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