--- wikisrc/ports/xen/howto.mdwn 2020/11/15 14:31:58 1.180 +++ wikisrc/ports/xen/howto.mdwn 2021/03/03 15:03:13 1.195 @@ -8,7 +8,31 @@ systems which operate in an unprivileged from the domU systems are forwarded by the Xen hypervisor to the dom0 to be 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. + +There are many choices one can make; the HOWTO recommends the standard +approach and limits discussion of alternatives in many cases. + +## Guest Styles + +Xen supports different styles of guests. [[!table data=""" Style of guest |Supported by NetBSD @@ -21,6 +45,7 @@ PVH |current-only (domU, dom0 not yet) In Para-Virtualized (PV) mode, the guest OS does not attempt to access hardware directly, but instead makes hypercalls to the hypervisor; PV 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 support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs. @@ -28,27 +53,32 @@ The dom0 runs qemu to emulate hardware. In PVHVM mode, the guest runs as HVM, but additionally 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). -At boot, the dom0 kernel is loaded as a module with Xen as the kernel. +At system 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 in the dom0 section.) -This HOWTO presumes a basic familiarity with the Xen system -architecture, with installing NetBSD on i386/amd64 hardware, and with -installing software from pkgsrc. See also the [Xen -website](http://www.xenproject.org/). +## CPU Architecture -[[!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. -# Versions and Support +The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.) + +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 xenkernel and xentools. We will refer only to the kernel versions, @@ -58,93 +88,154 @@ matching versions. Versions available in pkgsrc: [[!table data=""" -Xen Version |Package Name |Xen CPU Support |xm? |EOL'ed By Upstream -4.11 |xenkernel411 |x86_64 | |No -4.13 |xenkernel413 |x86_64 | |No +Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream +4.11 |xenkernel411 |x86_64 |No +4.13 |xenkernel413 |x86_64 |No """]] See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/). -Multiprocessor (SMP) support in NetBSD differs depending on the domain: +Older Xen had a python-based management tool called xm, now replaced +by xl. -[[!table data=""" -Domain |Supports SMP -dom0 |No -domU |Yes -"""]] +## NetBSD versions -Note: NetBSD support is called XEN3. However, it does support Xen 4, -because the hypercall interface has remained identical. +Xen has been supported in NetBSD for a long time, at least since 2005. +Initially Xen was PV only. -Older Xen had a python-based management tool called xm, now replaced -by xl. +NetBSD 8 and up support PV and HVM modes. -Architecture ------------- +Support for PVHVM and PVH is available only in NetBSD-current. -Xen 4.5 and later 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. +NetBSD up to and including NetBSD 9 as a dom0 does not run SMP, +because some drivers are not yet safe for this. NetBSD-current +supports SMP in dom0. -The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.) +NetBSD, when run as a domU, can and does typically run SMP. -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. +Note that while Xen 4.13 is current, the kernel support is still +called XEN3, because the hypercall interface has not changed +significantly. -# Creating a dom0 +# Creating a NetBSD dom0 -In order to install a NetBSD as a dom0, one must first install a normal -NetBSD system, and then pivot the install to a dom0 install by changing -the kernel and boot configuration. +In order to install a NetBSD as a dom0, one first installs a normal +NetBSD system, and then pivot the install to a dom0 install by +changing the kernel and boot configuration. In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with 512M it worked reliably. This does not make sense, but if you see "not ELF" after Xen boots, try increasing dom0 RAM. -Installation of NetBSD ----------------------- +## Installation of NetBSD -[Install NetBSD/amd64](/guide/inst/) -just as you would if you were not using Xen. +[Install NetBSD/amd64](/guide/inst/) just as you would if you were not +using Xen. Therefore, use the most recent release, or a build from +the most recent stable branch. Alternatively, use -current, being +mindful of all the usual caveats of lower stability of current, and +likely a bit more so. -Installation of Xen -------------------- +## Installation of Xen -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. +### Building Xen -Once this is done, install the Xen kernel itself: +Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable. +Therefore, choose 4.13. +In the dom0, install xenkernel413 and xentools413 from pkgsrc. + +Once this is done, copy the Xen kernel from where pkgsrc puts it to +where the boot process will be able to find it: [[!template id=programlisting text=""" -# cp /usr/pkg/xen48-kernel/xen.gz / +# cp -p /usr/pkg/xen413-kernel/xen.gz / """]] -Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel -can either be compiled manually, or downloaded from the NetBSD FTP, for -example at: +Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such +kernel can either be taken from a local release build.sh run, compiled +manually, or downloaded from the NetBSD FTP, for example at: [[!template id=programlisting text=""" -ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz +ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz """]] -Add a line to /boot.cfg to boot Xen: +### Configuring booting + +Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen: [[!template id=filecontent name="/boot.cfg" text=""" menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M +menu=Xen single user:load /netbsd-XEN3_DOM0.gz console=pc -s;multiboot /xen.gz dom0_mem=512M """]] This specifies that the dom0 should have 512MB of ram, leaving the rest -to be allocated for domUs. To use a serial console, use: +to be allocated for domUs. +NB: This says add, not replace, so that you will be able to more +easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may +want to set it as default. It is highly likely that you will have +trouble at some point, and keeping an up-to-date GENERIC for use in +fixing problems is the standard prudent approach. + +\todo Explain why rndseed is not set with Xen as part of the dom0 +subconfiguration. + +Beware that userconf statements must be attached to the dom0 load, and +may not be at top-level, because then they would try to configure the +hypervisor, if there is a way to pass them via multiboot . It appears +that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very +early with a heap overflow. + +### Console selection + +See boot_console(8). Understand that you should start from a place of +having console setup correct for booting GENERIC before trying to +configure Xen. + +Generally for GENERIC, one sets the console in bootxx_ffsv1 or +equivalent, and this is passed on to /boot (where one typically does +not set the console). This configuration of bootxx_ffsv1 should also +be in place for Xen systems, to allow seeing messages from /boot and +use of a keyboard to select a line from the menu. And, one should +have a working boot path to GENERIC for rescue situations. + +With GENERIC, the boot options are passed on to /netbsd, but there is +currently no mechanism to pass these via multiboot to the hypervisor. +Thus, in addition to configuring the console in the boot blocks, one +must also configure it for Xen. + +By default, the hypervisor (Xen itself) will use some sort of vga +device as the console, much like GENERIC uses by default. The vga +console is relinquished at the conclusion of hypervisor boot, before +the dom0 is started. Xen when using a vga console does not process +console input. + +The hypervisor can be configured to use a serial port console, e.g. [[!template id=filecontent name="/boot.cfg" text=""" -menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1 +menu=Xen:losad /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1 """]] +This example uses the first serial port (Xen counts from 1; this is +what NetBSD would call com0), and sets speed and parity. (The dom0 is +then configured to use the same serial port in this example.) + +With the hypervisor configured for a serial console, it can get input, +and there is a notion of passing this input to the dom0. \todo +Explain why, if Xen has a serial console, the dom0 console is +typically also configured to open that same serial port, instead of +getting the passthrough input via the xen console. + +One also configures the console for the dom0. While one might expect +console=pc to be default, following behavior of GENERIC, a hasty read +of the code suggests there is no default and booting without a +selected console might lead to a panic. Also, there is merit in +explicit configuration. Therefore the standard approach is to place +console=pc as part of the load statement for the dom0 kernel, or +alternatively console=com0. + +The NetBSD dom0 kernel will attach xencons(4) (the man page does not +exist), but this is not used as a console. It is used to obtain the +messages from the hypervisor's console; run `xl dmesg` to see them. -which will use the first serial port for Xen (which counts starting -from 1, unlike NetBSD which counts starting from 0), forcing -speed/parity. Because the NetBSD command line lacks a -"console=pc" argument, it will use the default "xencons" console device, -which directs the console I/O through Xen to the same console device Xen -itself uses (in this case, the serial port). +### Tuning 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 @@ -152,24 +243,29 @@ more) and to pin that vcpu to a physical [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 necessary. +\todo Revisit this advice with current. +\todo Explain if anyone has ever actually measured that this helps. -Copy the boot scripts into `/etc/rc.d`: +### rc.conf -[[!template id=programlisting text=""" -# cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/ -"""]] +Ensure that the boot scripts installed in +`/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you +have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen, +but a normal part of pkgsrc usage.) -Enable `xencommons`: +Set `xencommons=YES` in rc.conf: [[!template id=filecontent name="/etc/rc.conf" text=""" xencommons=YES """]] +\todo Recommend for/against xen-watchdog. + +### Testing + Now, reboot so that you are running a DOM0 kernel under Xen, rather than GENERIC without Xen. -TODO: Recommend for/against xen-watchdog. - Once the reboot is done, use `xl` to inspect Xen's boot messages, available resources, and running domains. For example: @@ -196,83 +292,53 @@ the state when the new xenstored starts. make this work, one should