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version 1.175, 2020/11/13 19:43:26 version 1.185, 2020/11/15 14:59:54
Line 8  systems which operate in an unprivileged Line 8  systems which operate in an unprivileged
 from the domU systems are forwarded by the Xen hypervisor to the dom0 to be  from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
 fulfilled.  fulfilled.
   
 Xen supports different styles of guests; see [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM) and [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2)_Domu) for upstream documentation.  This HOWTO presumes a basic familiarity with the Xen system
   architecture, with installing NetBSD on amd64 hardware, and with
   installing software from pkgsrc.  See also the [Xen
   website](http://www.xenproject.org/).
   
   [[!toc]]
   
   # Overview
   
   The basic concept of Xen is that the hypervisor (xenkernel) runs on
   the hardware, and runs a privileged domain ("dom0") that can access
   disks/networking/etc.  One then runs additonal unprivileged domains
   (each a "domU"), presumably to do something useful.
   
   This HOWTO addresses how to run a NetBSD dom0 (and hence also build
   xen itself).  It also addresses how to run domUs in that environment,
   and how to deal with having a domU in a Xen environment run by someone
   else and/or not running NetBSD.
   
   ## Guest Styles
   
   Xen supports different styles of guests.
   
 [[!table data="""  [[!table data="""
 Style of guest  |Supported by NetBSD  Style of guest  |Supported by NetBSD
 PV              |Yes (dom0, domU)  PV              |Yes (dom0, domU)
 HVM             |Yes (domU)  HVM             |Yes (domU)
 PVH             |current-only (domU, dom0 not yet)  
 PVHVM           |current-only (domU)  PVHVM           |current-only (domU)
   PVH             |current-only (domU, dom0 not yet)
 """]]  """]]
   
 In Para-Virtualized (PV) mode, the guest OS does not attempt to access  In Para-Virtualized (PV) mode, the guest OS does not attempt to access
 hardware directly, but instead makes hypercalls to the hypervisor; PV  hardware directly, but instead makes hypercalls to the hypervisor; PV
 guests must be specifically coded for Xen.  guests must be specifically coded for Xen.
   See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
   
 In HVM mode, no guest modification is required; however, hardware  In HVM mode, no guest modification is required; however, hardware
 support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.  support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
   The dom0 runs qemu to emulate hardware.
   
 In PVH mode, the guest uses PV interfaces for IO and native interfaces for everything else.  In PVHVM mode, the guest runs as HVM, but additionally can use PV
   drivers for efficiency.
 In PVHVM mode, the guest mostly runs as HVM, but can use PV drivers for efficiency.  See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
   
   There have been two PVH modes: original PVH and PVHv2.  Original PVH
   was based on PV mode and is no longer relevant at all.  PVHv2 is
   basically lightweight HVM with PV drivers.  A critical feature of it
   is that qemu is not needed; the hypervisor can do the emulation that
   is required.  Thus, a dom0 can be PVHv2.
   The source code uses PVH and config files use pvh; this refers to PVHv2.
   See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
   
 \todo Explain about "HVM with PV drivers".  At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   
 At boot, the dom0 kernel is loaded as a module with Xen as the kernel.  
 The dom0 can start one or more domUs.  (Booting is explained in detail  The dom0 can start one or more domUs.  (Booting is explained in detail
 in the dom0 section.)  in the dom0 section.)
   
 This HOWTO presumes a basic familiarity with the Xen system  ## CPU Architecture
 architecture, with installing NetBSD on i386/amd64 hardware, and with  
 installing software from pkgsrc.  See also the [Xen  
 website](http://www.xenproject.org/).  
   
 [[!toc]]  Xen runs on x86_64 hardware (the NetBSD amd64 port).
   
   There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   
   The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   
 # Versions and Support  The domU can be i386PAE or amd64.
   i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
   
   ## Xen Versions
   
 In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages  In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
 xenkernel and xentools.  We will refer only to the kernel versions,  xenkernel and xentools.  We will refer only to the kernel versions,
Line 52  matching versions. Line 85  matching versions.
 Versions available in pkgsrc:  Versions available in pkgsrc:
   
 [[!table data="""  [[!table data="""
 Xen Version     |Package Name   |Xen CPU Support        |xm?    |EOL'ed By Upstream  Xen Version     |Package Name   |Xen CPU Support        |EOL'ed By Upstream
 4.2             |xenkernel42    |i386 x86_64            |yes    |Yes  4.11            |xenkernel411   |x86_64                 |No
 4.5             |xenkernel45    |x86_64                 |       |Yes  4.13            |xenkernel413   |x86_64                 |No
 4.6             |xenkernel46    |x86_64                 |       |Yes  
 4.8             |xenkernel48    |x86_64                 |       |Yes  
 4.11            |xenkernel411   |x86_64                 |       |No  
 """]]  """]]
   
 See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).  See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
   
 Multiprocessor (SMP) support in NetBSD differs depending on the domain:  
   
 [[!table data="""  
 Domain          |Supports SMP  
 dom0            |No  
 domU            |Yes  
 """]]  
   
 Note: NetBSD support is called XEN3.  However, it does support Xen 4,  
 because the hypercall interface has remained identical.  
   
