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

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Date:   Tue, 3 Jul 2018 09:46:54 +0200
From:   Harald Freudenberger <freude@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP
 virtualization

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@...ux.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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