Annotation of wikisrc/ports/xen/howto.mdwn, revision 1.205

1.203     gdt         1: [[!meta title="Xen Status and HowTo"]]
1.144     maxv        2: 
1.157     maxv        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.
1.12      gdt        10: 
1.203     gdt        11: This document provides status on what Xen things work on NetBSD
                     12: (upstream documentation might say something works if it works on some
                     13: particular Linux system).
                     14: 
                     15: This document is also a HOWTO that presumes a basic familiarity with
                     16: the Xen system architecture, with installing NetBSD on amd64 hardware,
                     17: and with installing software from pkgsrc.  See also the [Xen
1.182     gdt        18: website](http://www.xenproject.org/).
                     19: 
1.203     gdt        20: If this document says that something works, and you find that it does
                     21: not, it is best to ask on port-xen and if you are correct to file a
                     22: PR.
1.201     gdt        23: 
1.182     gdt        24: [[!toc]]
                     25: 
1.183     gdt        26: # Overview
1.182     gdt        27: 
                     28: The basic concept of Xen is that the hypervisor (xenkernel) runs on
                     29: the hardware, and runs a privileged domain ("dom0") that can access
1.204     gdt        30: disks/networking/etc.  One then runs additional unprivileged domains
1.182     gdt        31: (each a "domU"), presumably to do something useful.
                     32: 
                     33: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
                     34: xen itself).  It also addresses how to run domUs in that environment,
                     35: and how to deal with having a domU in a Xen environment run by someone
                     36: else and/or not running NetBSD.
                     37: 
1.186     gdt        38: There are many choices one can make; the HOWTO recommends the standard
                     39: approach and limits discussion of alternatives in many cases.
                     40: 
1.182     gdt        41: ## Guest Styles
                     42: 
1.205   ! gdt        43: Xen supports different styles of guests.  See
        !            44: https://wiki.xenproject.org/wiki/Virtualization_Spectrum for a
        !            45: discussion.
        !            46: 
        !            47: This table shows the styles, and if a NetBSD dom0 can run in that
        !            48: style, if a NetBSD dom0 can sypport that style of guest in a domU, and
        !            49: if NetBSD as a domU can support that style.
1.149     maxv       50: 
                     51: [[!table data="""
1.205   ! gdt        52: Style of guest |dom0 can be?   |dom0 can support?      |domU can be?
        !            53: PV             |yes            |yes                    |yes
        !            54: HVM            |N/A            |yes                    |yes
        !            55: PVHVM          |N/A            |yes                    |current only
        !            56: PVH            |not yet        |current only           |current only
1.149     maxv       57: """]]
                     58: 
1.205   ! gdt        59: In PV (paravirtualized) mode, the guest OS does not attempt to access
1.149     maxv       60: hardware directly, but instead makes hypercalls to the hypervisor; PV
1.205   ! gdt        61: guests must be specifically coded for Xen.  See
        !            62: [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
1.170     gdt        63: 
1.205   ! gdt        64: In HVM (Hardware Virtual Machine) mode, no guest modification is
        !            65: required.  However, hardware support is required, such as VT-x on
        !            66: Intel CPUs and SVM on AMD CPUs to assist with the processor emulation.
        !            67: The dom0 runs qemu to emulate hardware other than the processor.  It
        !            68: is therefore non-sensical to have an HVM dom0, because there is no
        !            69: underlying system to provide emulation.
1.170     gdt        70: 
1.205   ! gdt        71: In PVHVM mode, the guest runs as HVM, but additionally uses PV
1.199     gdt        72: drivers for efficiency.  Therefore it is non-sensical for to have a
                     73: PVHVM dom0.  See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
1.170     gdt        74: 
1.180     gdt        75: There have been two PVH modes: original PVH and PVHv2.  Original PVH
1.203     gdt        76: was based on PV mode and is no longer relevant at all.  Therefore
1.205   ! gdt        77: PVHv2 is written as PVH, here and elsewhere.  PVH is basically
        !            78: lightweight HVM with PV drivers.  A critical feature of it is that
        !            79: qemu is not needed; the hypervisor can do the emulation that is
        !            80: required.  Thus, a dom0 can be PVH.  The source code uses PVH and
        !            81: config files use pvh, but NB that this refers to PVHv2.  See
1.203     gdt        82: [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
1.180     gdt        83: 
1.205   ! gdt        84: At system boot, the dom0 kernel is loaded as a module with Xen as the
        !            85: kernel.  The dom0 can start one or more domUs.  (Booting is explained
        !            86: in detail in the dom0 section.)
1.12      gdt        87: 
1.182     gdt        88: ## CPU Architecture
                     89: 
                     90: Xen runs on x86_64 hardware (the NetBSD amd64 port).
                     91: 
                     92: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
                     93: 
                     94: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
1.1       mspo       95: 
1.204     gdt        96: The domU can be i386 PAE or amd64.
                     97: i386 PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
                     98: However, as of 2021 it is normal to use amd64 as the domU architecture, and use of i386 is dwindling.
1.150     maxv       99: 
1.182     gdt       100: ## Xen Versions
1.15      gdt       101: 
1.111     wiz       102: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
1.15      gdt       103: xenkernel and xentools.  We will refer only to the kernel versions,
                    104: but note that both packages must be installed together and must have
                    105: matching versions.
