--- wikisrc/ports/xen/howto.mdwn 2016/12/20 19:59:38 1.132 +++ wikisrc/ports/xen/howto.mdwn 2017/01/04 10:25:16 1.139 @@ -81,6 +81,11 @@ of Xen version and NetBSD version. This which version to choose. Versions not in pkgsrc and older unsupported versions of NetBSD are intentionally ignored. +The term "amd64" is used to refer to both the NetBSD port and to the +hardware architecture on which it runs. (Such hardware is made by +both Intel and AMD, and in 2016 a normal PC has this CPU +architecture.) + Xen --- @@ -89,38 +94,44 @@ xenkernel and xentools. We will refer o but note that both packages must be installed together and must have matching versions. -xenkernel3 provides Xen 3.1. It is no longer maintained by Xen, and the last applied security patch was in -2011. Thus, it should not be used. It supports PCI passthrough, -which is why people use it anyway. Xen 3.1 supports i386, both PAE and -non-PAE. +xenkernel3 provides Xen 3.1. It is no longer maintained by Xen, and +the last applied security patch was in 2011. Thus, it should not be +used. It supports PCI passthrough, which is why people use it anyway. +Xen 3.1 runs on i386 (both non-PAE and PAE) and amd64 hardware. xenkernel33 provides Xen 3.3. It is no longer maintained by Xen, and the last applied security patch was in 2012. Thus, it should not be -used. Xen 3.3 supports i386, but only in PAE mode. There are no good +used. Xen 3.3 runs on i386 PAE and amd64 hardware. There are no good reasons to run this version. xenkernel41 provides Xen 4.1. It is no longer maintained by Xen, but -as of 2016-12 received backported security patches. Xen 4.1 supports -i386, but only in PAE mode. There are no good reasons to run this +as of 2016-12 received backported security patches. Xen 4.1 runs on +i386 PAE and amd64 hardware. There are no good reasons to run this version. +Note that 3.1, 3.3 and 4.1 have been removed from pkgsrc-current, but +are in 2016Q4. They will be removed from this HOWTO sometime after +2017Q1. + xenkernel42 provides Xen 4.2. It is no longer maintained by Xen, but -as of 2016-12 received backported security patches. Xen 4.2 supports -i386, but only in PAE mode. The only reason to run this is if you -need to use xm instead of xl, or if you need to run an i386 dom0 -(because your hardware is i386 only). +as of 2016-12 received backported security patches. Xen 4.2 runs on +i386 PAE and amd64 hardware. The only reason to run this is if you +need to use xm instead of xl, or if you need to run on hardware that +supports i386 but not amd64. (This might also be useful if you need +an i386 dom0, if it turns out that an amd64 Xen kernel and an i386 +dom0 is problematic.) xenkernel45 provides Xen 4.5. As of 2016-12, security patches were -released by Xen and applied to pkgsrc. Xen 4.5 requires using a dom0 -running NetBSD's amd64 port (Intel or AMD hardware is fine), but domUs -can be amd64 or i386 PAE. While slightly old, n4.5 has been tested and -run by others, so it is the conservative choice. +released by Xen and applied to pkgsrc. Xen 4.5 runs on amd64 hardware +only. While slightly old, 4.5 has been tested and run by others, so +it is the conservative choice. xenkernel46 provides Xen 4.6. It is new to pkgsrc as of 2016-05. As of 2016-12, security patches were released by Xen and applied to -pkgsrc. Xen 4.6 similarly requires a NetBSD/amd64 dom0, but domUs can -be amd64 or i386 PAE. For new installations, 4.6 is probably the -appropriate choice and it will likely soon be the standard approach. +pkgsrc. Xen 4.6 runs on amd64 hardware only For new installations, +4.6 is probably the appropriate choice and it will likely soon be the +standard approach. (If using Ubuntu guests, be sure to have the +xentools46 from December, 2016). Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in pkgsrc. @@ -144,7 +155,7 @@ only which command you use, but the comm xentools packages provide xm for 3.1, 3.3 and 4.1 and xl for 4.2 and up. In 4.2, you can choose to use xm by simply changing the ctl_command -variable. +variable and setting xend=YES in rc.conf. With xl, virtual devices are configured in parallel, which can cause problems if they are written assuming serial operation (e.g., updating @@ -178,30 +189,43 @@ when using a dom0 as a normal computer.) Architecture ------------ -Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen +Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen versions). (Practically, almost any computer where one would want to run Xen today supports amd64.) -Xen, the dom0 kernel, and each domU kernel can be either i386 or -amd64. When building a xenkernel package, one obtains i386 on an i386 -host, and amd64 on an amd64 host. If the Xen kernel is i386, then the -dom0 kernel and all domU kernels must be i386. With an amd64 Xen -kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0 -kernel should in theory work. An amd64 Xen/dom0 is known to support -both i386PAE and amd64 domUs. - -i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are -built by default. (Note that emacs (at least) fails if run on i386 -with PAE when built without, and vice versa, presumably due to bugs in -the undump code.) - -Because of the above, the standard approach is to use amd64 for the -dom0. - -Xen 4.2 is the last version to support i386 as a host. TODO: Clarify -if this is about the CPU, the Xen kernel, or the dom0 kernel having to -be amd64. - +Xen, the dom0 system, and each domU