Re: [PATCH v4 15/15] s390: doc: detailed specifications for AP virtualization

From: Tony Krowiak
Date: Tue Apr 17 2018 - 12:15:04 EST

On 04/16/2018 09:13 AM, Pierre Morel wrote:
On 15/04/2018 23:22, 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@xxxxxxxxxxxxxxxxxx>
---
Documentation/s390/vfio-ap.txt | 567 ++++++++++++++++++++++++++++++++++++++++
MAINTAINERS | 1 +
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+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 CEX4, CEX5 and
+ CEX6 and to provide the vfio_ap driver's probe and remove callback interfaces.

I wonder why the type of card has anything to do with this driver.
It should be transparent, the driver should be able to provide the matrix (APM/AQM/ADM)
independently from the type of card in the slot.

We've been down this road several times before. We are only supporting virtualization of
CEX4 and newer cards. Also, the AP bus requires registering for specific card types.



Regards,

Pierre