 Older Xen had a python-based management tool called xm, now replaced  Older Xen had a python-based management tool called xm, now replaced
 by xl.  xm is obsolete, but 4.2 remains in pkgsrc because migrating  by xl.
 from xm to xl is not always trivial, and because 4.2 is the last  
 version to run on an i386 dom0.  
   
 Architecture  ## NetBSD versions
 ------------  
   
 Xen 4.5 and later runs on x86_64 hardware (the NetBSD amd64 port).  Xen has been supported in NetBSD for a long time, at least since 2005.
 Xen 4.2 can in theory use i386 hardware, but we do not have  Initially Xen was PV only.
 recent reports of success.  
   
 The dom0 system, plus each domU, can be either i386PAE or amd64.  NetBSD 8 and up support PV and HVM modes.
 i386 without PAE is not supported.  
   
 The standard approach is to use NetBSD/amd64 for the dom0.  Support for PVHVM and PVH is available only in NetBSD-current.
   
 To use an i386PAE dom0 (other than on 4.2), one must build or obtain a  NetBSD as a dom0 does not run SMP, because some drivers are not yet
 64bit Xen kernel and install it on the system.  safe for this.  \todo Link to more information about what needs work.
   
 For domUs, i386PAE is considered as  NetBSD, when run as a domU, can and does typically run SMP.
 [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html)  
 than amd64.  Note: NetBSD support is called XEN3.  However, it does support Xen 4,
   because the hypercall interface has remained identical.
   
 # Creating a dom0  # Creating a dom0
   
Line 107  In 2018-05, trouble booting a dom0 was r Line 122  In 2018-05, trouble booting a dom0 was r
 512M it worked reliably.  This does not make sense, but if you see  512M it worked reliably.  This does not make sense, but if you see
 "not ELF" after Xen boots, try increasing dom0 RAM.  "not ELF" after Xen boots, try increasing dom0 RAM.
   
 Installation of NetBSD  ## Installation of NetBSD
 ----------------------  
   
 [Install NetBSD/amd64](/guide/inst/)  [Install NetBSD/amd64](/guide/inst/)
 just as you would if you were not using Xen.  just as you would if you were not using Xen.
   
 Installation of Xen  ## Installation of Xen
 -------------------  
   
 We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as  We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
 dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.  dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
   
 Once this is done, install the Xen kernel itself:  Once this is done, install the Xen kernel itself:
Line 156  itself uses (in this case, the serial po Line 169  itself uses (in this case, the serial po
 In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,  In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
 to force only one vcpu to be provided (since NetBSD dom0 can't use  to force only one vcpu to be provided (since NetBSD dom0 can't use
 more) and to pin that vcpu to a physical CPU. Xen has  more) and to pin that vcpu to a physical CPU. Xen has
 [many boot options](http://xenbits.xenproject.org/docs/4.8-testing/misc/xen-command-line.html),  [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
 and other than dom0 memory and max_vcpus, they are generally not  and other than dom0 memory and max_vcpus, they are generally not
 necessary.  necessary.
   
Line 204  make this work, one should not expect to Line 217  make this work, one should not expect to
 (and thus xencommons).  There is currently no reason to expect that  (and thus xencommons).  There is currently no reason to expect that
 this will get fixed any time soon.  this will get fixed any time soon.
   
 anita (for testing NetBSD)  ## anita (for testing NetBSD)
 --------------------------  
   
 With the setup so far (assuming 4.8/xl), one should be able to run  With the setup so far, one should be able to run
 anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as  anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
 root, because anita must create a domU):  root, because anita must create a domU):
   
Line 215  root, because anita must create a domU): Line 227  root, because anita must create a domU):
 anita --vmm=xl test file:///usr/obj/i386/  anita --vmm=xl test file:///usr/obj/i386/
 """]]  """]]
   
 Xen-specific NetBSD issues  ## Xen-specific NetBSD issues
 --------------------------  
   
 There are (at least) two additional things different about NetBSD as a  There are (at least) two additional things different about NetBSD as a
 dom0 kernel compared to hardware.  dom0 kernel compared to hardware.
Line 230  options as GENERIC.  While it is debatab Line 241  options as GENERIC.  While it is debatab
 bug, users should be aware of this and can simply add missing config  bug, users should be aware of this and can simply add missing config
 items if desired.  items if desired.
   
