated list.  Other approaches are pygrub
  687: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  688: kernel from the domU file system.  This is closer to a regular physical
  689: computer, where someone who controls a machine can replace the kernel.
  691: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  692: multiple vcpus, and it is typical for VPS providers to enable multiple
  693: CPUs for NetBSD domUs.
  695: ## Complexities due to Xen changes
  697: Xen has many security advisories and people running Xen systems make
  698: different choices.
  700: ### stub domains
  702: Some (Linux only?) dom0 systems use something called "stub domains" to
  703: isolate qemu from the dom0 system, as a security and reliabilty
  704: mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
  705: ends up using PIO for disks rather than DMA.  Of course, all of this
  706: is emulated, but emulated PIO is unusably slow.  This problem is not
  707: currently understood.
  709: ### Grant tables
  711: There are multiple versions of using grant tables, and some security
  712: advisories have suggested disabling some versions.  Some versions of
  713: NetBSD apparently only use specific versions and this can lead to
  714: "NetBSD current doesn't run on hosting provider X" situations.
  716: \todo Explain better.
  718: ## Boot methods
  720: ### pvgrub
  722: pvgrub is a version of grub that uses PV operations instead of BIOS
  723: calls.  It is booted from the dom0 as the domU kernel, and then reads
  724: /grub/menu.lst and loads a kernel from the domU file system.
  726: [Panix]( lets users use pvgrub.  Panix reports
  727: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  728: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  729: page](, which describes only
  730: Linux but should be updated to cover NetBSD :-).
  732: []( also lets users with pvgrub to boot
  733: their own kernel.  See then [ NetBSD
  734: HOWTO](
  735: (which is in need of updating).
  737: It appears that [grub's FFS
  738: code](
  739: does not support all aspects of modern FFS, but there are also reports
  740: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  741: partition for the kernel with the intent that grub can understand it,
  742: which leads to /netbsd not being the actual kernel.  One must remember
  743: to update the special boot partition.
  745: ### pygrub
  747: pygrub runs in the dom0 and looks into the domU file system.  This
  748: implies that the domU must have a kernel in a file system in a format
  749: known to pygrub.
  751: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  752: and is inherently less secure than pvgrub due to running inside dom0. For both these
  753: reasons, pygrub should not be used, and is only still present so that
  754: historical DomU images using it still work.
  756: As of 2014, pygrub seems to be of mostly historical
  757: interest. New DomUs should use pvgrub.
  759: ## Specific Providers
  761: ### Amazon
  763: See the [Amazon EC2 page](/amazon_ec2/).

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