                    106: 
1.145     maxv      107: Versions available in pkgsrc:
1.85      gdt       108: 
1.145     maxv      109: [[!table data="""
1.184     gdt       110: Xen Version    |Package Name   |Xen CPU Support        |EOL'ed By Upstream
                    111: 4.11           |xenkernel411   |x86_64                 |No
                    112: 4.13           |xenkernel413   |x86_64                 |No
1.145     maxv      113: """]]
1.113     gdt       114: 
1.96      gdt       115: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
                    116: 
1.204     gdt       117: Older Xen had a python-based management tool called xm; this has been
                    118: replaced by xl.
1.166     gdt       119: 
1.183     gdt       120: ## NetBSD versions
                    121: 
                    122: Xen has been supported in NetBSD for a long time, at least since 2005.
                    123: Initially Xen was PV only.
                    124: 
1.204     gdt       125: NetBSD Xen has always supported PV, in both dom0 and domU; for a long
                    126: time this was the only way.  NetBSD >=8 as a dom0 supports HVM mode in
1.205   ! gdt       127: domUs.
1.203     gdt       128: 
                    129: Support for PVHVM and PVH is available only in NetBSD-current; this is
                    130: currently somewhat experimental, although PVHVM appears reasonably
                    131: solid.
                    132: 
                    133: NetBSD up to and including NetBSD 9 as a dom0 cannot safely run SMP.
                    134: Even if one added "options MULTIPROCESSOR" and configured multiple
                    135: vcpus, the kernel is likely to crash because of drivers without
                    136: adequate locking.
                    137: 
                    138: NetBSD-current supports SMP in dom0, and XEN3_DOM0 includes "options
                    139: MULTIPROCESSOR".
                    140: 
                    141: NetBSD (since NetBSD 6), when run as a domU, can run SMP, using
                    142: multiple CPUs if provided.  The XEN3_DOMU kernel is built
                    143: with "options MULITPROCESSOR".
1.185     gdt       144: 
1.191     gdt       145: Note that while Xen 4.13 is current, the kernel support is still
                    146: called XEN3, because the hypercall interface has not changed
                    147: significantly.
1.185     gdt       148: 
1.187     gdt       149: # Creating a NetBSD dom0
1.15      gdt       150: 
1.191     gdt       151: In order to install a NetBSD as a dom0, one first installs a normal
                    152: NetBSD system, and then pivot the install to a dom0 install by
                    153: changing the kernel and boot configuration.
1.15      gdt       154: 
1.142     gdt       155: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
                    156: 512M it worked reliably.  This does not make sense, but if you see
                    157: "not ELF" after Xen boots, try increasing dom0 RAM.
                    158: 
1.181     gdt       159: ## Installation of NetBSD
1.13      gdt       160: 
1.191     gdt       161: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
                    162: using Xen.  Therefore, use the most recent release, or a build from
                    163: the most recent stable branch.  Alternatively, use -current, being
                    164: mindful of all the usual caveats of lower stability of current, and
1.205   ! gdt       165: likely a bit more so.  Think about how you will provide storage for
        !           166: disk images.
1.1       mspo      167: 
1.181     gdt       168: ## Installation of Xen
1.1       mspo      169: 
1.191     gdt       170: ### Building Xen
                    171: 
1.205   ! gdt       172: Use the most recent version of Xen in pkgsrc, unless the DESCR says
        !           173: that it is not suitable.  Therefore, choose 4.13.  In the dom0,
        !           174: install xenkernel413 and xentools413 from pkgsrc.
1.155     maxv      175: 
1.186     gdt       176: Once this is done, copy the Xen kernel from where pkgsrc puts it to
                    177: where the boot process will be able to find it:
1.155     maxv      178: 
                    179: [[!template id=programlisting text="""
1.186     gdt       180: # cp -p /usr/pkg/xen413-kernel/xen.gz /
1.155     maxv      181: """]]
                    182: 
1.191     gdt       183: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
                    184: kernel can either be taken from a local release build.sh run, compiled
                    185: manually, or downloaded from the NetBSD FTP, for example at:
1.159     maxv      186: 
                    187: [[!template id=programlisting text="""
1.186     gdt       188: ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
1.159     maxv      189: """]]
1.20      gdt       190: 
1.191     gdt       191: ### Configuring booting
                    192: 
1.198     gdt       193: Read boot.cfg(8) carefully.  Add lines to /boot.cfg to boot Xen,
                    194: adjusting for your root filesystem:
1.20      gdt       195: 
1.157     maxv      196: [[!template id=filecontent name="/boot.cfg" text="""
1.198     gdt       197: menu=Xen:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc;multiboot /xen.gz dom0_mem=512M
                    198: menu=Xen single user:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc -s;multiboot /xen.gz dom0_mem=512M
1.152     maxv      199: """]]
1.20      gdt       200: 
1.159     maxv      201: This specifies that the dom0 should have 512MB of ram, leaving the rest
1.187     gdt       202: to be allocated for domUs.
                    203: 
1.191     gdt       204: NB: This says add, not replace, so that you will be able to more
                    205: easily boot a NetBSD kernel without Xen.  Once Xen boots ok, you may
                    206: want to set it as default.  It is highly likely that you will have
                    207: trouble at some point, and keeping an up-to-date GENERIC for use in
                    208: fixing problems is the standard prudent approach.
                    209: 
1.194     gdt       210: \todo Explain why rndseed is not set with Xen as part of the dom0
                    211: subconfiguration.
                    212: 
1.198     gdt       213: Note that you are likely to have to set root= because the boot device
                    214: from /boot is not passed via Xen to the dom0 kernel.  With one disk,
                    215: it will work, but e.g. plugging in USB disk to a machine with root on
                    216: wd0a causes boot to fail.
