QEMU v2.7 released

QEMU v2.7 is out! Here is a list of the highlights for KVM on z:

• Support for PCI passthrough devices is now fully functional for the first time. While we consider support as experimental, since there is still work to be done to utilize hardware acceleration facilities as well as further testing pending, attaching PCI devices directly to guests is now possible. Also note that while hot-plugging PCI devices is supported, hot-unplugging is not. Further limitations, e.g. for live guest migration, apply for now.
  We strictly recommend to use libvirt for all configuring, including PCI devices. Therefore, a step-by-step description of how to attach a PCI device to a KVM guest on z Systems will follow when the respective code becomes available in one of the next libvirt releases.
  
• Runtime instrumentation in KVM guests: IBM z13 and LinuxONE machines introduced a new hardware facility which allows to collect sampling data on code execution in CPUs at runtime. This data can be used by just-in-time compilers, like the one provided by IBM Java, to improve the generated code for better performance.
• IPL from any subchannel set: Prior to QEMU v2.7, KVM guests could only IPL/boot from devices with a subchannel set ID of 0. Once IPL'd, they could attach disks in any subchannel set just fine, but the IPL/boot from devices in subchannel sets 1-3 was not possible. With the addition of this feature, KVM guests can IPL from devices in all 4 subchannel sets.
  Here is a sample domain definition indicating the change:
  
    <disk type=’file’ device=’disk’>
      <driver name=’qemu’ type=’qcow2’/>
      <source file=’/var/lib/libvirt/images/guest.qcow2’/>
      <target dev=’vda’ bus=’virtio’/>
      <address type=’ccw’ cssid=’0xab’ ssid=’0x2’
               devno=’0x0037’/>
    </disk>