Message-Id: <1530306683-7270-22-git-send-email-akrowiak@linux.vnet.ibm.com>
Date:   Fri, 29 Jun 2018 17:11:23 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     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,
        akrowiak@...ux.vnet.ibm.com, Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization

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>
---
 Documentation/s390/vfio-ap.txt |  575 ++++++++++++++++++++++++++++++++++++++++
 MAINTAINERS                    |    1 +
 2 files changed, 576 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/s390/vfio-ap.txt

diff --git a/Documentation/s390/vfio-ap.txt b/Documentation/s390/vfio-ap.txt
new file mode 100644
index 0000000..79f3d43
--- /dev/null
+++ b/Documentation/s390/vfio-ap.txt
@@ -0,0 +1,575 @@
+Introduction:
+============
+The Adjunct Processor (AP) facility is an IBM Z cryptographic facility comprised
+of three AP instructions and from 1 up to 256 PCIe cryptographic adapter cards.
+The AP devices provide cryptographic functions to all CPUs assigned to a
+linux system running in an IBM Z system LPAR.
+
+The AP adapter cards are exposed via the AP bus. The motivation for vfio-ap
+is to make AP cards available to KVM guests using the VFIO mediated device
+framework. This implementation relies considerably on the s390 virtualization
+facilities which do most of the hard work of providing direct access to AP
+devices.
+
+AP Architectural Overview:
+=========================
+To facilitate the comprehension of the design, let's start with some
+definitions:
+
+* AP adapter
+
+  An AP adapter is an IBM Z adapter card that can perform cryptographic
+  functions. There can be from 0 to 256 adapters assigned to an LPAR. Adapters
+  assigned to the LPAR in which a linux host is running will be available to
+  the linux host. Each adapter is identified by a number from 0 to 255. When
+  installed, an AP adapter is accessed by AP instructions executed by any CPU.
+
+  The AP adapter cards are assigned to a given LPAR via the system's Activation
+  Profile which can be edited via the HMC. When the system is IPL'd, the AP bus
+  module is loaded and detects the AP adapter cards assigned to the LPAR. The AP
+  bus creates a sysfs device for each adapter as they are detected. For example,
+  if AP adapters 4 and 10 (0x0a) are assigned to the LPAR, the AP bus will
+  create the following sysfs entries:
+
+    /sys/devices/ap/card04
+    /sys/devices/ap/card0a
+
+  Symbolic links to these devices will also be created in the AP bus devices
+  sub-directory:
+
+    /sys/bus/ap/devices/[card04]
+    /sys/bus/ap/devices/[card04]
+
+* AP domain
+
+  An adapter is partitioned into domains. Each domain can be thought of as
+  a set of hardware registers for processing AP instructions. An adapter can
+  hold up to 256 domains. Each domain is identified by a number from 0 to 255.
+  Domains can be further classified into two types:
+
+    * Usage domains are domains that can be accessed directly to process AP
+      commands.
+
+    * Control domains are domains that are accessed indirectly by AP
+      commands sent to a usage domain to control or change the domain, for
+      example; to set a secure private key for the domain.
+
+  The AP usage and control domains are assigned to a given LPAR via the system's
+  Activation Profile which can be edited via the HMC. When the system is IPL'd,
+  the AP bus module is loaded and detects the AP usage and control domains
+  assigned to the LPAR. The domain number of each usage domain will be coupled
+  with the adapter number of each AP adapter assigned to the LPAR to identify
+  the AP queues (see AP Queue section below). The domain number of each control
+  domain will be represented in a bitmask and stored in a sysfs file
+  /sys/bus/ap/ap_control_domain_mask created by the bus. The bits in the mask,
+  from most to least significant bit, correspond to domains 0-255.
+
+  A domain may be assigned to a system as both a usage and control domain, or
+  as a control domain only. Consequently, all domains assigned as both a usage
+  and control domain can both process AP commands as well as be changed by an AP
+  command sent to any usage domain assigned to the same system. Domains assigned
+  only as control domains can not process AP commands but can be changed by AP
+  commands sent to any usage domain assigned to the system.