                    217: 
1.195     gdt       218: Beware that userconf statements must be attached to the dom0 load, and
                    219: may not be at top-level, because then they would try to configure the
1.205   ! gdt       220: hypervisor, if there is a way to pass them via multiboot.  It appears
1.195     gdt       221: that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very
                    222: early with a heap overflow.
                    223: 
1.191     gdt       224: ### Console selection
                    225: 
                    226: See boot_console(8).  Understand that you should start from a place of
                    227: having console setup correct for booting GENERIC before trying to
                    228: configure Xen.
                    229: 
1.193     gdt       230: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
                    231: equivalent, and this is passed on to /boot (where one typically does
                    232: not set the console).  This configuration of bootxx_ffsv1 should also
                    233: be in place for Xen systems, to allow seeing messages from /boot and
                    234: use of a keyboard to select a line from the menu.  And, one should
                    235: have a working boot path to GENERIC for rescue situations.
                    236: 
                    237: With GENERIC, the boot options are passed on to /netbsd, but there is
                    238: currently no mechanism to pass these via multiboot to the hypervisor.
                    239: Thus, in addition to configuring the console in the boot blocks, one
                    240: must also configure it for Xen.
                    241: 
                    242: By default, the hypervisor (Xen itself) will use some sort of vga
                    243: device as the console, much like GENERIC uses by default.  The vga
                    244: console is relinquished at the conclusion of hypervisor boot, before
1.194     gdt       245: the dom0 is started.  Xen when using a vga console does not process
                    246: console input.
1.77      gdt       247: 
1.193     gdt       248: The hypervisor can be configured to use a serial port console, e.g.
1.157     maxv      249: [[!template id=filecontent name="/boot.cfg" text="""
1.202     gson      250: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
1.152     maxv      251: """]]
1.194     gdt       252: This example uses the first serial port (Xen counts from 1; this is
1.193     gdt       253: what NetBSD would call com0), and sets speed and parity.  (The dom0 is
                    254: then configured to use the same serial port in this example.)
                    255: 
1.194     gdt       256: With the hypervisor configured for a serial console, it can get input,
                    257: and there is a notion of passing this input to the dom0.  \todo
                    258: Explain why, if Xen has a serial console, the dom0 console is
                    259: typically also configured to open that same serial port, instead of
                    260: getting the passthrough input via the xen console.
                    261: 
1.193     gdt       262: One also configures the console for the dom0.  While one might expect
                    263: console=pc to be default, following behavior of GENERIC, a hasty read
                    264: of the code suggests there is no default and booting without a
                    265: selected console might lead to a panic.  Also, there is merit in
                    266: explicit configuration.  Therefore the standard approach is to place
                    267: console=pc as part of the load statement for the dom0 kernel, or
                    268: alternatively console=com0.
                    269: 
                    270: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
                    271: exist), but this is not used as a console.  It is used to obtain the
                    272: messages from the hypervisor's console; run `xl dmesg` to see them.
1.191     gdt       273: 
                    274: ### Tuning
                    275: 
1.205   ! gdt       276: In an attempt to add performance, one can also add `dom0_max_vcpus=1
        !           277: dom0_vcpus_pin`, to force only one vcpu to be provided (since NetBSD
        !           278: dom0 can't use more) and to pin that vcpu to a physical CPU. Xen has
        !           279: [many boot
        !           280: options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
1.111     wiz       281: and other than dom0 memory and max_vcpus, they are generally not
1.93      gdt       282: necessary.
1.205   ! gdt       283: 
1.191     gdt       284: \todo Revisit this advice with current.
                    285: \todo Explain if anyone has ever actually measured that this helps.
                    286: 
                    287: ### rc.conf
1.93      gdt       288: 
1.186     gdt       289: Ensure that the boot scripts installed in
                    290: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
                    291: have `PKG_RCD_SCRIPTS=yes`, or manually.  (This is not special to Xen,
                    292: but a normal part of pkgsrc usage.)
1.159     maxv      293: 
1.186     gdt       294: Set `xencommons=YES` in rc.conf:
1.31      gdt       295: 
1.157     maxv      296: [[!template id=filecontent name="/etc/rc.conf" text="""
1.152     maxv      297: xencommons=YES
                    298: """]]
1.31      gdt       299: 
1.187     gdt       300: \todo Recommend for/against xen-watchdog.
                    301: 
1.191     gdt       302: ### Testing
                    303: 
1.158     maxv      304: Now, reboot so that you are running a DOM0 kernel under Xen, rather
                    305: than GENERIC without Xen.
1.157     maxv      306: 
1.158     maxv      307: Once the reboot is done, use `xl` to inspect Xen's boot messages,
1.157     maxv      308: available resources, and running domains.  For example:
1.34      gdt       309: 
1.153     maxv      310: [[!template id=programlisting text="""
                    311: # xl dmesg
                    312: ... xen's boot info ...
                    313: # xl info
                    314: ... available memory, etc ...
                    315: # xl list
                    316: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
                    317: Domain-0           0       64    0  r----     58.1
                    318: """]]
                    319: 
                    320: Xen logs will be in /var/log/xen.
1.33      gdt       321: 
1.88      gdt       322: ### Issues with xencommons
                    323: 
1.157     maxv      324: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
1.88      gdt       325: domUs.  It does not currently work to stop and start xenstored.
                    326: Certainly all domUs should be shutdown first, following the sort order
                    327: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
                    328: and is not notified when xenstored exits, leading to not recreating
                    329: the state when the new xenstored starts.  Until there's a mechanism to
                    330: make this work, one should not expect to be able to restart xenstored
                    331: (and thus xencommons).  There is currently no reason to expect that
                    332: this will get fixed any time soon.
