Friday, October 28, 2016

KVM for IBM z Systems v1.1.2 released

KVM for IBM z Systems v1.1.2 is out today! See here for the respective blog post on Mainframe Insights, and the following pages for the formal announcements: US, Canada, Asia-Pacific, Japan, Latin America and Europe.

It ships with QEMU v2.6 and libvirt v1.3.3. Here is a list of highlights from a KVM on z perspective:
  • Enhanced SCA support
    Exploit up to 248 CPUs per KVM guest
  • SIE capability
    Expose SIE availability in /proc/cpuinfo as follows:

       $ cat /proc/cpuinfo | grep features
       features        : esan3 zarch stfle msa ldisp eimm dfp edat etf3eh
                         highgprs te vx sie
  • STP host toleration
    Previously, Server Time Protocol (STP) had to be turned off in the host. In case of time differences, the TOD clock is adjusted in a smooth manner, avoiding jumps.
  • Improved removable media support
    Allow to boot KVM guests seamlessly from ISO9660 media.
  • OASIS VIRTIO v1.0 support
    Support OASIS OASIS standard for virtio devices.
  • CPU hotplugging
    Allow to add CPUs dynamically to a running guest
  • STHYI support: Added the z/VM-defined Store Hypervisor Information instruction (STHYI) for KVM guests. See also here.

Thursday, October 6, 2016

Linux kernel 4.8 released

Linux kernel 4.8 (available here) has been released, here are the highlights in support of KVM on z:

Nested Virtualization
This feature allows to start further KVM hosts within KVM guests, also called second level virtualization. As a prerequisite, it requires a recent, post-2.7 version of QEMU including the s390 CPU models (assumed to be included in the forthcoming QEMU 2.8 release).
Nested virtualization is currently turned off per default, and has to be enabled when loading the kvm module:

   [root ~]# modprobe kvm nested=1

or by appending kvm.nested=1 to the kernel command line.
When starting QEMU, make sure to chose the right machine ("s390-ccw-virtio-2.8" or higher) in the domain xml's os element for the guest:

      <type arch='s390x' machine='s390-ccw-virtio-2.8'>hvm</type>
      <boot dev='hd'/>

Finally, verify in a KVM guest that hosting further KVM guests is possible, as indicated by flag "sie" in /proc/cpuinfo as follows:

   [root ~]# cat /proc/cpuinfo | grep features
   features        : esan3 zarch stfle msa ldisp eimm dfp
edat etf3eh
                     highgprs te vx sie

STHYI Instruction available for KVM Guests
Linux kernel 4.8 saw the inclusion of an implementation of the STHYI (Store Hypervisor Information) instruction. Using Linux kernel 4.8 for the host will make the STHYI instruction available to all KVM guests of that host.
Previously available on z/VM only, this instruction provides detailed information on CPU resources on various levels (machine, LPAR, hypervisor, guest, etc.).

Use qclib to access the information. Also see this blog post for further details regarding qclib and KVM on z.