Chapter 16. Guest Virtual Machine Device Configuration

Procedure 16.3. Assigning a PCI device to a guest virtual machine with virsh

1. Identify the device

   First, identify the PCI device designated for device assignment to the virtual machine. Use the lspci command to list the available PCI devices. You can refine the output of lspci with grep.
   This example uses the Ethernet controller highlighted in the following output:

   # lspci | grep Ethernet
   00:19.0 Ethernet controller: Intel Corporation 82567LM-2 Gigabit Network Connection
   01:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
   01:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)

   This Ethernet controller is shown with the short identifier 00:19.0. We need to find out the full identifier used by virsh in order to assign this PCI device to a virtual machine.
   To do so, use the virsh nodedev-list command to list all devices of a particular type (pci) that are attached to the host machine. Then look at the output for the string that maps to the short identifier of the device you wish to use.
   This example shows the string that maps to the Ethernet controller with the short identifier 00:19.0. Note that the : and . characters are replaced with underscores in the full identifier.

   # virsh nodedev-list --cap pci
   pci_0000_00_00_0
   pci_0000_00_01_0
   pci_0000_00_03_0
   pci_0000_00_07_0
   pci_0000_00_10_0
   pci_0000_00_10_1
   pci_0000_00_14_0
   pci_0000_00_14_1
   pci_0000_00_14_2
   pci_0000_00_14_3
   pci_0000_00_19_0
   pci_0000_00_1a_0
   pci_0000_00_1a_1
   pci_0000_00_1a_2
   pci_0000_00_1a_7
   pci_0000_00_1b_0
   pci_0000_00_1c_0
   pci_0000_00_1c_1
   pci_0000_00_1c_4
   pci_0000_00_1d_0
   pci_0000_00_1d_1
   pci_0000_00_1d_2
   pci_0000_00_1d_7
   pci_0000_00_1e_0
   pci_0000_00_1f_0
   pci_0000_00_1f_2
   pci_0000_00_1f_3
   pci_0000_01_00_0
   pci_0000_01_00_1
   pci_0000_02_00_0
   pci_0000_02_00_1
   pci_0000_06_00_0
   pci_0000_07_02_0
   pci_0000_07_03_0

   Record the PCI device number that maps to the device you want to use; this is required in other steps.

2. Review device information

   Information on the domain, bus, and function are available from output of the virsh nodedev-dumpxml command:

   
   # virsh nodedev-dumpxml pci_0000_00_19_0
   <device>
     <name>pci_0000_00_19_0</name>
     <parent>computer</parent>
     <driver>
       <name>e1000e</name>
     </driver>
     <capability type='pci'>
       <domain>0</domain>
       <bus>0</bus>
       <slot>25</slot>
       <function>0</function>
       <product id='0x1502'>82579LM Gigabit Network Connection</product>
       <vendor id='0x8086'>Intel Corporation</vendor>
       <iommuGroup number='7'>
         <address domain='0x0000' bus='0x00' slot='0x19' function='0x0'/>
       </iommuGroup>
     </capability>
   </device>
   

   Figure 16.1. Dump contents

   Note

   An IOMMU group is determined based on the visibility and isolation of devices from the perspective of the IOMMU. Each IOMMU group may contain one or more devices. When multiple devices are present, all endpoints within the IOMMU group must be claimed for any device within the group to be assigned to a guest. This can be accomplished either by also assigning the extra endpoints to the guest or by detaching them from the host driver using virsh nodedev-detach. Devices contained within a single group may not be split between multiple guests or split between host and guest. Non-endpoint devices such as PCIe root ports, switch ports, and bridges should not be detached from the host drivers and will not interfere with assignment of endpoints.

   Devices within an IOMMU group can be determined using the iommuGroup section of the virsh nodedev-dumpxml output. Each member of the group is provided in a separate "address" field. This information may also be found in sysfs using the following:

   $ ls /sys/bus/pci/devices/0000:01:00.0/iommu_group/devices/

   An example of the output from this would be:

   0000:01:00.0  0000:01:00.1

   To assign only 0000.01.00.0 to the guest, the unused endpoint should be detached from the host before starting the guest:

   $ virsh nodedev-detach pci_0000_01_00_1

3. Determine required configuration details

   See the output from the virsh nodedev-dumpxml pci_0000_00_19_0 command for the values required for the configuration file.
   The example device has the following values: bus = 0, slot = 25 and function = 0. The decimal configuration uses those three values:

   bus='0'
   slot='25'
   function='0'

4. Add configuration details

   Run virsh edit, specifying the virtual machine name, and add a device entry in the <devices> section to assign the PCI device to the guest virtual machine. For example:

   # virsh edit guest1-rhel7-64

   
   <devices>
   	[...]
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
         <address domain='0' bus='0' slot='25' function='0'/>
      </source>
    </hostdev>
    [...]
   </devices>
   

   Figure 16.2. Add PCI device

   Alternately, run virsh attach-device, specifying the virtual machine name and the guest's XML file:

   virsh attach-device guest1-rhel7-64 file.xml

   Note

   PCI devices may include an optional read-only memory (ROM) module, also known as an option ROM or expansion ROM, for delivering device firmware or pre-boot drivers (such as PXE) for the device. Generally, these option ROMs also work in a virtualized environment when using PCI device assignment to attach a physical PCI device to a VM.

