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Subchannel passthrough via vfio-ccw
===================================
vfio-ccw (based upon the mediated vfio device infrastructure) allows to
make certain I/O subchannels and their devices available to a guest. The
host will not interact with those subchannels/devices any more.
Note that while vfio-ccw should work with most non-QDIO devices, only ECKD
DASDs have really been tested.
Example configuration
---------------------
Step 1: configure the host device
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As every mdev is identified by a uuid, the first step is to obtain one::
[root@host ~]# uuidgen
7e270a25-e163-4922-af60-757fc8ed48c6
Note: it is recommended to use the ``mdevctl`` tool for actually configuring
the host device.
To define the same device as configured below to be started
automatically, use
::
[root@host ~]# driverctl -b css set-override 0.0.0313 vfio_ccw
[root@host ~]# mdevctl define -u 7e270a25-e163-4922-af60-757fc8ed48c6 \
-p 0.0.0313 -t vfio-ccw_io -a
If using ``mdevctl`` is not possible or wanted, follow the manual procedure
below.
* Locate the subchannel for the device (in this example, ``0.0.2b09``)::
[root@host ~]# lscss | grep 0.0.2b09 | awk '{print $2}'
0.0.0313
* Unbind the subchannel (in this example, ``0.0.0313``) from the standard
I/O subchannel driver and bind it to the vfio-ccw driver::
[root@host ~]# echo 0.0.0313 > /sys/bus/css/devices/0.0.0313/driver/unbind
[root@host ~]# echo 0.0.0313 > /sys/bus/css/drivers/vfio_ccw/bind
* Create the mediated device (identified by the uuid)::
[root@host ~]# echo "7e270a25-e163-4922-af60-757fc8ed48c6" > \
/sys/bus/css/devices/0.0.0313/mdev_supported_types/vfio_ccw-io/create
Step 2: configure QEMU
~~~~~~~~~~~~~~~~~~~~~~
* Reference the created mediated device and (optionally) pick a device id to
be presented in the guest (here, ``fe.0.1234``, which will end up visible
in the guest as ``0.0.1234``::
-device vfio-ccw,devno=fe.0.1234,sysfsdev=\
/sys/bus/mdev/devices/7e270a25-e163-4922-af60-757fc8ed48c6
* Start the guest. The device (here, ``0.0.1234``) should now be usable::
[root@guest ~]# lscss -d 0.0.1234
Device Subchan. DevType CU Type Use PIM PAM POM CHPID
----------------------------------------------------------------------
0.0.1234 0.0.0007 3390/0e 3990/e9 f0 f0 ff 1a2a3a0a 00000000
[root@guest ~]# chccwdev -e 0.0.1234
Setting device 0.0.1234 online
Done
[root@guest ~]# dmesg -t
(...)
dasd-eckd 0.0.1234: A channel path to the device has become operational
dasd-eckd 0.0.1234: New DASD 3390/0E (CU 3990/01) with 10017 cylinders, 15 heads, 224 sectors
dasd-eckd 0.0.1234: DASD with 4 KB/block, 7212240 KB total size, 48 KB/track, compatible disk layout
dasda:VOL1/ 0X2B09: dasda1
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