 Updating NetBSD in a dom0  ## Updating NetBSD in a dom0
 -------------------------  
   
 This is just like updating NetBSD on bare hardware, assuming the new  This is just like updating NetBSD on bare hardware, assuming the new
 version supports the version of Xen you are running.  Generally, one  version supports the version of Xen you are running.  Generally, one
Line 241  and adjusts `/etc`. Line 251  and adjusts `/etc`.
 Note that one must update both the non-Xen kernel typically used for  Note that one must update both the non-Xen kernel typically used for
 rescue purposes and the DOM0 kernel used with Xen.  rescue purposes and the DOM0 kernel used with Xen.
   
 Converting from grub to /boot  ## Converting from grub to /boot
 -----------------------------  
   
 These instructions were used to convert a system from  These instructions were used to convert a system from
 grub to /boot.  The system was originally installed in February of  grub to /boot.  The system was originally installed in February of
Line 272  default=1 Line 281  default=1
 timeout=30  timeout=30
 """]]  """]]
   
 Upgrading Xen versions  ## Upgrading Xen versions
 ---------------------  
   
 Minor version upgrades are trivial.  Just rebuild/replace the  Minor version upgrades are trivial.  Just rebuild/replace the
 xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`  xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
Line 294  mediated by Xen, and configured in the d Line 302  mediated by Xen, and configured in the d
 Entropy in domUs can be an issue; physical disks and network are on  Entropy in domUs can be an issue; physical disks and network are on
 the dom0.  NetBSD's /dev/random system works, but is often challenged.  the dom0.  NetBSD's /dev/random system works, but is often challenged.
   
 Config files  ## Config files
 ------------  
   
 See /usr/pkg/share/examples/xen/xlexample*  See /usr/pkg/share/examples/xen/xlexample*
 for a small number of well-commented examples, mostly for running  for a small number of well-commented examples, mostly for running
Line 341  equivalent to pushing the power button;  Line 348  equivalent to pushing the power button; 
 power-press event and do a clean shutdown.  Shutting down the dom0  power-press event and do a clean shutdown.  Shutting down the dom0
 will trigger controlled shutdowns of all configured domUs.  will trigger controlled shutdowns of all configured domUs.
   
 CPU and memory  ## CPU and memory
 --------------  
   
 A domain is provided with some number of vcpus, up to the number  A domain is provided with some number of vcpus, up to the number
 of CPUs seen by the hypervisor. For a domU, it is controlled  of CPUs seen by the hypervisor. For a domU, it is controlled
Line 356  than the available memory. Line 362  than the available memory.
 Xen also provides a "balloon" driver, which can be used to let domains  Xen also provides a "balloon" driver, which can be used to let domains
 use more memory temporarily.  use more memory temporarily.
   
 Virtual disks  ## Virtual disks
 -------------  
   
 In domU config files, the disks are defined as a sequence of 3-tuples:  In domU config files, the disks are defined as a sequence of 3-tuples:
   
Line 438  down cleanly on dom0 shutdown, add the f Line 443  down cleanly on dom0 shutdown, add the f
 xendomains="domU-netbsd domU-linux"  xendomains="domU-netbsd domU-linux"
 """]]  """]]
   
 #Creating a domU  # Creating a domU
   
 Creating domUs is almost entirely independent of operating system.  We  Creating domUs is almost entirely independent of operating system.  We
 have already presented the basics of config files.  Note that you must  have already presented the basics of config files.  Note that you must
 have already completed the dom0 setup so that "xl list" works.  have already completed the dom0 setup so that "xl list" works.
   
 Creating a NetBSD domU  Creating a NetBSD PV domU
 ----------------------  --------------------------
   
 See the earlier config file, and adjust memory.  Decide on how much  See the earlier config file, and adjust memory.  Decide on how much
 storage you will provide, and prepare it (file or LVM).  storage you will provide, and prepare it (file or LVM).
Line 506  It is also desirable to add Line 511  It is also desirable to add
         powerd=YES          powerd=YES
   
 in rc.conf. This way, the domain will be properly shut down if  in rc.conf. This way, the domain will be properly shut down if
 `xm shutdown -R` or `xm shutdown -H` is used on the dom0.  `xl shutdown -R` or `xl shutdown -H` is used on the dom0.
   \todo Check the translation to xl.
   
