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diff --git a/Documentation/misc-devices/ibmvmc.rst b/Documentation/misc-devices/ibmvmc.rst new file mode 100644 index 000000000..b46df4ea2 --- /dev/null +++ b/Documentation/misc-devices/ibmvmc.rst @@ -0,0 +1,227 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +====================================================== +IBM Virtual Management Channel Kernel Driver (IBMVMC) +====================================================== + +:Authors: + Dave Engebretsen <engebret@us.ibm.com>, + Adam Reznechek <adreznec@linux.vnet.ibm.com>, + Steven Royer <seroyer@linux.vnet.ibm.com>, + Bryant G. Ly <bryantly@linux.vnet.ibm.com>, + +Introduction +============ + +Note: Knowledge of virtualization technology is required to understand +this document. + +A good reference document would be: + +https://openpowerfoundation.org/wp-content/uploads/2016/05/LoPAPR_DRAFT_v11_24March2016_cmt1.pdf + +The Virtual Management Channel (VMC) is a logical device which provides an +interface between the hypervisor and a management partition. This interface +is like a message passing interface. This management partition is intended +to provide an alternative to systems that use a Hardware Management +Console (HMC) - based system management. + +The primary hardware management solution that is developed by IBM relies +on an appliance server named the Hardware Management Console (HMC), +packaged as an external tower or rack-mounted personal computer. In a +Power Systems environment, a single HMC can manage multiple POWER +processor-based systems. + +Management Application +---------------------- + +In the management partition, a management application exists which enables +a system administrator to configure the system’s partitioning +characteristics via a command line interface (CLI) or Representational +State Transfer Application (REST API's). + +The management application runs on a Linux logical partition on a +POWER8 or newer processor-based server that is virtualized by PowerVM. +System configuration, maintenance, and control functions which +traditionally require an HMC can be implemented in the management +application using a combination of HMC to hypervisor interfaces and +existing operating system methods. This tool provides a subset of the +functions implemented by the HMC and enables basic partition configuration. +The set of HMC to hypervisor messages supported by the management +application component are passed to the hypervisor over a VMC interface, +which is defined below. + +The VMC enables the management partition to provide basic partitioning +functions: + +- Logical Partitioning Configuration +- Start, and stop actions for individual partitions +- Display of partition status +- Management of virtual Ethernet +- Management of virtual Storage +- Basic system management + +Virtual Management Channel (VMC) +-------------------------------- + +A logical device, called the Virtual Management Channel (VMC), is defined +for communicating between the management application and the hypervisor. It +basically creates the pipes that enable virtualization management +software. This device is presented to a designated management partition as +a virtual device. + +This communication device uses Command/Response Queue (CRQ) and the +Remote Direct Memory Access (RDMA) interfaces. A three-way handshake is +defined that must take place to establish that both the hypervisor and +management partition sides of the channel are running prior to +sending/receiving any of the protocol messages. + +This driver also utilizes Transport Event CRQs. CRQ messages are sent +when the hypervisor detects one of the peer partitions has abnormally +terminated, or one side has called H_FREE_CRQ to close their CRQ. +Two new classes of CRQ messages are introduced for the VMC device. VMC +Administrative messages are used for each partition using the VMC to +communicate capabilities to their partner. HMC Interface messages are used +for the actual flow of HMC messages between the management partition and +the hypervisor. As most HMC messages far exceed the size of a CRQ buffer, +a virtual DMA (RMDA) of the HMC message data is done prior to each HMC +Interface CRQ message. Only the management partition drives RDMA +operations; hypervisors never directly cause the movement of message data. + + +Terminology +----------- +RDMA + Remote Direct Memory Access is DMA transfer from the server to its + client or from the server to its partner partition. DMA refers + to both physical I/O to and from memory operations and to memory + to memory move operations. +CRQ + Command/Response Queue a facility which is used to communicate + between partner partitions. Transport events which are signaled + from the hypervisor to partition are also reported in this queue. + +Example Management Partition VMC Driver Interface +================================================= + +This section provides an example for the management application +implementation where a device driver