   However, in some cases, the option ROM can be unnecessary, which may cause the VM to boot more slowly, or the pre-boot driver delivered by the device can be incompatible with virtualization, which may cause the guest OS boot to fail. In such cases, Red Hat recommends masking the option ROM from the VM. To do so:

   1. On the host, verify that the device to assign has an expansion ROM base address register (BAR). To do so, use the lspci -v command for the device, and check the output for a line that includes the following:

      Expansion ROM at

   2. Add the <rom bar='off'/> element as a child of the <hostdev> element in the guest's XML configuration:

      <hostdev mode='subsystem' type='pci' managed='yes'>
        <source>
           <address domain='0' bus='0' slot='25' function='0'/>
        </source>
        <rom bar='off'/>
      </hostdev>
      

5. Start the virtual machine

   # virsh start guest1-rhel7-64

Procedure 16.4. Assigning a PCI device to a guest virtual machine using virt-manager

1. Open the hardware settings

   Open the guest virtual machine and click the Add Hardware button to add a new device to the virtual machine.
   

   Figure 16.3. The virtual machine hardware information window

2. Select a PCI device

   Select PCI Host Device from the Hardware list on the left.
   Select an unused PCI device. Note that selecting PCI devices presently in use by another guest causes errors. In this example, a spare audio controller is used. Click Finish to complete setup.
   

   Figure 16.4. The Add new virtual hardware wizard

3. Add the new device

   The setup is complete and the guest virtual machine now has direct access to the PCI device.
   

   Figure 16.5. The virtual machine hardware information window

Procedure 16.5. Assigning a PCI device to a virtual machine with virt-install

1. Identify the device

   Identify the PCI device designated for device assignment to the guest virtual machine.

   # lspci | grep Ethernet
   00:19.0 Ethernet controller: Intel Corporation 82567LM-2 Gigabit Network Connection
   01:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
   01:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)

   The virsh nodedev-list command lists all devices attached to the system, and identifies each PCI device with a string. To limit output to only PCI devices, enter the following command:

   # virsh nodedev-list --cap pci
   pci_0000_00_00_0
   pci_0000_00_01_0
   pci_0000_00_03_0
   pci_0000_00_07_0
   pci_0000_00_10_0
   pci_0000_00_10_1
   pci_0000_00_14_0
   pci_0000_00_14_1
   pci_0000_00_14_2
   pci_0000_00_14_3
   pci_0000_00_19_0
   pci_0000_00_1a_0
   pci_0000_00_1a_1
   pci_0000_00_1a_2
   pci_0000_00_1a_7
   pci_0000_00_1b_0
   pci_0000_00_1c_0
   pci_0000_00_1c_1
   pci_0000_00_1c_4
   pci_0000_00_1d_0
   pci_0000_00_1d_1
   pci_0000_00_1d_2
   pci_0000_00_1d_7
   pci_0000_00_1e_0
   pci_0000_00_1f_0
   pci_0000_00_1f_2
   pci_0000_00_1f_3
   pci_0000_01_00_0
   pci_0000_01_00_1
   pci_0000_02_00_0
   pci_0000_02_00_1
   pci_0000_06_00_0
   pci_0000_07_02_0
   pci_0000_07_03_0

   Record the PCI device number; the number is needed in other steps.
   Information on the domain, bus and function are available from output of the virsh nodedev-dumpxml command:

   # virsh nodedev-dumpxml pci_0000_01_00_0

   
   <device>
     <name>pci_0000_01_00_0</name>
     <parent>pci_0000_00_01_0</parent>
     <driver>
       <name>igb</name>
     </driver>
     <capability type='pci'>
       <domain>0</domain>
       <bus>1</bus>
       <slot>0</slot>
       <function>0</function>
       <product id='0x10c9'>82576 Gigabit Network Connection</product>
       <vendor id='0x8086'>Intel Corporation</vendor>
       <iommuGroup number='7'>
         <address domain='0x0000' bus='0x00' slot='0x19' function='0x0'/>
       </iommuGroup>
     </capability>
   </device>
   

   Figure 16.6. PCI device file contents

   Note

   If there are multiple endpoints in the IOMMU group and not all of them are assigned to the guest, you will need to manually detach the other endpoint(s) from the host by running the following command before you start the guest:

   $ virsh nodedev-detach pci_0000_00_19_1

   See the Note in Section 16.1.1, “Assigning a PCI Device with virsh” for more information on IOMMU groups.

2. Add the device

   Use the PCI identifier output from the virsh nodedev command as the value for the --host-device parameter.

   virt-install \
   --name=guest1-rhel7-64 \
   --disk path=/var/lib/libvirt/images/guest1-rhel7-64.img,size=8 \
   --vcpus=2 --ram=2048 \
   --location=http://example1.com/installation_tree/RHEL7.0-Server-x86_64/os \
   --nonetworks \
   --os-type=linux \
   --os-variant=rhel7
   --host-device=pci_0000_01_00_0

3. Complete the installation

   Complete the guest installation. The PCI device should be attached to the guest.

Procedure 16.6. Detaching a PCI device from a guest with virsh

1. Detach the device

   Use the following command to detach the PCI device from the guest by removing it in the guest's XML file:

   # virsh detach-device name_of_guest file.xml

2. Re-attach the device to the host (optional)

   If the device is in managed mode, skip this step. The device will be returned to the host automatically.
   If the device is not using managed mode, use the following command to re-attach the PCI device to the host machine:

   # virsh nodedev-reattach device

   For example, to re-attach the pci_0000_01_00_0 device to the host:

   # virsh nodedev-reattach pci_0000_01_00_0

   The device is now available for host use.

Procedure 16.7. Detaching a PCI Device from a guest with virt-manager

1. Open the virtual hardware details screen

   In virt-manager, double-click the virtual machine that contains the device. Select the Show virtual hardware details button to display a list of virtual hardware.
   

   Figure 16.7. The virtual hardware details button

2. Select and remove the device

   Select the PCI device to be detached from the list of virtual devices in the left panel.
   

   Figure 16.8. Selecting the PCI device to be detached

   Click the Remove button to confirm. The device is now available for host use.