| 1 | Subchannel passthrough via vfio-ccw |
| 2 | =================================== |
| 3 | |
| 4 | vfio-ccw (based upon the mediated vfio device infrastructure) allows to |
| 5 | make certain I/O subchannels and their devices available to a guest. The |
| 6 | host will not interact with those subchannels/devices any more. |
| 7 | |
| 8 | Note that while vfio-ccw should work with most non-QDIO devices, only ECKD |
| 9 | DASDs have really been tested. |
| 10 | |
| 11 | Example configuration |
| 12 | --------------------- |
| 13 | |
| 14 | Step 1: configure the host device |
| 15 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 16 | |
| 17 | As 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 | |
| 22 | Note: it is recommended to use the ``mdevctl`` tool for actually configuring |
| 23 | the host device. |
| 24 | |
| 25 | To define the same device as configured below to be started |
| 26 | automatically, 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 | |
| 34 | If using ``mdevctl`` is not possible or wanted, follow the manual procedure |
| 35 | below. |
| 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 | |
| 53 | Step 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 |