is used to interface to the VMC +device. This driver consists of a new device, for example /dev/ibmvmc, +which provides interfaces to open, close, read, write, and perform +ioctl’s against the VMC device. + +VMC Interface Initialization +---------------------------- + +The device driver is responsible for initializing the VMC when the driver +is loaded. It first creates and initializes the CRQ. Next, an exchange of +VMC capabilities is performed to indicate the code version and number of +resources available in both the management partition and the hypervisor. +Finally, the hypervisor requests that the management partition create an +initial pool of VMC buffers, one buffer for each possible HMC connection, +which will be used for management application session initialization. +Prior to completion of this initialization sequence, the device returns +EBUSY to open() calls. EIO is returned for all open() failures. + +:: + + Management Partition Hypervisor + CRQ INIT + ----------------------------------------> + CRQ INIT COMPLETE + <---------------------------------------- + CAPABILITIES + ----------------------------------------> + CAPABILITIES RESPONSE + <---------------------------------------- + ADD BUFFER (HMC IDX=0,1,..) _ + <---------------------------------------- | + ADD BUFFER RESPONSE | - Perform # HMCs Iterations + ----------------------------------------> - + +VMC Interface Open +------------------ + +After the basic VMC channel has been initialized, an HMC session level +connection can be established. The application layer performs an open() to +the VMC device and executes an ioctl() against it, indicating the HMC ID +(32 bytes of data) for this session. If the VMC device is in an invalid +state, EIO will be returned for the ioctl(). The device driver creates a +new HMC session value (ranging from 1 to 255) and HMC index value (starting +at index 0 and ranging to 254) for this HMC ID. The driver then does an +RDMA of the HMC ID to the hypervisor, and then sends an Interface Open +message to the hypervisor to establish the session over the VMC. After the +hypervisor receives this information, it sends Add Buffer messages to the +management partition to seed an initial pool of buffers for the new HMC +connection. Finally, the hypervisor sends an Interface Open Response +message, to indicate that it is ready for normal runtime messaging. The +following illustrates this VMC flow: + +:: + + Management Partition Hypervisor + RDMA HMC ID + ----------------------------------------> + Interface Open + ----------------------------------------> + Add Buffer _ + <---------------------------------------- | + Add Buffer Response | - Perform N Iterations + ----------------------------------------> - + Interface Open Response + <---------------------------------------- + +VMC Interface Runtime +--------------------- + +During normal runtime, the management application and the hypervisor +exchange HMC messages via the Signal VMC message and RDMA operations. When +sending data to the hypervisor, the management application performs a +write() to the VMC device, and the driver RDMA’s the data to the hypervisor +and then sends a Signal Message. If a write() is attempted before VMC +device buffers have been made available by the hypervisor, or no buffers +are currently available, EBUSY is returned in response to the write(). A +write() will return EIO for all other errors, such as an invalid device +state. When the hypervisor sends a message to the management, the data is +put into a VMC buffer and an Signal Message is sent to the VMC driver in +the management partition. The driver RDMA’s the buffer into the partition +and passes the data up to the appropriate management application via a +read() to the VMC device. The read() request blocks if there is no buffer +available to read. The management application may use select() to wait for +the VMC device to become ready with data to read. + +:: + + Management Partition Hypervisor + MSG RDMA + ----------------------------------------> + SIGNAL MSG + ----------------------------------------> + SIGNAL MSG + <---------------------------------------- + MSG RDMA + <---------------------------------------- + +VMC Interface Close +------------------- + +HMC session level connections are closed by the management partition when +the application layer performs a close() against the device. This action +results in an Interface Close message flowing to the hypervisor, which +causes the session to be terminated. The device driver must free any +storage allocated for buffers for this HMC connection. + +:: + + Management Partition Hypervisor + INTERFACE CLOSE + ----------------------------------------> + INTERFACE CLOSE RESPONSE + <---------------------------------------- + +Additional Information +====================== + +For more information on the documentation for CRQ Messages, VMC Messages, +HMC interface Buffers, and signal messages please refer to the Linux on +Power Architecture Platform Reference. Section F. |