Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization

Halil Pasic
2018-07-02T16:28:42Z

On 06/29/2018 11:11 PM, Tony Krowiak wrote:
> This patch provides documentation describing the AP architecture and
> design concepts behind the virtualization of AP devices. It also
> includes an example of how to configure AP devices for exclusive
> use of KVM guests.
>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
[..]
> +
> +Reserve APQNs for exclusive use of KVM guests
> +---------------------------------------------
> +The following block diagram illustrates the mechanism by which APQNs are
> +reserved:
> +
> + +------------------+
> + remove | | unbind
> + +------------------->+ cex4queue driver +<-----------+
> + | | | |
> + | +------------------+ |
> + | |
> + | |
> + | |
> ++--------+---------+ register +------------------+ +-----+------+
> +| +<---------+ | bind | |
> +| ap_bus | | vfio_ap driver +<-----+ admin |
> +| +--------->+ | | |
> ++------------------+ probe +---+--------+-----+ +------------+
> + | |
> + create | | store APQN
> + | |
> + v v
> + +---+--------+-----+
> + | |
> + | matrix device |
> + | |
> + +------------------+
> +
> +The process for reserving an AP queue for use by a KVM guest is:
> +
> +* The vfio-ap driver during its initialization will perform the following:
> + * Create the 'vfio_ap' root device - /sys/devices/vfio_ap
> + * Create the 'matrix' device in the 'vfio_ap' root
> + * Register the matrix device with the device core
> +* Register with the ap_bus for AP queue devices of type 10 devices (CEX4 and
> + newer) and to provide the vfio_ap driver's probe and remove callback
> + interfaces. The reason why older devices are not supported is because there
> + are no systems available on which to test.
> +* The admin unbinds queue cc.qqqq from the cex4queue device driver. This results
> + in the ap_bus calling the the device driver's remove interface which
> + unbinds the cc.qqqq queue device from the driver.

What if the queue cc.qqqq is already in use? AFAIU unbind is almost as radical as
pulling a cable. What is the proper procedure an admin should follow before doing
the unbind?

> +* The admin binds the cc.qqqq queue to the vfio_ap device driver. This results
> + in the ap_bus calling the device vfio_ap driver's probe interface to bind
> + queue cc.qqqq to the driver. The vfio_ap device driver will store the APQN for
> + the queue in the matrix device
> +
[..]