not expect to be able to restart xenstored (and thus xencommons). There is currently no reason to expect that this will get fixed any time soon. +\todo Confirm if this is still true in 2020. -anita (for testing NetBSD) --------------------------- - -With the setup so far, one should be able to run -anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as -root, because anita must create a domU): - -[[!template id=programlisting text=""" -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 dom0 kernel compared to hardware. -One is that the module ABI is different because some of the #defines -change, so one must build modules for Xen. As of netbsd-7, the build -system does this automatically. +One is that through NetBSD 9 the module ABI is different because some +of the #defines change, so there are separate sets of modules in +/stand. In NetBSD-current, there is only one set of modules. The other difference is that XEN3_DOM0 does not have exactly the same options as GENERIC. While it is debatable whether or not this is a bug, users should be aware of this and can simply add missing config items if desired. -Updating NetBSD in a dom0 -------------------------- +Finally, there have been occasional reports of trouble with X11 +servers in NetBSD as a dom0. + +## Updating Xen in a dom0 + +Basically, update the xenkernel and xentools packages and copy the new +Xen kernel into place, and reboot. This procedure should be usable to +update to a new Xen release, but the reader is reminded that having a +non-Xen boot methods was recommended earlier. + +## Updating NetBSD in a dom0 This is just like updating NetBSD on bare hardware, assuming the new version supports the version of Xen you are running. Generally, one replaces the kernel and reboots, and then overlays userland binaries and adjusts `/etc`. -Note that one must update both the non-Xen kernel typically used for -rescue purposes and the DOM0 kernel used with Xen. +Note that one should update both the non-Xen kernel typically used for +rescue purposes, as well as the DOM0 kernel used with Xen. -Converting from grub to /boot ------------------------------ +## anita (for testing NetBSD) -These instructions were used to convert a system from -grub to /boot. The system was originally installed in February of -2006 with a RAID1 setup and grub to boot Xen 2, and has been updated -over time. Before these commands, it was running NetBSD 6 i386, Xen -4.1 and grub, much like the message linked earlier in the grub -section. +With a NetBSD dom0, even without any domUs, one should be able to run +anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as +root, because anita must create a domU): [[!template id=programlisting text=""" -# Install MBR bootblocks on both disks. -fdisk -i /dev/rwd0d -fdisk -i /dev/rwd1d -# Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components. -installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1 -installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1 -# Install secondary boot loader -cp -p /usr/mdec/boot / -# Create boot.cfg following earlier guidance: -menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M -menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M -menu=GENERIC:boot -menu=GENERIC single-user:boot -s -menu=GENERIC.ok:boot netbsd.ok -menu=GENERIC.ok single-user:boot netbsd.ok -s -menu=Drop to boot prompt:prompt -default=1 -timeout=30 -"""]] - -Upgrading Xen versions ---------------------- - -Minor version upgrades are trivial. Just rebuild/replace the -xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg` -references it), and reboot. +anita --vmm=xl test file:///usr/obj/i386/ +"""]] -#Unprivileged domains (domU) +# Unprivileged domains (domU) This section describes general concepts about domUs. It does not address specific domU operating systems or how to install them. The @@ -287,8 +353,7 @@ mediated by Xen, and configured in the d 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. -Config files ------------- +## Config files See /usr/pkg/share/examples/xen/xlexample* for a small number of well-commented examples, mostly for running @@ -315,6 +380,8 @@ are stored in files and Xen attaches the dom0 on domain creation. The system treats xbd0 as the boot device without needing explicit configuration. +There is not type line; that implicitly defines a pv domU. + By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note that "xl create" takes the name of a config file, while other commands take the name of a domain. @@ -334,8 +401,7 @@ equivalent to pushing the power button; power-press event and do a clean shutdown. Shutting down the dom0 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 of CPUs seen by the hypervisor. For a domU, it is controlled @@ -349,8 +415,7 @@ than the available memory. Xen also provides a "balloon" driver, which can be used to let domains use more memory temporarily. -Virtual disks -------------- +## Virtual disks In domU config files, the disks are defined as a sequence of 3-tuples: @@ -385,11 +450,7 @@ Note that NetBSD by default creates only than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the dom0. -Note that NetBSD by default creates only xbd[0123]. If you need more -virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU. - -Virtual Networking ------------------- +## Virtual Networking Xen provides virtual Ethernets, each of which connects the dom0 and