LookingGlass/doc/ivshmem_kvmfr.rst

:orphan:
.. _ivshmem_kvmfr:

IVSHMEM with the KVMFR module (Recommended)
###########################################

The kernel module implements a basic interface to the IVSHMEM device
for Looking Glass allowing DMA GPU transfers.

.. _ivshmem_kvmfr_prereq:

Prerequisites
-------------

The Linux kernel headers for your kernel version are required for building
along with `dkms` to manage the module when you upgrade your kernel.

.. code:: bash

   apt-get install linux-headers-$(uname -r) dkms

Then switch to the ``module/`` directory

.. code:: bash

   cd module/

.. _ivshmem_kvmfr_dkms:

Installing
~~~~~~~~~~

To install the module into DKMS, run

.. code:: bash

   dkms install "."

.. _ivshmem_kvmfr_loading:

Loading
~~~~~~~

Using the value you should have already calculated as per
:ref:`Determining Memory <libvirt_determining_memory>`, simply use
``modprobe`` with the parameter ``static_size_mb``, for example:

.. code:: bash

   modprobe kvmfr static_size_mb=32

Alternatively you can make this setting permanent by creating the file
``/etc/modprobe.d/kvmfr.conf`` with the following content.

.. code:: text

   options kvmfr static_size_mb=32

After this has been done, simply running ``modprobe kvmfr`` is all that is
required.

.. note::

   Don't forget to adjust ``static_size_mb`` to your needs.

.. _ivshmem_kvmfr_systemd:

systemd-modules-load
~~~~~~~~~~~~~~~~~~~~

For convenience, you may load the KVMFR module when starting your computer.
We can use the ``systemd-modules-load.service(8)`` service for this task.

Create the file ``/etc/modules-load.d/kvmfr.conf`` with the following
contents::

   # KVMFR Looking Glass module
   kvmfr

This will now run the next time you start your machine.

.. _ivshmem_kvmfr_verification:

Verification
~~~~~~~~~~~~

If everything has been done correctly you should see the following output in
dmesg:

.. code:: text

   kvmfr: creating 1 static devices

You should now also have the character device ``/dev/kvmfr0``

.. code:: bash

   $ ls -l /dev/kvmfr0
   crw------- 1 root root 242, 0 Mar  5 05:53 /dev/kvmfr0

.. warning::

   If you start the VM prior to loading the module, QEMU will create the file
   ``/dev/kvmfr0`` as a regular file. You can confirm if this has happened by
   running ``ls -l /dev/kvmfr0`` and checking if the file size is greater then
   zero, or the permissions do not start with ``c``. If this has occurred, you
   must delete the file and reload the module.

.. _ivhsmem_kvmfr_permissions:

Permissions
~~~~~~~~~~~

The module will create the ``/dev/kvmfr0`` node, which represents the KVMFR
interface. To use the interface, you need permission to access it by either
creating a udev rule to ensure your user can read and write to it, or simply
change its ownership manually, i.e.:

.. code:: bash

   sudo chown user:kvm /dev/kvmfr0

As an example, you can create a new file in ``/etc/udev/rules.d/99-kvmfr.rules``
with the following contents::

   SUBSYSTEM=="kvmfr", OWNER="user", GROUP="kvm", MODE="0660"

(replace ``user`` with your username)

.. _ivshmem_kvmfr_libvirt:

libvirt
~~~~~~~

Starting with QEMU 6.2 and libvirt 7.9, JSON style QEMU configuration is the
default syntax. Users running QEMU 6.2 or later **and** libvirt 7.9 or later,
should use this XML block to configure their VM for kvmfr:

.. code:: xml

   <qemu:commandline>
     <qemu:arg value='-device'/>
     <qemu:arg value='{"driver":"ivshmem-plain","id":"shmem0","memdev":"looking-glass"}'/>
     <qemu:arg value='-object'/>
     <qemu:arg value='{"qom-type":"memory-backend-file","id":"looking-glass","mem-path":"/dev/kvmfr0","size":33554432,"share":true}'/>
   </qemu:commandline>

.. note::

   -  The ``"size"`` tag represents the size of the shared memory device in
      bytes. Once you determine the proper size of the device as per
      :ref:`Determining Memory <libvirt_determining_memory>`, use the figure you
      got to calculate the size in bytes:

     ``size_in_MB x 1024 x 1024 = size_in_bytes``

If you are running QEMU older than 6.2 or libvirt older than 7.9, please use
legacy syntax for IVSHMEM setup:

.. code:: xml

   <qemu:commandline>
     <qemu:arg value='-device'/>
     <qemu:arg value='ivshmem-plain,id=shmem0,memdev=looking-glass'/>
     <qemu:arg value='-object'/>
     <qemu:arg value='memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=32M,share=yes'/>
   </qemu:commandline>

.. note::

   -  Using the legacy syntax on QEMU 6.2/libvirt 7.9 may cause QEMU to
      abort with the following error message:
      "``error: internal error: ... PCI: slot 1 function 0 not available for pcie-root-port, in use by ivshmem-plain``"

   -  Remember to add ``xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'``
      to the ``<domain>`` tag.

Running libvirt this way violates AppArmor and cgroups policies, which will
block the VM from running. These policies must be amended to allow the VM
to start.

.. tip::

   If you are not sure, you likely have cgroups also as this is usually deployed
   and configured by default by most distributions when you install libvirt.

AppArmor
^^^^^^^^

Create ``/etc/apparmor.d/local/abstractions/libvirt-qemu`` if it doesn't exist
and add the following:

.. code:: text

   # Looking Glass
   /dev/kvmfr0 rw,

cgroups
^^^^^^^

Edit the file ``/etc/libvirt/qemu.conf`` and uncomment the ``cgroup_device_acl``
block, adding ``/dev/kvmfr0`` to the list. To make this change active you then
must restart ``libvirtd``

.. code:: bash

   sudo systemctl restart libvirtd.service

.. _ivshmem_kvmfr_qemu:

QEMU
~~~~

If you are using QEMU directly without libvirt, add the following arguments to your
``qemu`` command line::

   -device ivshmem-plain,id=shmem0,memdev=looking-glass
   -object memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=32M,share=yes

.. note::

   The ``size`` argument must be the same size you passed
   to the ``static_size_mb`` argument when loading the kernel module.