+
+* AP Queue
+
+  An AP queue is the means by which an AP command-request message is sent to a
+  usage domain inside a specific adapter. An AP queue is identified by a tuple
+  comprised of an AP adapter ID (APID) and an AP queue index (APQI). The
+  APQI corresponds to a given usage domain number within the adapter. This tuple
+  forms an AP Queue Number (APQN) uniquely identifying an AP queue. AP
+  instructions include a field containing the APQN to identify the AP queue to
+  which the AP command-request message is to be sent for processing.
+
+  The AP bus will create a sysfs device for each APQN that can be derived from
+  the intersection of the AP adapter and usage domain numbers detected when the
+  AP bus module is loaded. For example, if adapters 4 and 10 (0x0a) and usage
+  domains 6 and 71 (0x47) are assigned to the LPAR, the AP bus will create the
+  following sysfs entries:
+
+    /sys/devices/ap/card04/04.0006
+    /sys/devices/ap/card04/04.0047
+    /sys/devices/ap/card0a/0a.0006
+    /sys/devices/ap/card0a/0a.0047
+
+  The following symbolic links to these devices will be created in the AP bus
+  devices subdirectory:
+
+    /sys/bus/ap/devices/[04.0006]
+    /sys/bus/ap/devices/[04.0047]
+    /sys/bus/ap/devices/[0a.0006]
+    /sys/bus/ap/devices/[0a.0047]
+
+* AP Instructions:
+
+  There are three AP instructions:
+
+  * NQAP: to enqueue an AP command-request message to a queue
+  * DQAP: to dequeue an AP command-reply message from a queue
+  * PQAP: to administer the queues
+
+AP and SIE:
+==========
+Let's now see how AP instructions are interpreted by the hardware.
+
+A satellite control block called the Crypto Control Block is attached to our
+main hardware virtualization control block. The CRYCB contains three fields to
+identify the adapters, usage domains and control domains assigned to the KVM
+guest:
+
+* The AP Mask (APM) field is a bit mask that identifies the AP adapters assigned
+  to the KVM guest. Each bit in the mask, from most significant to least
+  significant bit, corresponds to an APID from 0-255. If a bit is set, the
+  corresponding adapter is valid for use by the KVM guest.
+
+* The AP Queue Mask (AQM) field is a bit mask identifying the AP usage domains
+  assigned to the KVM guest. Each bit in the mask, from most significant to
+  least significant bit, corresponds to an AP queue index (APQI) from 0-255. If
+  a bit is set, the corresponding queue is valid for use by the KVM guest.
+
+* The AP Domain Mask field is a bit mask that identifies the AP control domains
+  assigned to the KVM guest. The ADM bit mask controls which domains can be
+  changed by an AP command-request message sent to a usage domain from the
+  guest. Each bit in the mask, from least significant to most significant bit,
+  corresponds to a domain from 0-255. If a bit is set, the corresponding domain
+  can be modified by an AP command-request message sent to a usage domain
+  configured for the KVM guest.
+
+If you recall from the description of an AP Queue, AP instructions include
+an APQN to identify the AP adapter and AP queue to which an AP command-request
+message is to be sent (NQAP and PQAP instructions), or from which a
+command-reply message is to be received (DQAP instruction). The validity of an
+APQN is defined by the matrix calculated from the APM and AQM; it is the
+cross product of all assigned adapter numbers (APM) with all assigned queue
+indexes (AQM). For example, if adapters 1 and 2 and usage domains 5 and 6 are
+assigned to a guest, the APQNs (1,5), (1,6), (2,5) and (2,6) will be valid for
+the guest.
+
+The APQNs can provide secure key functionality - i.e., a private key is stored
+on the adapter card for each of its domains - so each APQN must be assigned to
+at most one guest or the linux host.