1.187     gdt       333: \todo Confirm if this is still true in 2020.
1.82      gdt       334: 
1.181     gdt       335: ## Xen-specific NetBSD issues
1.40      gdt       336: 
                    337: There are (at least) two additional things different about NetBSD as a
                    338: dom0 kernel compared to hardware.
                    339: 
1.191     gdt       340: One is that through NetBSD 9 the module ABI is different because some
                    341: of the #defines change, so there are separate sets of modules in
1.205   ! gdt       342: /stand.  (Further, zfs in Xen is troubled because of differing
        !           343: MAXPHYS; see the zfs howto for more.)  In NetBSD-current, there is
        !           344: only one set of modules.
1.40      gdt       345: 
                    346: The other difference is that XEN3_DOM0 does not have exactly the same
1.205   ! gdt       347: options as GENERIC.  While this is roughly agreed to be in large part
        !           348: a bug, users should be aware of this and can simply add missing config
1.40      gdt       349: items if desired.
                    350: 
1.187     gdt       351: Finally, there have been occasional reports of trouble with X11
1.205   ! gdt       352: servers in NetBSD as a dom0.  Some hardware support is intentionally
        !           353: disabled in XEN3_DOM0.
1.187     gdt       354: 
                    355: ## Updating Xen in a dom0
                    356: 
                    357: Basically, update the xenkernel and xentools packages and copy the new
                    358: Xen kernel into place, and reboot.  This procedure should be usable to
                    359: update to a new Xen release, but the reader is reminded that having a
                    360: non-Xen boot methods was recommended earlier.
                    361: 
1.181     gdt       362: ## Updating NetBSD in a dom0
1.15      gdt       363: 
                    364: This is just like updating NetBSD on bare hardware, assuming the new
                    365: version supports the version of Xen you are running.  Generally, one
                    366: replaces the kernel and reboots, and then overlays userland binaries
1.157     maxv      367: and adjusts `/etc`.
1.15      gdt       368: 
1.191     gdt       369: Note that one should update both the non-Xen kernel typically used for
                    370: rescue purposes, as well as the DOM0 kernel used with Xen.
1.15      gdt       371: 
1.187     gdt       372: ## anita (for testing NetBSD)
                    373: 
1.205   ! gdt       374: With a NetBSD dom0, even without any domUs, one can run anita (see
        !           375: pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as root,
        !           376: because anita must create a domU):
1.187     gdt       377: 
                    378: [[!template id=programlisting text="""
                    379: anita --vmm=xl test file:///usr/obj/i386/
                    380: """]]
                    381: 
                    382: # Unprivileged domains (domU)
1.28      gdt       383: 
                    384: This section describes general concepts about domUs.  It does not
1.33      gdt       385: address specific domU operating systems or how to install them.  The
1.157     maxv      386: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
1.60      wiki      387: typically named so that the file name, domU name and the domU's host
1.33      gdt       388: name match.
                    389: 
1.111     wiz       390: The domU is provided with CPU and memory by Xen, configured by the
1.33      gdt       391: dom0.  The domU is provided with disk and network by the dom0,
                    392: mediated by Xen, and configured in the dom0.
                    393: 
                    394: Entropy in domUs can be an issue; physical disks and network are on
                    395: the dom0.  NetBSD's /dev/random system works, but is often challenged.
                    396: 
1.181     gdt       397: ## Config files
1.48      gdt       398: 
1.200     gdt       399: See /usr/pkg/share/examples/xen/xlexample* for a very small number of
                    400: examples for running GNU/Linux.
1.48      gdt       401: 
1.205   ! gdt       402: The following is an example minimal domain configuration file.  The
        !           403: domU serves as a network file server.
1.157     maxv      404: 
                    405: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
                    406: name = "domU-id"
                    407: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
                    408: memory = 1024
                    409: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
                    410: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
                    411:          'file:/n0/xen/foo-wd1,0x1,w' ]
                    412: """]]
1.48      gdt       413: 
1.157     maxv      414: The domain will have name given in the `name` setting.  The kernel has the
1.48      gdt       415: host/domU name in it, so that on the dom0 one can update the various
1.157     maxv      416: domUs independently.  The `vif` line causes an interface to be provided,
1.48      gdt       417: with a specific mac address (do not reuse MAC addresses!), in bridge
                    418: mode.  Two disks are provided, and they are both writable; the bits
                    419: are stored in files and Xen attaches them to a vnd(4) device in the
1.111     wiz       420: dom0 on domain creation.  The system treats xbd0 as the boot device
1.48      gdt       421: without needing explicit configuration.
                    422: 
1.205   ! gdt       423: There is not a type line; that implicitly defines a pv domU.
        !           424: Otherwise, one sets type to the lower-case version of the domU type in
        !           425: the table above; see later sections.
1.187     gdt       426: 
1.163     gson      427: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
1.157     maxv      428: that "xl create" takes the name of a config file, while other commands
                    429: take the name of a domain.
                    430: 
                    431: Examples of commands:
1.48      gdt       432: 
1.157     maxv      433: [[!template id=programlisting text="""
1.163     gson      434: xl create /usr/pkg/etc/xen/foo
                    435: xl console domU-id
                    436: xl create -c /usr/pkg/etc/xen/foo
                    437: xl shutdown domU-id
1.157     maxv      438: xl list
                    439: """]]
                    440: 
                    441: Typing `^]` will exit the console session.  Shutting down a domain is
1.48      gdt       442: equivalent to pushing the power button; a NetBSD domU will receive a
                    443: power-press event and do a clean shutdown.  Shutting down the dom0
                    444: will trigger controlled shutdowns of all configured domUs.
