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    SubjectRe: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization
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    On 02.07.2018 18:28, Halil Pasic wrote:
    >
    >
    > 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?
    What do you mean on this level with 'in use'? A unbind destroys the association
    between device and driver. There is no awareness of 'in use' or 'not in use' on this
    level. This is a hard 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
    >> +
    > [..]
    >
    > --
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