+
+   Example 1: Valid configuration:
+   ------------------------------
+   Guest1: adapters 1,2  domains 5,6
+   Guest2: adapter  1,2  domain 7
+
+   This is valid because both guests have a unique set of APQNs: Guest1 has
+   APQNs (1,5), (1,6), (2,5) and (2,6); Guest2 has APQNs (1,7) and (2,7).
+
+   Example 2: Invalid configuration:
+   --------------------------------is assigned by writing the adapter's number into the
+   Guest1: adapters 1,2  domains 5,6
+   Guest2: adapter  1    domains 6,7
+
+   This is an invalid configuration because both guests have access to
+   APQN (1,6).
+
+The Design:
+===========
+The design introduces three new objects:
+
+1. AP matrix device
+2. VFIO AP device driver (vfio_ap.ko)
+3. AP mediated matrix passthrough device
+
+The VFIO AP device driver
+-------------------------
+The VFIO AP (vfio_ap) device driver serves the following purposes:
+
+1. Provides the interfaces to reserve APQNs for exclusive use of KVM guests.
+
+2. Sets up the VFIO mediated device interfaces to manage the mediated matrix
+   device and create the sysfs interfaces for assigning adapters, usage domains,
+   and control domains comprising the matrix for a KVM guest.
+
+3. Configure the APM, AQM and ADM in the CRYCB referenced by a KVM guest's
+   SIE state description to grant the guest access to AP devices
+
+4. Initialize the CPU model feature indicating that a KVM guest may use
+   AP facilities installed on the linux host.
+
+5. Enable interpretive execution mode for the KVM guest.
+
+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.
+* 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
+
+Set up the VFIO mediated device interfaces
+------------------------------------------
+The VFIO AP device driver utilizes the common interface of the VFIO mediated
+device core driver to:
+* Register an AP mediated bus driver to add a mediated matrix device to and
+  remove it from a VFIO group.
+* Create and destroy a mediated matrix device
+* Add a mediated matrix device to and remove it from the AP mediated bus driver
+* Add a mediated matrix device to and remove it from an IOMMU group
+
+The following high-level block diagram shows the main components and interfaces
+of the VFIO AP mediated matrix device driver:
+
+ +-------------+
+ |             |
+ | +---------+ | mdev_register_driver() +--------------+
+ | |  Mdev   | +<-----------------------+              |
+ | |  bus    | |                        | vfio_mdev.ko |
+ | | driver  | +----------------------->+              |<-> VFIO user
+ | +---------+ |    probe()/remove()    +--------------+    APIs
+ |             |
+ |  MDEV CORE  |
+ |   MODULE    |
+ |   mdev.ko   |
+ | +---------+ | mdev_register_device() +--------------+
+ | |Physical | +<-----------------------+              |
+ | | device  | |                        |  vfio_ap.ko  |<-> matrix
+ | |interface| +----------------------->+              |    device
+ | +---------+ |       callback         +--------------+
+ +-------------+
+
+During initialization of the vfio_ap module, the matrix device is registered
+with an 'mdev_parent_ops' structure that provides the sysfs attribute
+structures, mdev functions and callback interfaces for managing the mediated
+matrix device.
+
+* sysfs attribute structures:
+  * supported_type_groups
+    The VFIO mediated device framework supports creation of user-defined
+    mediated device types. These mediated device types are specified
+    via the 'supported_type_groups' structure when a device is registered
+    with the mediated device framework. The registration process creates the
+    sysfs structures for each mediated device type specified in the
+    'mdev_supported_types' sub-directory of the device being registered. Along
+    with the device type, the sysfs attributes of the mediated device type are
+    provided.