 It is not strictly necessary to have a kernel (as /netbsd) in the domU  It is not strictly necessary to have a kernel (as /netbsd) in the domU
 file system.  However, various programs (e.g. netstat) will use that  file system.  However, various programs (e.g. netstat) will use that
Line 560  To get the Linux console right, you need Line 566  To get the Linux console right, you need
 to your configuration since not all Linux distributions auto-attach a  to your configuration since not all Linux distributions auto-attach a
 tty to the xen console.  tty to the xen console.
   
   ## Creating a NetBSD HVM domU
   
   Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
   
   ## Creating a NetBSD PVH domU
   
   Use type='pvh'.
   
   \todo Explain where the kernel comes from.
   
   
 Creating a Solaris domU  Creating a Solaris domU
 -----------------------  -----------------------
   
Line 570  See possibly outdated Line 587  See possibly outdated
 PCI passthrough: Using PCI devices in guest domains  PCI passthrough: Using PCI devices in guest domains
 ---------------------------------------------------  ---------------------------------------------------
   
   NB: PCI passthrough only works on some Xen versions and as of 2020 it
   is not clear that it works on any version in pkgsrc.  Reports
   confirming or denying this notion should be sent to port-xen@.
   
 The dom0 can give other domains access to selected PCI  The dom0 can give other domains access to selected PCI
 devices. This can allow, for example, a non-privileged domain to have  devices. This can allow, for example, a non-privileged domain to have
 access to a physical network interface or disk controller.  However,  access to a physical network interface or disk controller.  However,
Line 641  note that only the "xpci" lines are unus Line 662  note that only the "xpci" lines are unus
   
 ## domU  ## domU
   
 [NetBSD 5 is known to panic.]  [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
 (http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)  
 (However, NetBSD 5 systems should be updated to a supported version.)  (However, NetBSD 5 systems should be updated to a supported version.)
   
 # NetBSD as a domU in a VPS  # NetBSD as a domU in a VPS
Line 672  A second issue is multiple CPUs.  With N Line 692  A second issue is multiple CPUs.  With N
 multiple vcpus, and it is typical for VPS providers to enable multiple  multiple vcpus, and it is typical for VPS providers to enable multiple
 CPUs for NetBSD domUs.  CPUs for NetBSD domUs.
   
 pvgrub  ## Complexities due to Xen changes
 ------  
   Xen has many security advisories and people running Xen systems make
   different choices.
   
   ### stub domains
   
   Some (Linux only?) dom0 systems use something called "stub domains" to
   isolate qemu from the dom0 system, as a security and reliabilty
   mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
   ends up using PIO for disks rather than DMA.  Of course, all of this
   is emulated, but emulated PIO is unusably slow.  This problem is not
   currently understood.
   
   ### Grant tables
   
   There are multiple versions of using grant tables, and some security
   advisories have suggested disabling some versions.  Some versions of
   NetBSD apparently only use specific versions and this can lead to
   "NetBSD current doesn't run on hosting provider X" situations.
   
   \todo Explain better.
   
   ## Boot methods
   
   ### pvgrub
   
 pvgrub is a version of grub that uses PV operations instead of BIOS  pvgrub is a version of grub that uses PV operations instead of BIOS
 calls.  It is booted from the dom0 as the domU kernel, and then reads  calls.  It is booted from the dom0 as the domU kernel, and then reads
Line 698  partition for the kernel with the intent Line 742  partition for the kernel with the intent
 which leads to /netbsd not being the actual kernel.  One must remember  which leads to /netbsd not being the actual kernel.  One must remember
 to update the special boot partition.  to update the special boot partition.
   
 pygrub  ### pygrub
 -------  
   
 pygrub runs in the dom0 and looks into the domU file system.  This  pygrub runs in the dom0 and looks into the domU file system.  This
 implies that the domU must have a kernel in a file system in a format  implies that the domU must have a kernel in a file system in a format
Line 713  historical DomU images using it still wo Line 756  historical DomU images using it still wo
 As of 2014, pygrub seems to be of mostly historical  As of 2014, pygrub seems to be of mostly historical
 interest. New DomUs should use pvgrub.  interest. New DomUs should use pvgrub.
   
 Amazon  ## Specific Providers
 ------  
   ### Amazon
   
 See the [Amazon EC2 page](/amazon_ec2/).  See the [Amazon EC2 page](/amazon_ec2/).
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