                    445: 
1.181     gdt       446: ## CPU and memory
1.33      gdt       447: 
1.205   ! gdt       448: A domain is provided with some number of vcpus; any domain can have up
        !           449: to the number of CPUs seen by the hypervisor. For a domU, it is
        !           450: controlled from the config file by the "vcpus = N" directive.  It is
        !           451: normal to overcommit vcpus; a 4-core machine machine might well provide 4
        !           452: vcpus to each domU.  One might also configure fewer vcpus for a domU.
1.48      gdt       453: 
                    454: A domain is provided with memory; this is controlled in the config
                    455: file by "memory = N" (in megabytes).  In the straightforward case, the
                    456: sum of the the memory allocated to the dom0 and all domUs must be less
1.33      gdt       457: than the available memory.
                    458: 
1.197     gdt       459: ## Balloon driver
                    460: 
                    461: Xen provides a `balloon` driver, which can be used to let domains use
                    462: more memory temporarily.
                    463: 
                    464: \todo Explain how to set up a aystem to use the balloon scheme in a
                    465: useful manner.
1.28      gdt       466: 
1.181     gdt       467: ## Virtual disks
1.28      gdt       468: 
1.158     maxv      469: In domU config files, the disks are defined as a sequence of 3-tuples:
                    470: 
                    471:  * The first element is "method:/path/to/disk". Common methods are
1.162     gutterid  472:    "file:" for a file-backed vnd, and "phy:" for something that is already
                    473:    a device, such as an LVM logical volume.
1.158     maxv      474: 
                    475:  * The second element is an artifact of how virtual disks are passed to
                    476:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
                    477:    are given a device name to associate with the disk, and values like
                    478:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
                    479:    as xbd0, the second as xbd1, and so on.  However, xl demands a
                    480:    second argument.  The name given is converted to a major/minor by
                    481:    calling stat(2) on the name in /dev and this is passed to the domU.
                    482:    In the general case, the dom0 and domU can be different operating
                    483:    systems, and it is an unwarranted assumption that they have consistent
                    484:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
                    485:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
                    486:    for the second works fine and avoids this issue.  For a GNU/Linux
                    487:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
                    488:    /dev/hda1.
1.48      gdt       489: 
1.158     maxv      490:  * The third element is "w" for writable disks, and "r" for read-only
                    491:    disks.
                    492: 
                    493: Example:
                    494: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
                    495: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
                    496: """]]
1.28      gdt       497: 
1.127     gdt       498: Note that NetBSD by default creates only vnd[0123].  If you need more
                    499: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
                    500: dom0.
                    501: 
1.187     gdt       502: ## Virtual Networking
1.28      gdt       503: 
1.111     wiz       504: Xen provides virtual Ethernets, each of which connects the dom0 and a
1.46      gdt       505: domU.  For each virtual network, there is an interface "xvifN.M" in
1.158     maxv      506: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
                    507: The interfaces behave as if there is an Ethernet with two
1.111     wiz       508: adapters connected.  From this primitive, one can construct various
1.46      gdt       509: configurations.  We focus on two common and useful cases for which
                    510: there are existing scripts: bridging and NAT.
1.28      gdt       511: 
1.48      gdt       512: With bridging (in the example above), the domU perceives itself to be
                    513: on the same network as the dom0.  For server virtualization, this is
                    514: usually best.  Bridging is accomplished by creating a bridge(4) device
                    515: and adding the dom0's physical interface and the various xvifN.0
                    516: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
                    517: config file.  The bridge must be set up already in the dom0; an
                    518: example /etc/ifconfig.bridge0 is:
1.46      gdt       519: 
1.157     maxv      520: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
                    521: create
                    522: up
                    523: !brconfig bridge0 add wm0
                    524: """]]
1.28      gdt       525: 
                    526: With NAT, the domU perceives itself to be behind a NAT running on the
                    527: dom0.  This is often appropriate when running Xen on a workstation.
1.48      gdt       528: TODO: NAT appears to be configured by "vif = [ '' ]".
1.28      gdt       529: 
1.49      gdt       530: The MAC address specified is the one used for the interface in the new
1.53      gdt       531: domain.  The interface in dom0 will use this address XOR'd with
1.49      gdt       532: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
                    533: 
1.187     gdt       534: ## Starting domains automatically
1.28      gdt       535: 
1.158     maxv      536: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
                    537: down cleanly on dom0 shutdown, add the following in rc.conf:
1.28      gdt       538: 
1.158     maxv      539: [[!template id=filecontent name="/etc/rc.conf" text="""
                    540: xendomains="domU-netbsd domU-linux"
                    541: """]]
1.28      gdt       542: 
1.188     gdt       543: # domU setup for specific systems
1.14      gdt       544: 
                    545: Creating domUs is almost entirely independent of operating system.  We
1.188     gdt       546: have already presented the basics of config files in the previous system.
                    547: 
                    548: Of course, this section presumes that you have a working dom0.
1.14      gdt       549: 
1.187     gdt       550: ## Creating a NetBSD PV domU
                    551: 
1.49      gdt       552: See the earlier config file, and adjust memory.  Decide on how much
1.162     gutterid  553: storage you will provide, and prepare it (file or LVM).