a domU. For each virtual network, there is an interface "xvifN.M" in @@ -421,8 +482,7 @@ The MAC address specified is the one use domain. The interface in dom0 will use this address XOR'd with 00:00:00:01:00:00. Random MAC addresses are assigned if not given. -Starting domains automatically ------------------------------- +## Starting domains automatically To start domains `domU-netbsd` and `domU-linux` at boot and shut them down cleanly on dom0 shutdown, add the following in rc.conf: @@ -431,14 +491,14 @@ down cleanly on dom0 shutdown, add the f xendomains="domU-netbsd domU-linux" """]] -# Creating a domU +# domU setup for specific systems Creating domUs is almost entirely independent of operating system. We -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 presented the basics of config files in the previous system. + +Of course, this section presumes that you have a working dom0. -Creating a NetBSD PV domU --------------------------- +## Creating a NetBSD PV domU See the earlier config file, and adjust memory. Decide on how much storage you will provide, and prepare it (file or LVM). @@ -447,14 +507,14 @@ While the kernel will be obtained from t file should be present in the domU as /netbsd so that tools like savecore(8) can work. (This is helpful but not necessary.) -The kernel must be specifically for Xen and for use as a domU. The -i386 and amd64 provide the following kernels: +The kernel must be specifically built for Xen, to use PV interfacesas +a domU. NetBSD release builds provide the following kernels: i386 XEN3PAE_DOMU amd64 XEN3_DOMU This will boot NetBSD, but this is not that useful if the disk is -empty. One approach is to unpack sets onto the disk outside of xen +empty. One approach is to unpack sets onto the disk outside of Xen (by mounting it, just as you would prepare a physical disk for a system you can't run the installer on). @@ -474,11 +534,11 @@ line should be used in the config file. After booting the domain, the option to install via CDROM may be selected. The CDROM device should be changed to `xbd1d`. -Once done installing, "halt -p" the new domain (don't reboot or halt, +Once done installing, "halt -p" the new domain (don't reboot or halt: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the config file), switch the config file back to the XEN3_DOMU kernel, and start the new domain again. Now it should be able to use "root on -xbd0a" and you should have a, functional NetBSD domU. +xbd0a" and you should have a functional NetBSD domU. TODO: check if this is still accurate. When the new domain is booting you'll see some warnings about *wscons* @@ -494,12 +554,12 @@ and the pseudo-terminals. These can be f Finally, all screens must be commented out from `/etc/wscons.conf`. -It is also desirable to add - - powerd=YES - -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. +One should also run `powerd` in a domU, but this should not need +configuring. With powerd, the domain will run a controlled shutdown +if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via +receiving a synthetic `power button pressed` signal. In 9 and +current, `powerd` is run by default under Xen kernels (or if ACPI is +present), and it can be added to rc.conf if not. 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 @@ -509,8 +569,10 @@ not really a Xen-specific issue, but bec obtained from the dom0, it is far more likely to be out of sync or missing with Xen.) -Creating a Linux domU ---------------------- +Note that NetBSD by default creates only xbd[0123]. If you need more +virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU. + +## Creating a Linux domU Creating unprivileged Linux domains isn't much different from unprivileged NetBSD domains, but there are some details to know. @@ -563,16 +625,12 @@ Use type='pvh'. \todo Explain where the kernel comes from. - -Creating a Solaris domU ------------------------ +## Creating a Solaris domU See possibly outdated [Solaris domU instructions](/ports/xen/howto-solaris/). - -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 @@ -645,9 +703,20 @@ note that only the "xpci" lines are unus cd* at scsibus? target ? lun ? # SCSI CD-ROM drives -# Specific Issues +# Miscellaneous Information + +## Nesting under Linux KVM + +It is possible to run a Xen and a NetBSD dom0 under Linux KVM. One +can enable virtio in the dom0 for greater speed. -## domU +## Other nesting + +In theory, any full emulation should be able to run Xen and a NetBSD +dom0. The HOWTO does not currently have information about Xen XVM +mode, nvmm, qemu, Virtualbox, etc. + +## NetBSD 5 as domU [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html) (However, NetBSD 5 systems should be updated to a supported version.) @@ -702,8 +771,9 @@ NetBSD apparently only use specific vers \todo Explain better. -pvgrub ------- +## Boot methods + +### pvgrub 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 @@ -728,8 +798,7 @@ partition for the kernel with the intent which leads to /netbsd not being the actual kernel. One must remember to update the special boot partition. -pygrub -------- +### pygrub 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 @@ -743,7 +812,8 @@ historical DomU images using it still wo As of 2014, pygrub seems to be of mostly historical interest. New DomUs should use pvgrub. -Amazon ------- +## Specific Providers + +### Amazon See the [Amazon EC2 page](/amazon_ec2/).