+
+    The VFIO AP device driver will register one mediated device type for
+    passthrough devices:
+        /sys/devices/vfio_ap/mdev_supported_types/vfio_ap-passthrough
+    Only the three read-only attributes required by the VFIO mdev framework will
+    be provided:
+        /sys/devices/vfio_ap/mdev_supported_types
+        ... name
+        ... device_api
+        ... available_instances
+        Where:
+        * name: specifies the name of the mediated device type
+        * device_api: the mediated device type's API
+        * available_instances: the number of mediated matrix passthrough devices
+                               that can be created
+  * mdev_attr_groups
+    This attribute group identifies the user-defined sysfs attributes of the
+    mediated device. When a device is registered with the VFIO mediated device
+    framework, the sysfs attributes files identified in the 'mdev_attr_groups'
+    structure will be created in the mediated matrix device's directory. The
+    sysfs attributes for a mediated matrix device are:
+    * assign_adapter:
+      A write-only file for assigning an AP adapter to the mediated matrix
+      device. To assign an adapter, the APID of the adapter is written to the
+      file.
+    * assign_domain:
+      A write-only file for assigning an AP usage domain to the mediated matrix
+      device. To assign a domain, the APQI of the AP queue corresponding to a
+      usage domain is written to the file.
+    * matrix:
+      A read-only file for displaying the APQNs derived from the adapters and
+      domains assigned to the mediated matrix device.
+    * assign_control_domain:
+      A write-only file for assigning an AP control domain to the mediated
+      matrix device. To assign a control domain, the ID of a domain to be
+      controlled is written to the file. For the initial implementation, the set
+      of control domains will always include the set of usage domains, so it is
+      only necessary to assign control domains that are not also assigned as
+      usage domains.
+    * control_domains:
+      A read-only file for displaying the control domain numbers assigned to the
+      mediated matrix device.
+
+* functions:
+  * create:
+    allocates the ap_matrix_mdev structure used by the vfio_ap driver to:
+    * Keep track of the available instances
+    * Store the reference to the struct kvm for the KVM guest
+    * Provide the notifier callback that will get invoked to handle the
+      VFIO_GROUP_NOTIFY_SET_KVM event. When received, the vfio_ap driver will
+      store the reference in the mediated matrix device's ap_matrix_mdev
+      structure and enable the interpretive execution mode for the KVM guest.
+  * remove:
+    deallocates the mediated matrix device's ap_matrix_mdev structure.
+
+* callback interfaces
+  * open:
+    The vfio_ap driver uses this callback to register a
+    VFIO_GROUP_NOTIFY_SET_KVM notifier callback function for the mdev matrix
+    device. The notifier is invoked when QEMU connects the VFIO iommu group
+    for the mdev matrix device to the MDEV bus. Access to the KVM structure used
+    to configure the KVM guest is provided via this callback. The KVM structure,
+    is used to configure the guest's access to the AP matrix defined via the
+    mediated matrix device's sysfs attribute files.
+  * release:
+    unregisters the VFIO_GROUP_NOTIFY_SET_KVM notifier callback function for the
+    mdev matrix device and deconfigures the guest's AP matrix.
+
+Configure the APM, AQM and ADM in the CRYCB:
+-------------------------------------------
+Configuring the AP matrix for a KVM guest will be performed when the
+VFIO_GROUP_NOTIFY_SET_KVM notifier callback is invoked. The notifier
+function is called when QEMU connects the VFIO iommu group for the mdev matrix
+device to the MDEV bus. The CRYCB is configured by:
+* Setting the bits in the APM corresponding to the APIDs assigned to the
+  mediated matrix device via its 'assign_adapter' interface.
+* Setting the bits in the AQM corresponding to the APQIs assigned to the
+  mediated matrix device via its 'assign_domain' interface.
+* Setting the bits in the ADM corresponding to the domain dIDs assigned to the
+  mediated matrix device via its 'assign_control_domains' interface.
+
+Initialize the CPU model feature for AP
+---------------------------------------
+A new CPU model feature, KVM_S390_VM_CPU_FEAT_AP, is introduced to indicate that
+AP instructions are available to the KVM guest. This feature will be enabled by
+KVM only if the AP instructions are installed on the linux host. The feature
+must be turned on for the guest in order to access AP devices from the guest.
