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Re: [libvirt] [RFC PATCH 00/16] Introduce vGPU mdev framework to libvirt



On Mon,  6 Feb 2017 13:19:42 +0100
Erik Skultety <eskultet redhat com> wrote:

> Finally. It's here. This is the initial suggestion on how libvirt might
> interract with the mdev framework, currently only focussing on the non-managed
> devices, i.e. those pre-created by the user, since that will be revisited once
> we all settled on how the XML should look like, given we might not want to use
> the sysfs path directly as an attribute in the domain XML. My proposal on the
> XML is the following:
> 
> <hostdev mode='subsystem' type='mdev'>  
>     <source>
>         <!-- this is the host's physical device address -->
>         <address domain='0x0000' bus='0x00' slot='0x00' function='0x00'>
>         <uuid>vGPU_UUID<uuid>
>     <source>
>     <!-- target PCI address can be omitted to assign it automatically -->
> </hostdev>
> 
> So the mediated device is identified by the physical parent device visible on
> the host and a UUID which allows us to construct the sysfs path by ourselves,
> which we then put on the QEMU's command line.

Based on your test code, I think you're creating something like this:

-device vfio-pci,sysfsdev=/sys/class/mdev_bus/0000:00:03.0/53764d0e-85a0-42b4-af5c-2046b460b1dc

That would explain the need for the parent device address, but that's
an entirely self inflicted requirement.  For a managed="no" scenarios,
we shouldn't need the parent, we can get to the mdev device
via /sys/bus/mdev/devices/53764d0e-85a0-42b4-af5c-2046b460b1dc.  So it
seems that the UUID should be the only required source element for
managed="no".

For managed="yes", it seems like the parent device is still an optional
field.  The most important thing that libvirt needs to know when
creating a mdev device for a VM is the mdev type name.  The parent
device should be an optional field to help higher level management
tools deal with placement of the device for locality or load balancing.
Also, we can't assume that the parent device is a PCI device, the
sample mtty driver already breaks this assumption.

Also, grep'ing through the patches, I don't see that the "device_api"
file is being used to test that the mdev device actually exports the
vfio-pci API before making use of it with the QEMU vfio-pci driver.  We
don't yet have any examples to the contrary, but non vfio-pci mdev
devices are in development.  Just like we can't assume the parent
device type, we can't assume the API of an mdev device to the user.
Thanks,

Alex

> A few remarks if you actually happen to have a machine to test this on:
> - right now the mediated devices are one-time use only, i.e. they have to be
> recreated before every machine boot
> - I wouldn't recommend assigning multiple vGPUs to a single domain
> 
> Once this series is sorted out, we can then continue with 'managed=yes' where
> as Laine pointed out [1], we need to figure out how exactly should the
> management layer hint libvirt which vGPU type should be used for device
> instantiation.
> 
> [1] https://www.redhat.com/archives/libvir-list/2017-January/msg00287.html  
> 
> #pleaseshareyourfeedback
> 
> Thanks,
> Erik
> 
> Erik Skultety (16):
>   util: Introduce new module virmdev
>   conf: Introduce new hostdev device type mdev
>   docs: Update RNG schema to reflect the new hostdev type mdev
>   conf: Adjust the domain parser to work with mdevs
>   Adjust the formatter to reflect the new hostdev type mdev
>   security: dac: Enable labeling of vfio mediated devices
>   security: selinux: Enable labeling of vfio mediated devices
>   conf: Enable cold-plug of a mediated device
>   qemu: Assign PCI addresses for mediated devices as well
>   hostdev: Maintain a driver list of active mediated devices
>   hostdev: Introduce a reattach method for mediated devices
>   qemu: cgroup: Adjust cgroups' logic to allow mediated devices
>   qemu: namespace: Hook up the discovery of mdevs into the namespace
>     code
>   qemu: Format mdevs on the qemu command line
>   test: Add some test cases for our test suite regarding the mdevs
>   docs: Document the new hostdev device type 'mdev'
> 
>  docs/formatdomain.html.in                          |  40 ++-
>  docs/schemas/domaincommon.rng                      |  17 +
>  po/POTFILES.in                                     |   1 +
>  src/Makefile.am                                    |   1 +
>  src/conf/domain_conf.c                             |  81 ++++-
>  src/conf/domain_conf.h                             |  10 +
>  src/libvirt_private.syms                           |  19 ++
>  src/qemu/qemu_cgroup.c                             |  35 ++
>  src/qemu/qemu_command.c                            |  49 +++
>  src/qemu/qemu_command.h                            |   5 +
>  src/qemu/qemu_domain.c                             |  13 +
>  src/qemu/qemu_domain_address.c                     |  12 +-
>  src/qemu/qemu_hostdev.c                            |  37 ++
>  src/qemu/qemu_hostdev.h                            |   8 +
>  src/qemu/qemu_hotplug.c                            |   2 +
>  src/security/security_apparmor.c                   |   3 +
>  src/security/security_dac.c                        |  56 +++
>  src/security/security_selinux.c                    |  55 +++
>  src/util/virhostdev.c                              | 179 +++++++++-
>  src/util/virhostdev.h                              |  16 +
>  src/util/virmdev.c                                 | 375 +++++++++++++++++++++
>  src/util/virmdev.h                                 |  85 +++++
>  tests/domaincapsschemadata/full.xml                |   1 +
>  ...qemuxml2argv-hostdev-mdev-unmanaged-no-uuid.xml |  37 ++
>  .../qemuxml2argv-hostdev-mdev-unmanaged.args       |  25 ++
>  .../qemuxml2argv-hostdev-mdev-unmanaged.xml        |  38 +++
>  tests/qemuxml2argvtest.c                           |   6 +
>  .../qemuxml2xmlout-hostdev-mdev-unmanaged.xml      |  41 +++
>  tests/qemuxml2xmltest.c                            |   1 +
>  29 files changed, 1239 insertions(+), 9 deletions(-)
>  create mode 100644 src/util/virmdev.c
>  create mode 100644 src/util/virmdev.h
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-hostdev-mdev-unmanaged-no-uuid.xml
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-hostdev-mdev-unmanaged.args
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-hostdev-mdev-unmanaged.xml
>  create mode 100644 tests/qemuxml2xmloutdata/qemuxml2xmlout-hostdev-mdev-unmanaged.xml
> 


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