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13.8. Attaching DASD devices to virtual machines on IBM Z

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Using the vfio-ccw feature, you can assign direct-access storage devices (DASDs) as mediated devices to your virtual machines (VMs) on IBM Z hosts. This for example makes it possible for the VM to access a z/OS dataset, or to provide the assigned DASDs to a z/OS machine.

Conditions préalables

  • Your host system is using the IBM Z hardware architecture and supports the FICON protocol.
  • The target VM is using a Linux guest operating system.

  • The driverctl package is installed. 

    # dnf install driverctl

  • The necessary kernel modules have been loaded on the host. To verify, use: 

    # lsmod | grep vfio

    The output should contain the following modules:

    • vfio_ccw
    • vfio_mdev
    • vfio_iommu_type1

  • You have a spare DASD device for exclusive use by the VM, and you know the device’s identifier.

    This procedure uses 0.0.002c as an example. When performing the commands, replace 0.0.002c with the identifier of your DASD device.

Procédure

  1. Obtain the subchannel identifier of the DASD device. 

    # lscss -d 0.0.002c
Device   Subchan.  DevType CU Type Use  PIM PAM POM  CHPIDs
----------------------------------------------------------------------
0.0.002c 0.0.29a8  3390/0c 3990/e9 yes  f0  f0  ff   02111221 00000000

    In this example, the subchannel identifier is detected as 0.0.29a8. In the following commands of this procedure, replace 0.0.29a8 with the detected subchannel identifier of your device.

  2. If the lscss command in the previous step only displayed the header output and no device information, perform the following steps:

    1. Remove the device from the cio_ignore list. 

      # cio_ignore -r 0.0.002c

    2. In the guest OS, edit the kernel command line of the VM and add the device identifier with a ! mark to the line that starts with cio_ignore=, if it is not present already. 

      cio_ignore=all,!condev,!0.0.002c
    3. Repeat step 1 on the host to obtain the subchannel identifier.

  3. Bind the subchannel to the vfio_ccw passthrough driver. 

    # driverctl -b css set-override 0.0.29a8 vfio_ccw
    Note

    This binds the 0.0.29a8 subchannel to vfio_ccw persistently, which means the DASD will not be usable on the host. If you need to use the device on the host, you must first remove the automatic binding to 'vfio_ccw' and rebind the subchannel to the default driver:

    # driverctl -b css unset-override 0.0.29a8

  4. Generate an UUID. 

    # uuidgen
30820a6f-b1a5-4503-91ca-0c10ba12345a

  5. Define and start the DASD mediated device. 

    # cat nodedev.xml
<device>
    <parent>css_0_0_29a8</parent>
    <capability type="mdev">
        <type id="vfio_ccw-io"/>
        <uuid>30820a6f-b1a5-4503-91ca-0c10ba12345a</uuid>
    </capability>
</device>

# virsh nodedev-define nodedev.xml
Node device 'mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8' defined from 'nodedev.xml'

# virsh nodedev-start mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8
Device mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8 started
  6. Shut down the VM, if it is running.

  7. Attach the mediated device to the VM. To do so, use the virsh edit utility to edit the XML configuration of the VM, add the following section to the XML, and replace the uuid value with the UUID you generated in the previous step. 

    <hostdev mode='subsystem' type='mdev' model='vfio-ccw'>
  <source>
    <address uuid="30820a6f-b1a5-4503-91ca-0c10ba12345a"/>
  </source>
</hostdev>

  8. Optional: Configure the mediated device to start automatically on host boot. 

    # virsh nodedev-autostart mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8

Vérification

  1. Ensure that the mediated device is configured correctly. 

    # virsh nodedev-info mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8
Name:           mdev_30820a6f_b1a5_4503_91ca_0c10ba12345a_0_0_29a8
Parent:         css_0_0_0121
Active:         yes
Persistent:     yes
Autostart:      yes

  2. Obtain the identifier that libvirt assigned to the mediated DASD device. To do so, display the XML configuration of the VM and look for a vfio-ccw device. 

    # virsh dumpxml vm-name

<domain>
[...]
    <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-ccw'>
      <source>
        <address uuid='10620d2f-ed4d-437b-8aff-beda461541f9'/>
      </source>
      <alias name='hostdev0'/>
      <address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0009'/>
    </hostdev>
[...]
</domain>

    In this example, the assigned identifier of the device is 0.0.0009.

  3. Start the VM and log in to its guest OS.

  4. In the guest OS, confirm that the DASD device is listed. For example: 

    # lscss | grep 0.0.0009
0.0.0009 0.0.0007  3390/0c 3990/e9      f0  f0  ff   12212231 00000000

  5. In the guest OS, set the device online. For example: 

    # chccwdev -e 0.0009
Setting device 0.0.0009 online
Done

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