1Subchannel passthrough via vfio-ccw 2=================================== 3 4vfio-ccw (based upon the mediated vfio device infrastructure) allows to 5make certain I/O subchannels and their devices available to a guest. The 6host will not interact with those subchannels/devices any more. 7 8Note that while vfio-ccw should work with most non-QDIO devices, only ECKD 9DASDs have really been tested. 10 11Example configuration 12--------------------- 13 14Step 1: configure the host device 15~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 16 17As every mdev is identified by a uuid, the first step is to obtain one:: 18 19 [root@host ~]# uuidgen 20 7e270a25-e163-4922-af60-757fc8ed48c6 21 22Note: it is recommended to use the ``mdevctl`` tool for actually configuring 23the host device. 24 25To define the same device as configured below to be started 26automatically, use 27 28:: 29 30 [root@host ~]# driverctl -b css set-override 0.0.0313 vfio_ccw 31 [root@host ~]# mdevctl define -u 7e270a25-e163-4922-af60-757fc8ed48c6 \ 32 -p 0.0.0313 -t vfio-ccw_io -a 33 34If using ``mdevctl`` is not possible or wanted, follow the manual procedure 35below. 36 37* Locate the subchannel for the device (in this example, ``0.0.2b09``):: 38 39 [root@host ~]# lscss | grep 0.0.2b09 | awk '{print $2}' 40 0.0.0313 41 42* Unbind the subchannel (in this example, ``0.0.0313``) from the standard 43 I/O subchannel driver and bind it to the vfio-ccw driver:: 44 45 [root@host ~]# echo 0.0.0313 > /sys/bus/css/devices/0.0.0313/driver/unbind 46 [root@host ~]# echo 0.0.0313 > /sys/bus/css/drivers/vfio_ccw/bind 47 48* Create the mediated device (identified by the uuid):: 49 50 [root@host ~]# echo "7e270a25-e163-4922-af60-757fc8ed48c6" > \ 51 /sys/bus/css/devices/0.0.0313/mdev_supported_types/vfio_ccw-io/create 52 53Step 2: configure QEMU 54~~~~~~~~~~~~~~~~~~~~~~ 55 56* Reference the created mediated device and (optionally) pick a device id to 57 be presented in the guest (here, ``fe.0.1234``, which will end up visible 58 in the guest as ``0.0.1234``:: 59 60 -device vfio-ccw,devno=fe.0.1234,sysfsdev=\ 61 /sys/bus/mdev/devices/7e270a25-e163-4922-af60-757fc8ed48c6 62 63* Start the guest. The device (here, ``0.0.1234``) should now be usable:: 64 65 [root@guest ~]# lscss -d 0.0.1234 66 Device Subchan. DevType CU Type Use PIM PAM POM CHPID 67 ---------------------------------------------------------------------- 68 0.0.1234 0.0.0007 3390/0e 3990/e9 f0 f0 ff 1a2a3a0a 00000000 69 [root@guest ~]# chccwdev -e 0.0.1234 70 Setting device 0.0.1234 online 71 Done 72 [root@guest ~]# dmesg -t 73 (...) 74 dasd-eckd 0.0.1234: A channel path to the device has become operational 75 dasd-eckd 0.0.1234: New DASD 3390/0E (CU 3990/01) with 10017 cylinders, 15 heads, 224 sectors 76 dasd-eckd 0.0.1234: DASD with 4 KB/block, 7212240 KB total size, 48 KB/track, compatible disk layout 77 dasda:VOL1/ 0X2B09: dasda1 78