1.49      gdt       554: 
1.111     wiz       555: While the kernel will be obtained from the dom0 file system, the same
1.49      gdt       556: file should be present in the domU as /netbsd so that tools like
                    557: savecore(8) can work.   (This is helpful but not necessary.)
                    558: 
1.188     gdt       559: The kernel must be specifically built for Xen, to use PV interfacesas
                    560: a domU.  NetBSD release builds provide the following kernels:
1.49      gdt       561: 
                    562:         i386 XEN3PAE_DOMU
1.95      gdt       563:         amd64 XEN3_DOMU
1.5       mspo      564: 
1.49      gdt       565: This will boot NetBSD, but this is not that useful if the disk is
1.188     gdt       566: empty.  One approach is to unpack sets onto the disk outside of Xen
1.49      gdt       567: (by mounting it, just as you would prepare a physical disk for a
                    568: system you can't run the installer on).
                    569: 
                    570: A second approach is to run an INSTALL kernel, which has a miniroot
                    571: and can load sets from the network.  To do this, copy the INSTALL
                    572: kernel to / and change the kernel line in the config file to:
1.5       mspo      573: 
1.49      gdt       574:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
1.5       mspo      575: 
1.163     gson      576: Then, start the domain as "xl create -c configfile".
1.1       mspo      577: 
1.49      gdt       578: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
                    579: line should be used in the config file.
1.1       mspo      580: 
1.3       mspo      581:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
1.1       mspo      582: 
                    583: After booting the domain, the option to install via CDROM may be
1.49      gdt       584: selected.  The CDROM device should be changed to `xbd1d`.
1.1       mspo      585: 
1.188     gdt       586: Once done installing, "halt -p" the new domain (don't reboot or halt:
1.49      gdt       587: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
                    588: config file), switch the config file back to the XEN3_DOMU kernel,
                    589: and start the new domain again. Now it should be able to use "root on
1.188     gdt       590: xbd0a" and you should have a functional NetBSD domU.
1.1       mspo      591: 
1.49      gdt       592: TODO: check if this is still accurate.
1.1       mspo      593: When the new domain is booting you'll see some warnings about *wscons*
                    594: and the pseudo-terminals. These can be fixed by editing the files
1.5       mspo      595: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
                    596: `/etc/ttys`, except *console*, like this:
1.1       mspo      597: 
1.3       mspo      598:     console "/usr/libexec/getty Pc"         vt100   on secure
                    599:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
                    600:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
                    601:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
                    602:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
1.1       mspo      603: 
1.5       mspo      604: Finally, all screens must be commented out from `/etc/wscons.conf`.
1.1       mspo      605: 
1.192     gdt       606: One should also run `powerd` in a domU, but this should not need
                    607: configuring.  With powerd, the domain will run a controlled shutdown
                    608: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
                    609: receiving a synthetic `power button pressed` signal.  In 9 and
                    610: current, `powerd` is run by default under Xen kernels (or if ACPI is
                    611: present), and it can be added to rc.conf if not.
1.1       mspo      612: 
1.92      gdt       613: It is not strictly necessary to have a kernel (as /netbsd) in the domU
1.111     wiz       614: file system.  However, various programs (e.g. netstat) will use that
1.92      gdt       615: kernel to look up symbols to read from kernel virtual memory.  If
                    616: /netbsd is not the running kernel, those lookups will fail.  (This is
                    617: not really a Xen-specific issue, but because the domU kernel is
                    618: obtained from the dom0, it is far more likely to be out of sync or
                    619: missing with Xen.)
                    620: 
1.187     gdt       621: Note that NetBSD by default creates only xbd[0123].  If you need more
                    622: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
                    623: 
1.196     gdt       624: ## Creating a Linux PV domU
1.1       mspo      625: 
                    626: Creating unprivileged Linux domains isn't much different from
                    627: unprivileged NetBSD domains, but there are some details to know.
                    628: 
                    629: First, the second parameter passed to the disk declaration (the '0x1' in
                    630: the example below)
                    631: 
1.3       mspo      632:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
1.1       mspo      633: 
                    634: does matter to Linux. It wants a Linux device number here (e.g. 0x300
1.49      gdt       635: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
                    636: So, hda1 which has major 3 and minor 1 on a Linux system will have
                    637: device number 0x301.  Alternatively, devices names can be used (hda,
                    638: hdb, ...)  as xentools has a table to map these names to devices
                    639: numbers.  To export a partition to a Linux guest we can use:
1.1       mspo      640: 
1.49      gdt       641:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
                    642:         root = "/dev/hda1 ro"
1.1       mspo      643: 
                    644: and it will appear as /dev/hda on the Linux system, and be used as root
                    645: partition.
                    646: 
1.49      gdt       647: To install the Linux system on the partition to be exported to the
                    648: guest domain, the following method can be used: install
                    649: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
                    650: that will be the root partition of your Linux domain, and mount it.
                    651: Then copy the files from a working Linux system, make adjustments in
                    652: `/etc` (fstab, network config).  It should also be possible to extract
                    653: binary packages such as .rpm or .deb directly to the mounted partition
                    654: using the appropriate tool, possibly running under NetBSD's Linux
1.111     wiz       655: emulation.  Once the file system has been populated, umount it.  If
                    656: desirable, the file system can be converted to ext3 using tune2fs -j.
1.49      gdt       657: It should now be possible to boot the Linux guest domain, using one of
                    658: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
1.1       mspo      659: 
1.111     wiz       660: To get the Linux console right, you need to add:
1.1       mspo      661: 
1.3       mspo      662:     extra = "xencons=tty1"
1.1       mspo      663: 
1.111     wiz       664: to your configuration since not all Linux distributions auto-attach a
1.1       mspo      665: tty to the xen console.
