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version 1.154, 2018/07/26 16:29:45 version 1.155, 2018/08/01 13:19:43
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 Introduction  Introduction
 ============  ============
   
 [![[Xen  
 screenshot]](https://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](https://www.netbsd.org/gallery/in-Action/hubertf-xen.png)  
   
 Xen is a hypervisor for x86 hardware, which supports running multiple guest  Xen is a hypervisor for x86 hardware, which supports running multiple guest
 operating systems on a single physical machine.  Xen is a Type 1 or  operating systems on a single physical machine.  Xen is a Type 1 or
 bare-metal hypervisor; one uses the Xen kernel to control the CPU,  bare-metal hypervisor; one uses the Xen kernel to control the CPU,
Line 31  guests must be specifically coded for Xe Line 28  guests must be specifically coded for Xe
 modification is required; however, hardware support is required, such  modification is required; however, hardware support is required, such
 as VT-x on Intel CPUs and SVM on AMD CPUs.  as VT-x on Intel CPUs and SVM on AMD CPUs.
   
 There are further features for IOMMU virtualization, Intel's VT-d and  
 AMD's AMD-Vi.  TODO: Explain whether Xen on NetBSD makes use of these  
 features.  TODO: Review by someone who really understands this.  
   
 At 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.)
Line 83  See also the [Xen Security Advisory page Line 76  See also the [Xen Security Advisory page
   
 Note: Xen 4.2 was the last version to support 32bit CPUs.  Note: Xen 4.2 was the last version to support 32bit CPUs.
   
 Xen command program  
 -------------------  
   
 Early Xen used a program called xm to manipulate the system from the  
 dom0.  Starting in 4.1, a replacement program with similar behavior  
 called xl is provided, but it does not work well in 4.1.  In 4.2, both  
 xm and xl work fine.  4.4 is the last version that has xm.  
   
 You must make a global choice to use xm or xl, because it affects not  
 only which command you use, but the command used by rc.d scripts  
 (specifically xendomains) and which daemons should be run.  The  
 xentools packages provide xl for 4.2 and up.  
   
 In 4.2, you can choose to use xm by simply changing the ctl_command  
 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  
 firewall rules without explicit locking).  There is now locking for  
 the provided scripts, which works for normal casses (e.g, file-backed  
 xbd, where a vnd must be allocated).  But, as of 201612, it has not  
 been adequately tested for a complex custom setup with a large number  
 of interfaces.  
   
 NetBSD versions  NetBSD versions
 ---------------  ---------------
   
 The netbsd-7, netbsd-8, and -current branches are all reasonable  
 choices, with more or less the same considerations for non-Xen use.  
 NetBSD 8 is recommended as the stable version of the most recent  NetBSD 8 is recommended as the stable version of the most recent
 release for production use.  release for production use.
   
Line 128  because the hypercall interface has rema Line 95  because the hypercall interface has rema
 Architecture  Architecture
 ------------  ------------
   
 Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen  Xen itself runs on amd64 hardware. Practically, almost any computer
 versions).  Practically, almost any computer where one would want to  where one would want to run Xen today supports amd64.
 run Xen today supports amd64.  
   The dom0 system, plus each domU, can be either i386PAE or amd64.
 Xen, the dom0 system, and each domU system can be either i386 or  i386 without PAE is not supported.
 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 standard approach is to use NetBSD/amd64 for the dom0.  For domUs,
 the Xen kernel is i386, then the dom0 kernel and all domU kernels must  NetBSD/i386 (PAE) and NetBSD/amd64 are in widespread use, and there is
 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. PAE kernels are included in  
 the NetBSD default build.  
   
 Because of the above, the standard approach is to use an amd64 Xen  
 kernel and NetBSD/amd64 for the dom0.  For domUs, NetBSD/i386 (PAE) and  
 NetBSD/amd64 are in widespread use, and there is  
 little to no Xen-specific reason to prefer one over the other.  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  Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
Line 159  explained that PV system call overhead w Line 116  explained that PV system call overhead w
 there is some notion that i386 guests are faster.  It goes on to  there is some notion that i386 guests are faster.  It goes on to
 caution that the total situation is complex and not entirely  caution that the total situation is complex and not entirely
 understood. On top of that caution, the post is about Linux, not  understood. On top of that caution, the post is about Linux, not
 NetBSD.  TODO: Include link to benchmarks, if someone posts them.  NetBSD.
   
 NetBSD as a dom0  NetBSD as a dom0
 ================  ================
Line 245  HOWTO page.) Line 202  HOWTO page.)
 Installation of Xen  Installation of Xen
 -------------------  -------------------
   
 In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from  We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as
 pkgsrc (or another matching pair).  See [the pkgsrc  dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
 documentation](https://www.NetBSD.org/docs/pkgsrc/) for help with  Ensure that your packages are recent.
 pkgsrc.  Ensure that your packages are recent; the HOWTO does not  
 contemplate old builds.  Once this is done, install the Xen kernel itself:
   
 Next you need to install the selected Xen kernel itself, which is  [[!template id=programlisting text="""
 installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.  # cp /usr/pkg/xen48-kernel/xen.gz /
 For debugging, one may copy xen-debug.gz; this is conceptually similar  """]]
 to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only  
 useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel  Then, place a NetBSD XEN3_DOM0 kernel in /, copied from
 in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz  releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz of a NetBSD build.
 of a NetBSD build.  If using i386, use  
 releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  Both xen and  
 the NetBSD kernel may be (and typically are) left compressed.  
   
 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, have /boot, and likely also  
 /boot.cfg.  (If not, fix before continuing!)  
   
 Add a line to /boot.cfg to boot Xen.  See boot.cfg(5) for an  Add a line to /boot.cfg to boot Xen:
 example.  The basic line is:  
   
 [[!template id=programlisting text="""  [[!template id=programlisting text="""
 menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M  menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
 """]]  """]]
   
 which specifies that the dom0 should have 512M, leaving the rest to be  which specifies that the dom0 should have 512MB of ram, leaving the rest
 allocated for domUs.  To use a serial console, use  to be allocated for domUs.  To use a serial console, use
   
 [[!template id=programlisting text="""  [[!template id=programlisting text="""
 menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1  menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
Line 298  dom0_max_vcpus=1 dom0_vcpus_pin Line 242  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.  TODO: benchmark this.  more) and to pin that vcpu to a physical CPU.
   
 Xen has [many boot  Xen has [many boot
 options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),  options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),
Line 306  and other than dom0 memory and max_vcpus Line 250  and other than dom0 memory and max_vcpus
 necessary.  necessary.
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  As with non-Xen systems, you should have a line to boot /netbsd (a
 kernel that works without Xen).  Consider a line to boot /netbsd.ok (a  kernel that works without Xen).
 fallback version of the non-Xen kernel, updated manually when you are  
 sure /netbsd is ok).  Consider also a line to boot fallback versions  
 of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used  
 to resolve Xen booting issues.  
   
 Now, reboot so that you are running a DOM0 kernel under Xen, rather  Now, reboot so that you are running a DOM0 kernel under Xen, rather
 than GENERIC without Xen.  than GENERIC without Xen.
Removed from v.1.154  
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