system can be either i386 or +amd64. When building a xenkernel package, one obtains an i386 Xen +kernel on an i386 host, and an amd64 Xen kernel on an amd64 host. If +the Xen kernel is i386, then the dom0 kernel and all domU kernels must +be i386. With an amd64 Xen kernel, an amd64 dom0 kernel is known to +work, and an i386 dom0 kernel should in theory work. An amd64 +Xen/dom0 is known to support both i386 and amd64 domUs. + +i386 dom0 and domU kernels must be PAE (except for an i386 Xen 3.1 +kernel, where one can use non-PAE for dom0 and all domUs); PAE kernels +are included in the NetBSD default build. (Note that emacs (at least) +fails if run on i386 with PAE when built without, and vice versa, +presumably due to bugs in the undump code.) + +Because of the above, the standard approach is to use an amd64 Xen +kernel and NetBSD/amd64 for the dom0. For domUs, NetBSD/i386 (with +the PAE kernel) and NetBSD/amd64 are in widespread use, and there is +little to no Xen-specific reason to prefer one over the other. + +Note that to use an i386 dom0 with Xen 4.5 or higher, one must build +(or obtain from pre-built packages) an amd64 Xen kernel and install +that on the system. (One must also use a PAE i386 kernel, but this is +also required with an i386 Xen kernel.). Almost no one in the +NetBSD/Xen community does this, and the standard, well-tested, +approach is to use an amd64 dom0. + +A [posting on +xen-devel](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) +explained that PV system call overhead was higher on amd64, and thus +there is some notion that i386 guests are faster. It goes on to +caution that the total situation is complex and not entirely +understood. On top of that caution, the post is about Linux, not +NetBSD. TODO: Include link to benchmarks, if someone posts them. Stability --------- @@ -224,6 +248,14 @@ xl, the NetBSD 7 stable branch, and to u dom0. Either the i386PAE or amd64 version of NetBSD may be used as domUs. +Because bugs are fixed quite often, and because of Xen security +advisories, it is good to stay up to date with NetBSD (tracking a +stable branch), with the Xen kernel (tracking a Xen version via +pkgsrc), and with the Xen tools. Specifically, NetBSD (-7 and +-current) got an important fix affecting dom0/domU timesharing in +November, 2015, and xentools46 got a fix to enable Ubuntu guests to +boot in December, 2016. + Status ------ @@ -239,7 +271,8 @@ The following table gives status, with t (generally on the most recent quarterly branch). The first code is "builds" if it builds ok, and "FAIL" for a failure to build. The second code/date only appears for xenkernel* and is "works" if it runs -ok as a dom0, and "FAIL" if it won't boot or run a domU. +ok as a dom0 and can support a domU, and "FAIL" if it won't boot or +run a domU. xenkernel3 netbsd-6 i386 FAIL 201612 xenkernel33 netbsd-6 i386 FAIL 201612 @@ -295,7 +328,10 @@ configuration. For experimenting with Xen, a machine with as little as 1G of RAM and 100G of disk can work. For running many domUs in productions, far -more will be needed. +more will be needed; e.g. 4-8G and 1T of disk is reasonable for a +half-dozen domUs of 512M and 32G each. Basically, the RAM and disk +have to be bigger than the sum of the RAM/disk needs of the dom0 and +all the domUs. Styles of dom0 operation ------------------------ @@ -382,13 +418,13 @@ releasedir/i386/binary/kernel/netbsd-XEN should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and typically are) left compressed. -In a dom0 kernel, kernfs is mandatory for xend to communicate with the -kernel, so ensure that /kern is in fstab. TODO: Say this is default, -or file a PR and give a reference. +In a dom0, kernfs is mandatory for xend to communicate with the +kernel, so ensure that /kern is in fstab. (A standard NetBSD install +should already mount /kern.) Because you already installed NetBSD, you have a working boot setup with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the -beginning of your root file system, /boot present, and likely +beginning of your root file system, have /boot, and likely also /boot.cfg. (If not, fix before continuing!) Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an @@ -399,11 +435,16 @@ example. The basic line is which specifies that the dom0 should have 256M, leaving the rest to be allocated for domUs. To use a serial console, use - menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1 + menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1 which will use the first serial port for Xen (which counts starting -from 1), forcing speed/parity, and also for NetBSD (which counts -starting at 0). In an attempt to add performance, one can also add +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). + +In an attempt to add performance, one can also add dom0_max_vcpus=1 dom0_vcpus_pin @@ -433,13 +474,14 @@ Using grub (historic) Before NetBSD's native bootloader could support Xen, the use of grub was recommended. If necessary, see the -[old grub information](/ports/xen/howto-grub/). +[old grub information](/ports/xen/howto-grub). The [HowTo on Installing into RAID-1](http://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html) explains how to set up booting a dom0 with Xen using grub with NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native -boot.) +boot. Now, just create a system with RAID-1, and alter /boot.cfg as +described above.) Configuring Xen ---------------