+For example, to turn the AP facilities on from the QEMU command line:
+
+    /usr/bin/qemu-system-s390x ... -cpu xxx,ap=on
+
+    Where xxx is the CPU model being used.
+
+    If the CPU model feature is not enabled by the kernel, QEMU will fail and
+    report that the feature is not supported.
+
+Example:
+=======
+Let's now provide an example to illustrate how KVM guests may be given
+access to AP facilities. For this example, we will show how to configure
+two guests such that executing the lszcrypt command on the guests would
+look like this:
+
+Guest1
+------
+CARD.DOMAIN TYPE  MODE
+------------------------------
+05          CEX5C CCA-Coproc
+05.0004     CEX5C CCA-Coproc
+05.00ab     CEX5C CCA-Coproc
+06          CEX5A Accelerator
+06.0004     CEX5A Accelerator
+06.00ab     CEX5C CCA-Coproc
+
+Guest2
+------
+CARD.DOMAIN TYPE  MODE
+------------------------------
+05          CEX5A Accelerator
+05.0047     CEX5A Accelerator
+05.00ff     CEX5A Accelerator
+
+These are the steps:
+
+1. Install the vfio_ap module on the linux host. The dependency chain for the
+   vfio_ap module is:
+   * vfio
+   * mdev
+   * vfio_mdev
+   * KVM
+   * vfio_ap
+
+2. Secure the AP queues to be used by the two guests so that the host can not
+   access them. Only type 10 adapters (i.e., CEX4 and later) are supported
+   due to the fact that no test systems with older card types are available
+   for testing.
+
+   To secure the AP queues each, each AP Queue device must first be unbound from
+   the cex4queue device driver. The sysfs location of the driver is:
+
+   /sys/bus/ap
+   --- [drivers]
+   ------ [cex4queue]
+   --------- [05.0004]
+   --------- [05.0047]
+   --------- [05.00ab]
+   --------- [05.00ff]
+   --------- [06.0004]
+   --------- [06.00ab]
+   --------- unbind
+
+   To unbind AP queue 05.0004 from the cex4queue device driver:
+
+	echo 05.0004 > unbind
+
+   This must also be done for AP queues 05.00ab, 05.0047, 05.00ff, 06.0004,
+   and 06.00ab.
+
+   The AP Queues that were unbound must then be reserves for use by the two KVM
+   guests. This is accomplished by binding them to the vfio_ap device driver.
+   The sysfs location of the driver is:
+
+   /sys/bus/ap
+   ---[drivers]
+   ------ [vfio_ap]
+   ---------- bind
+
+   To bind queue 05.0004 to the vfio_ap driver:
+
+	echo 05.0004 > bind
+
+   This must also be done for AP queues 05.00ab, 05.0047, 05.00ff, 06.0004,
+   and 06.00ab.
+
+   Take note that the AP queues bound to the vfio_ap driver will be available
+   for guest usage until they are unbound from the driver, the vfio_ap module
+   is unloaded, or the host system is shut down.
