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256 lines
6.3 KiB
ReStructuredText
256 lines
6.3 KiB
ReStructuredText
.. _kernel_module:
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Kernel Module
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#############
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This kernel module implements a basic interface to the IVSHMEM device
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for Looking Glass in VM->VM mode.
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Additionally in VM->host mode, it can be used to generate a shared
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memory device on the host machine that supports dmabuf.
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Prerequisites
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-------------
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The linux kernel headers for your kernel version are required for building.
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Install them with ``apt-get``
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.. code:: bash
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apt-get install linux-headers-$(uname -r)
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Then switch to the ``module/`` directory
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.. code:: bash
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cd module/
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.. _module_dkms:
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Using DKMS (Recommended)
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------------------------
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You can use the kernel's DKMS feature to keep the module across upgrades.
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``dkms`` must be installed.
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.. code:: bash
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apt-get install dkms
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.. _module_dkms_install:
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Installing
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~~~~~~~~~~
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To install the module into DKMS, run
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.. code:: bash
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dkms install "."
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.. _module_dkms_loading:
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Loading
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~~~~~~~
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For VM->VM, simply modprobe the module::
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modprobe kvmfr
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For VM->host with dmabuf, modprobe with the parameter
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``static_size_mb``:
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.. code:: bash
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modprobe kvmfr static_size_mb=32
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Just like above, multiple devices can be created by separating the sizes
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with commas.
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.. _module_manual:
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Compiling & Loading (Manual)
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----------------------------
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To compile the module manually, run ``make`` in the module directory.
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.. _module_manual_loading:
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Loading
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~~~~~~~
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For VM->VM mode, run:
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.. code:: bash
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insmod kvmfr.ko
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For VM->host mode with dmabuf, instead of creating a shared memory file,
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load this module with the parameter ``static_size_mb``. For example, a
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32 MB shared memory device can be created with:
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.. code:: bash
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insmod kvmfr.ko static_size_mb=32
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Multiple devices can be created by separating the sizes with commas. For
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example, ``static_size_mb=128,64`` would create two kvmfr devices:
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``kvmfr0`` would be 128 MB and ``kvmfr1`` would be 64 MB.
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.. note::
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If you have already loaded an older version of the module, unload it
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first. You can do this by rebooting, or with ``rmmod``:
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.. code:: bash
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rmmod kvmfr.ko
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.. _module_usage:
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Usage
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-----
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The module will create the ``/dev/kvmfr0`` node, which represents the KVMFR
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interface. To use the interface, you need permission to access it by
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either: creating a udev rule to ensure your user can read and write to
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it, or simply change its ownership manually, i.e.:
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.. code:: bash
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sudo chown user:user /dev/kvmfr0
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As an example, you can create a new file in ``/etc/udev/rules.d/99-kvmfr.rules``
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with the following contents::
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SUBSYSTEM=="kvmfr", OWNER="user", GROUP="kvm", MODE="0660"
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(replace ``user`` with your username)
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Usage with Looking Glass is simple, you only need to specify the path to
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the device node, for example:
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.. code:: bash
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./looking-glass-client -f /dev/kvmfr0
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You may also use a config file: ``~/.looking-glass-client.ini``, or
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``/etc/looking-glass-client.ini``.
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.. code:: ini
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[app]
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shmFile=/dev/kvmfr0
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.. _module_vm_to_host:
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VM->Host
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~~~~~~~~
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In VM->host mode, use this device in place of the shared memory file.
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QEMU
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^^^^
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Add the following arguments to your ``qemu`` command line::
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-device ivshmem-plain,id=shmem0,memdev=looking-glass
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-object memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=32M,share=yes
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.. note::
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The ``size`` argument must be the same size you passed
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to the ``static_size_mb`` argument when loading the kernel module.
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libvirt
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^^^^^^^
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Starting with QEMU 6.2 and libvirt 7.9, JSON style QEMU configuration is the
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default syntax. Users running QEMU 6.2 or later **and** libvirt 7.9 or later,
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should use this XML block to configure their VM for kvmfr:
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.. code:: xml
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<qemu:commandline>
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<qemu:arg value='-device'/>
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<qemu:arg value='{"driver":"ivshmem-plain","id":"shmem0","memdev":"looking-glass"}'/>
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<qemu:arg value='-object'/>
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<qemu:arg value='{"qom-type":"memory-backend-file","id":"looking-glass","mem-path":"/dev/kvmfr0","size":33554432,"share":true}'/>
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</qemu:commandline>
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.. note::
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- Using an incorrect syntax for your host configuration may cause QEMU to
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abort with the following error message:
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"``error: internal error: ... PCI: slot 1 function 0 not available for pcie-root-port, in use by ivshmem-plain``"
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- The ``"size"`` tag represents the size of the shared memory device in
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bytes. Once you determine the proper size of the device as per
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:ref:`Determining Memory <client_determining_memory>`, use the figure you
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got to calculate the size in bytes:
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``size_in_MB x 1024 x 1024 = size_in_bytes``
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If you are running QEMU older than 6.2 or libvirt older than 7.9, please use
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legacy syntax for IVSHMEM setup:
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.. code:: xml
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<qemu:commandline>
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<qemu:arg value='-device'/>
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<qemu:arg value='ivshmem-plain,id=shmem0,memdev=looking-glass'/>
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<qemu:arg value='-object'/>
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<qemu:arg value='memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=32M,share=yes'/>
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</qemu:commandline>
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.. note::
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Remember to add ``xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'``
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to the ``<domain>`` tag.
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Running libvirt this way violates AppArmor and cgroups policies, which will
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block the VM from running. These policies must be amended to allow the VM
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to start:
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- For AppArmor, create ``/etc/apparmor.d/local/abstractions/libvirt-qemu`` if
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it doesn't exist, and add the following::
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# Looking Glass
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/dev/kvmfr0 rw,
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- For cgroups, edit ``/etc/libvirt/qemu.conf``, uncomment the
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``cgroup_device_acl`` block, and add ``/dev/kvmfr0`` to the list.
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Then restart ``libvirtd``:
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.. code:: bash
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sudo systemctl restart libvirtd.service
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.. _systemd_modules_load:
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systemd-modules-load
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~~~~~~~~~~~~~~~~~~~~
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For convenience, you may load the KVMFR module when starting your computer.
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We can use the ``systemd-modules-load.service(8)`` service for this task.
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Create the file ``/etc/modules-load.d/kvmfr.conf`` with the following
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contents::
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#KVMFR Looking Glass module
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kvmfr
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This will now run the next time you start your machine.
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If you are running in VM->host mode, you must additionally create another file
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``/etc/modprobe.d/kvmfr.conf`` to properly set the size. It should have the
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following contents::
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#KVMFR Looking Glass module
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options kvmfr static_size_mb=32
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.. note::
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Don't forget to adjust ``static_size_mb`` to your needs.
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