                    666: 
1.180     gdt       667: ## Creating a NetBSD HVM domU
                    668: 
1.196     gdt       669: Use type='hvm', probably.  Use a GENERIC kernel within the disk image.
1.180     gdt       670: 
                    671: ## Creating a NetBSD PVH domU
                    672: 
1.196     gdt       673: This only works with a current kernel in the domU.
1.180     gdt       674: 
1.196     gdt       675: Use type='pvh'.  Probably, use a GENERIC kernel within the disk image,
                    676: which in current has PV support.
                    677: 
                    678: \todo Verify.
                    679: 
                    680: \todo Verify if one can have current PVH domU on a 9 dom0.
1.180     gdt       681: 
1.187     gdt       682: ## Creating a Solaris domU
1.1       mspo      683: 
1.50      gdt       684: See possibly outdated
                    685: [Solaris domU instructions](/ports/xen/howto-solaris/).
1.5       mspo      686: 
1.187     gdt       687: ## PCI passthrough: Using PCI devices in guest domains
1.1       mspo      688: 
1.180     gdt       689: NB: PCI passthrough only works on some Xen versions and as of 2020 it
1.196     gdt       690: is not clear that it works on any version in pkgsrc.  \todo Reports
1.180     gdt       691: confirming or denying this notion should be sent to port-xen@.
                    692: 
1.53      gdt       693: The dom0 can give other domains access to selected PCI
1.52      gdt       694: devices. This can allow, for example, a non-privileged domain to have
                    695: access to a physical network interface or disk controller.  However,
                    696: keep in mind that giving a domain access to a PCI device most likely
                    697: will give the domain read/write access to the whole physical memory,
                    698: as PCs don't have an IOMMU to restrict memory access to DMA-capable
1.53      gdt       699: device.  Also, it's not possible to export ISA devices to non-dom0
1.52      gdt       700: domains, which means that the primary VGA adapter can't be exported.
                    701: A guest domain trying to access the VGA registers will panic.
                    702: 
1.53      gdt       703: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
1.52      gdt       704: not been ported to later versions at this time.
                    705: 
                    706: For a PCI device to be exported to a domU, is has to be attached to
                    707: the "pciback" driver in dom0.  Devices passed to the dom0 via the
                    708: pciback.hide boot parameter will attach to "pciback" instead of the
                    709: usual driver.  The list of devices is specified as "(bus:dev.func)",
1.5       mspo      710: where bus and dev are 2-digit hexadecimal numbers, and func a
                    711: single-digit number:
1.1       mspo      712: 
1.52      gdt       713:         pciback.hide=(00:0a.0)(00:06.0)
1.1       mspo      714: 
1.52      gdt       715: pciback devices should show up in the dom0's boot messages, and the
1.5       mspo      716: devices should be listed in the `/kern/xen/pci` directory.
1.1       mspo      717: 
1.52      gdt       718: PCI devices to be exported to a domU are listed in the "pci" array of
                    719: the domU's config file, with the format "0000:bus:dev.func".
1.1       mspo      720: 
1.52      gdt       721:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
1.1       mspo      722: 
1.52      gdt       723: In the domU an "xpci" device will show up, to which one or more pci
1.111     wiz       724: buses will attach.  Then the PCI drivers will attach to PCI buses as
1.52      gdt       725: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
                    726: or any PCI drivers built in by default; you have to build your own
                    727: kernel to use PCI devices in a domU.  Here's a kernel config example;
                    728: note that only the "xpci" lines are unusual.
                    729: 
                    730:         include         "arch/i386/conf/XEN3_DOMU"
                    731: 
1.111     wiz       732:         # Add support for PCI buses to the XEN3_DOMU kernel
1.52      gdt       733:         xpci* at xenbus ?
                    734:         pci* at xpci ?
                    735: 
                    736:         # PCI USB controllers
                    737:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
                    738: 
                    739:         # USB bus support
                    740:         usb*    at uhci?
                    741: 
                    742:         # USB Hubs
                    743:         uhub*   at usb?
                    744:         uhub*   at uhub? port ? configuration ? interface ?
                    745: 
                    746:         # USB Mass Storage
                    747:         umass*  at uhub? port ? configuration ? interface ?
                    748:         wd*     at umass?
                    749:         # SCSI controllers
                    750:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
                    751: 
                    752:         # SCSI bus support (for both ahc and umass)
                    753:         scsibus* at scsi?
                    754: 
                    755:         # SCSI devices
                    756:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
                    757:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
1.1       mspo      758: 
                    759: 
1.189     gdt       760: # Miscellaneous Information
1.173     gdt       761: 
1.189     gdt       762: ## Nesting under Linux KVM
                    763: 
1.205   ! gdt       764: It is possible to run Xen and a NetBSD dom0 under Linux KVM.  One
1.189     gdt       765: can enable virtio in the dom0 for greater speed.
                    766: 
1.205   ! gdt       767: ## Nesting under qemu
        !           768: 
        !           769: It is possible to run Xen and a NetBSD dom0 under qemu on NetBSD, and
        !           770: also with nvmm.
        !           771: \todo Check this.
        !           772: 
1.189     gdt       773: ## Other nesting
                    774: 
                    775: In theory, any full emulation should be able to run Xen and a NetBSD
                    776: dom0.  The HOWTO does not currently have information about Xen XVM
1.205   ! gdt       777: mode, Virtualbox, etc.