+
+3. Create the mediated devices needed to configure the AP matrixes for the
+   two guests and to provide an interface to the vfio_ap driver for
+   use by the guests:
+
+   /sys/devices/
+   --- [vfio_ap]
+   ------ [matrix] (this is the matrix device)
+   --------- [mdev_supported_types]
+   ------------ [vfio_ap-passthrough] (passthrough mediated matrix device type)
+   --------------- create
+   --------------- [devices]
+
+   To create the mediated devices for the two guests:
+
+	uuidgen > create
+	uuidgen > create
+
+   This will create two mediated devices in the [devices] subdirectory named
+   with the UUID written to the create attribute file. We call them $uuid1
+   and $uuid2:
+
+   /sys/devices/
+   --- [vfio_ap]
+   ------ [matrix]
+   --------- [mdev_supported_types]
+   ------------ [vfio_ap-passthrough]
+   --------------- [devices]
+   ------------------ [$uuid1]
+   --------------------- assign_adapter
+   --------------------- assign_control_domain
+   --------------------- assign_domain
+   --------------------- matrix
+   --------------------- unassign_adapter
+   --------------------- unassign_control_domain
+   --------------------- unassign_domain
+
+   ------------------ [$uuid2]
+   --------------------- assign_adapter
+   --------------------- assign_cTo assign an adapter, the APID of the adapter is written to the
+      file. ontrol_domain
+   --------------------- assign_domain
+   --------------------- matrix
+   --------------------- unassign_adapter
+   --------------------- unassign_control_domain
+   --------------------- unassign_domain
+
+4. The administrator now needs to configure the matrixes for mediated
+   devices $uuid1 (for Guest1) and $uuid2 (for Guest2).
+
+   This is how the matrix is configured for Guest1:
+
+   echo 5 > assign_adapter
+   echo 6 > assign_adapter
+   echo 4 > assign_domain
+   echo 0xab > assign_domain
+
+   For this implementation, all usage domains - i.e., domains assigned
+   via the assign_domain attribute file - will also be configured in the ADM
+   field of the KVM guest's CRYCB, so there is no need to assign control
+   domains here unless you want to assign control domains that are not
+   assigned as usage domains.
+
+   If a mistake is made configuring an adapter, domain or control domain,
+   you can use the unassign_xxx files to unassign the adapter, domain or
+   control domain.
+
+   To display the matrix configuration for Guest1:
+
+   cat matrix
+
+   This is how the matrix is configured for Guest2:
+
+   echo 5 > assign_adapter
+   echo 0x47 > assign_domain
+   echo 0xff > assign_domain
+
+6. Start Guest1:
+
+   /usr/bin/qemu-system-s390x ... -cpu xxx,ap=on \
+      -device vfio-ap,sysfsdev=/sys/devices/vfio_ap/matrix/$uuid1 ...
+
+7. Start Guest2:
+
+   /usr/bin/qemu-system-s390x ... -cpu xxx,ap=on \
+      -device vfio-ap,sysfsdev=/sys/devices/vfio_ap/matrix/$uuid2 ...
+
+When the guest is shut down, the mediated matrix device may be removed.
+
+Using our example again, to remove the mediated matrix device $uuid1:
+
+   /sys/devices/
+      --- [vfio_ap]
+      ------ [matrix]
+      --------- [mdev_supported_types]
+      ------------ [vfio_ap-passthrough]
+      --------------- [devices]
+      ------------------ [$uuid1]
+      --------------------- remove
+
+   echo 1 > remove
+
+   This will remove all of the mdev matrix device's sysfs structures. To
+   recreate and reconfigure the mdev matrix device, all of the steps starting
+   with step 4 will have to be performed again.
+
+   It is not necessary to remove an mdev matrix device, but one may want to
+   remove it if no guest will use it during the lifetime of the linux host. If
+   the mdev matrix device is removed, one may want to unbind the AP queues the
+   guest was using from the vfio_ap device driver and bind them back to the
+   default driver. Alternatively, the AP queues can be configured for another
+   mdev matrix (i.e., guest). In either case, one must take care to change the
+   secure key configured for the domain to which the queue is connected.
\ No newline at end of file
diff --git a/MAINTAINERS b/MAINTAINERS
index 3217803..c693a23 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12411,6 +12411,7 @@ S:	Supported
 F:	drivers/s390/crypto/vfio_ap_drv.c
 F:	drivers/s390/crypto/vfio_ap_private.h
 F:	drivers/s390/crypto/vfio_ap_ops.c
+F:	Documentation/s390/vfio-ap.txt
 
 S390 ZFCP DRIVER
 M:	Steffen Maier <maier@...ux.ibm.com>
-- 
1.7.1

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