Re: [PATCH v8 00/13] basic channel IO passthrough infrastructure based on vfio

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 17 May 2017 02:48:00 +0200
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

> The patch series introduce a basic channel I/O passthrough
> infrastructure based on vfio.
> - Focus on supporting dasd-eckd(cu_type/dev_type = 0x3990/0x3390) as
>   the target device. 
> - Support new qemu parameters in the style of:
>     -machine s390-ccw-virtio(,s390-squash-mcss=on|off) \
>     -device vfio-ccw,sysfsdev=$MDEV_PATH
>   We want to support real (i.e. not virtual) channel devices even for
>   guests that do not support MCSS-E (where guests may see devices from
>   any channel subsystem image at once). As all virtio-ccw devices are in
>   css 0xfe (and show up in the default css 0 for guests not activating
>   MCSS-E), we need an option to squash e.g. passed-through channel devices
>   from their real css (0-3, or 0 for hosts not activating MCSS-E) into
>   the default css, that is what the new machine option s390-squash-css is
>   added.

Patches queued, with minor changes (see my comments).

I'll push out to s390-next once this passes some of my tests.

> 
> Build and install:
> 1. kernel configuration
>   CONFIG_S390_CCW_IOMMU=m
>   CONFIG_VFIO=m
>   CONFIG_VFIO_MDEV=m
>   CONFIG_VFIO_MDEV_DEVICE=m
>   CONFIG_VFIO_CCW=m
> 2. modules required
>   modprobe vfio.ko
>   modprobe mdev.ko
>   modprobe vfio_mdev.ko
>   modprobe vfio_iommu_type1.ko
>   modprobe vfio_ccw.ko
> 3. find a subchannel(0.0."%schid") of a DASD-ECKD device and bind it to
>   vfio_ccw driver
>   #find the dasd you can use with lsdasd on your host. e.g.:
>   devno="7e52"
>   schid="16ca"
>   #unbind the ccw device from the subchannel
>   echo 0.0."$devno" > /sys/bus/ccw/devices/0.0."$devno"/driver/unbind
>   #unbind the subchannel from io_subchannel driver
>   echo 0.0."$schid" > /sys/bus/css/devices/0.0."$schid"/driver/unbind
>   #bind the subchannel with vfio_ccw driver
>   echo 0.0."$schid" > /sys/bus/css/drivers/vfio_ccw/bind
> 4. create a mediated device
>   #generate a uuid with uuidgen. e.g.:
>   uuid="6dfd3ec5-e8b3-4e18-a6fe-57bc9eceb920"
>   echo "$uuid" > \
>   /sys/bus/css/devices/0.0."$schid"/mdev_supported_types/vfio_ccw-io/create
> 5. pass-through this device to a vm
>   -M s390-ccw-virtio,s390-squash-css=on \
>   -device vfio-ccw,sysfsdev=/sys/bus/mdev/devices/$uuid \
>   ... ...

These instructions would be helpful to preserve in the qemu wiki and
could even be expanded upon. Ping me if you need an account (hint,
hint ;)