1.189     gdt       778: 
                    779: ## NetBSD 5 as domU
1.173     gdt       780: 
1.176     gdt       781: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
1.175     gdt       782: (However, NetBSD 5 systems should be updated to a supported version.)
1.173     gdt       783: 
                    784: # NetBSD as a domU in a VPS
1.28      gdt       785: 
                    786: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
                    787: hardware.  This section explains how to deal with Xen in a domU as a
                    788: virtual private server where you do not control or have access to the
1.70      gdt       789: dom0.  This is not intended to be an exhaustive list of VPS providers;
                    790: only a few are mentioned that specifically support NetBSD.
1.28      gdt       791: 
1.52      gdt       792: VPS operators provide varying degrees of access and mechanisms for
                    793: configuration.  The big issue is usually how one controls which kernel
1.111     wiz       794: is booted, because the kernel is nominally in the dom0 file system (to
                    795: which VPS users do not normally have access).  A second issue is how
1.70      gdt       796: to install NetBSD.
1.52      gdt       797: A VPS user may want to compile a kernel for security updates, to run
                    798: npf, run IPsec, or any other reason why someone would want to change
                    799: their kernel.
                    800: 
1.111     wiz       801: One approach is to have an administrative interface to upload a kernel,
1.68      gdt       802: or to select from a prepopulated list.  Other approaches are pygrub
1.59      gdt       803: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
1.111     wiz       804: kernel from the domU file system.  This is closer to a regular physical
1.59      gdt       805: computer, where someone who controls a machine can replace the kernel.
1.52      gdt       806: 
1.74      gdt       807: A second issue is multiple CPUs.  With NetBSD 6, domUs support
                    808: multiple vcpus, and it is typical for VPS providers to enable multiple
                    809: CPUs for NetBSD domUs.
                    810: 
1.180     gdt       811: ## Complexities due to Xen changes
                    812: 
                    813: Xen has many security advisories and people running Xen systems make
                    814: different choices.
                    815: 
                    816: ### stub domains
                    817: 
1.205   ! gdt       818: Some (Linux) dom0 systems use something called "stub domains" to
1.180     gdt       819: isolate qemu from the dom0 system, as a security and reliabilty
                    820: mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
                    821: ends up using PIO for disks rather than DMA.  Of course, all of this
                    822: is emulated, but emulated PIO is unusably slow.  This problem is not
                    823: currently understood.
                    824: 
                    825: ### Grant tables
                    826: 
                    827: There are multiple versions of using grant tables, and some security
1.205   ! gdt       828: advisories have suggested disabling some versions.  NetBSD through 9
        !           829: uses version 1 and NetBSD-current uses version 2.  This can lead to
1.180     gdt       830: "NetBSD current doesn't run on hosting provider X" situations.
                    831: 
                    832: \todo Explain better.
                    833: 
1.181     gdt       834: ## Boot methods
                    835: 
                    836: ### pvgrub
1.59      gdt       837: 
                    838: pvgrub is a version of grub that uses PV operations instead of BIOS
                    839: calls.  It is booted from the dom0 as the domU kernel, and then reads
1.111     wiz       840: /grub/menu.lst and loads a kernel from the domU file system.
1.59      gdt       841: 
1.70      gdt       842: It appears that [grub's FFS
                    843: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
                    844: does not support all aspects of modern FFS, but there are also reports
1.205   ! gdt       845: that FFSv2 works fine.
1.59      gdt       846: 
1.181     gdt       847: ### pygrub
1.168     wiki      848: 
1.205   ! gdt       849: As of 2014, pygrub seems to be of mostly historical interest.  As of
        !           850: 2021, the section should perhaps be outright deleted.
        !           851: 
1.168     wiki      852: pygrub runs in the dom0 and looks into the domU file system.  This
                    853: implies that the domU must have a kernel in a file system in a format
                    854: known to pygrub.
                    855: 
                    856: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
1.205   ! gdt       857: and is inherently less secure than pvgrub due to running inside
        !           858: dom0. For both these reasons, pygrub should not be used, and is only
        !           859: still present so that historical DomU images using it still work.
        !           860: 
        !           861: ## Specific Providers
        !           862: 
        !           863: The intent is to list providers only if they document support for
        !           864: running NetBSD, and to point to their resources briefly.
1.168     wiki      865: 
1.205   ! gdt       866: ### panix.com
1.168     wiki      867: 
1.205   ! gdt       868: [Panix](http://www.panix.com/) provides NetBSD as an OS option.  See
        !           869: https://www.panix.com/v-colo/nupgrade.html for some information.
        !           870: Users can use pvgrub.  Panix reports that pvgrub works with FFsv2 with
        !           871: 16K/2K and 32K/4K block/frag sizes (and hence with defaults from
        !           872: "newfs -O 2").  See [Panix's pvgrub
        !           873: page](http://www.panix.com/v-colo/grub.html) which describes how to
        !           874: boot NetBSD.
        !           875: 
        !           876: ### prgmr.com
        !           877: 
        !           878: [prgmr.com](http://prgmr.com/) provides released versions of
        !           879: NetBSD/amd64 as installation options.  Users can use pvgrub to boot
        !           880: their own kernel, and a small FAT32 /boot is encouraged.  See the
        !           881: [prgmr.com NetBSD
        !           882: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
        !           883: (which is in need of updating).
1.181     gdt       884: 
                    885: ### Amazon
1.59      gdt       886: 
1.143     wiki      887: See the [Amazon EC2 page](/amazon_ec2/).

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