Add file Documentation/vfio-mediated-device.txt that include details of
mediated device framework.
Signed-off-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
Signed-off-by: Neo Jia <cjia@xxxxxxxxxx>
Change-Id: I137dd646442936090d92008b115908b7b2c7bc5d
---
Documentation/vfio-mediated-device.txt | 298 +++++++++++++++++++++++++++++++++
1 file changed, 298 insertions(+)
create mode 100644 Documentation/vfio-mediated-device.txt
diff --git a/Documentation/vfio-mediated-device.txt b/Documentation/vfio-mediated-device.txt
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+/*
+ * VFIO Mediated devices
+ *
+ * Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
+ * Author: Neo Jia <cjia@xxxxxxxxxx>
+ * Kirti Wankhede <kwankhede@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+Virtual Function I/O (VFIO) Mediated devices[1]
+===============================================
+
+The number of use cases for virtualizing DMA devices that do not have built-in
+SR_IOV capability is increasing. Previously, to virtualize such devices,
+developers had to create their own management interfaces and APIs, and then
+integrate them with user space software. To simplify integration with user space
+software, we have identified common requirements and a unified management
+interface for such devices.
+
+The VFIO driver framework provides unified APIs for direct device access. It is
+an IOMMU/device-agnostic framework for exposing direct device access to user
+space in a secure, IOMMU-protected environment. This framework is used for
+multiple devices, such as GPUs, network adapters, and compute accelerators. With
+direct device access, virtual machines or user space applications have direct
+access to the physical device. This framework is reused for mediated devices.
+
+The mediated core driver provides a common interface for mediated device
+management that can be used by drivers of different devices. This module
+provides a generic interface to perform these operations:
+
+* Create and destroy a mediated device
+* Add a mediated device to and remove it from a mediated bus driver
+* Add a mediated device to and remove it from an IOMMU group
+
+The mediated core driver also provides an interface to register a bus driver.
+For example, the mediated VFIO mdev driver is designed for mediated devices and
+supports VFIO APIs. The mediated bus driver adds a mediated device to and
+removes it from a VFIO group.
+
+The following high-level block diagram shows the main components and interfaces
+in the VFIO mediated driver framework. The diagram shows NVIDIA, Intel, and IBM
+devices as examples, as these devices are the first devices to use this module.
+
+ +---------------+
+ | |
+ | +-----------+ | mdev_register_driver() +--------------+
+ | | | +<------------------------+ |
+ | | mdev | | | |
+ | | bus | +------------------------>+ vfio_mdev.ko |<-> VFIO user
+ | | driver | | probe()/remove() | | APIs
+ | | | | +--------------+
+ | +-----------+ |
+ | |
+ | MDEV CORE |
+ | MODULE |
+ | mdev.ko |
+ | +-----------+ | mdev_register_device() +--------------+
+ | | | +<------------------------+ |
+ | | | | | nvidia.ko |<-> physical
+ | | | +------------------------>+ | device
+ | | | | callbacks +--------------+
+ | | Physical | |
+ | | device | | mdev_register_device() +--------------+
+ | | interface | |<------------------------+ |
+ | | | | | i915.ko |<-> physical
+ | | | +------------------------>+ | device
+ | | | | callbacks +--------------+
+ | | | |
+ | | | | mdev_register_device() +--------------+
+ | | | +<------------------------+ |
+ | | | | | ccw_device.ko|<-> physical
+ | | | +------------------------>+ | device
+ | | | | callbacks +--------------+
+ | +-----------+ |
+ +---------------+
+
+
+Registration Interfaces
+=======================
+
+The mediated core driver provides the following types of registration
+interfaces:
+
+* Registration interface for a mediated bus driver
+* Physical device driver interface
+
+Registration Interface for a Mediated Bus Driver
+------------------------------------------------
+
+The registration interface for a mediated bus driver provides the following
+structure to represent a mediated device's driver:
+
+ /*
+ * struct mdev_driver [2] - Mediated device's driver
+ * @name: driver name
+ * @probe: called when new device created
+ * @remove: called when device removed
+ * @driver: device driver structure
+ */
+ struct mdev_driver {
+ const char *name;
+ int (*probe) (struct device *dev);
+ void (*remove) (struct device *dev);
+ struct device_driver driver;
+ };
+
+A mediated bus driver for mdev should use this structure in the function calls
+to register and unregister itself with the core driver:
+
+* Register:
+
+ extern int mdev_register_driver(struct mdev_driver *drv,
+ struct module *owner);
+
+* Unregister:
+
+ extern void mdev_unregister_driver(struct mdev_driver *drv);
+
+The mediated bus driver is responsible for adding mediated devices to the VFIO
+group when devices are bound to the driver and removing mediated devices from
+the VFIO when devices are unbound from the driver.
+
+
+Physical Device Driver Interface
+--------------------------------
+
+The physical device driver interface provides the parent_ops[3] structure to
+define the APIs to manage work in the mediated core driver that is related to
+the physical device.
+
+The structures in the parent_ops structure are as follows:
+
+* dev_attr_groups: attributes of the parent device
+* mdev_attr_groups: attributes of the mediated device
+* supported_config: attributes to define supported configurations
+
+The functions in the parent_ops structure are as follows:
+
+* create: allocate basic resources in a driver for a mediated device
+* remove: free resources in a driver when a mediated device is destroyed
+
+The callbacks in the parent_ops structure are as follows:
+
+* open: open callback of mediated device
+* close: close callback of mediated device
+* ioctl: ioctl callback of mediated device
+* read : read emulation callback
+* write: write emulation callback
+* mmap: mmap emulation callback
+* notifier: notifier callback
+
+A driver should use the parent_ops structure in the function call to register
+itself with the mdev core driver:
+
+extern int mdev_register_device(struct device *dev,
+ const struct parent_ops *ops);
+
+However, the parent_ops structure is not required in the function call that a
+driver should use to unregister itself with the mdev core driver:
+
+extern void mdev_unregister_device(struct device *dev);
+
+
+Mediated Device Management Interface Through sysfs
+==================================================
+
+The management interface through sysfs enables user space software, such as
+libvirt, to query and configure mediated devices in a hardware-agnostic fashion.
+This management interface provides flexibility to the underlying physical
+device's driver to support features such as:
+
+* Mediated device hot plug
+* Multiple mediated devices in a single virtual machine
+* Multiple mediated devices from different physical devices
+
+Links in the mdev_bus Class Directory
+-------------------------------------
+The /sys/class/mdev_bus/ directory contains links to devices that are registered
+with the mdev core driver.
+
+Directories and files under the sysfs for Each Physical Device
+--------------------------------------------------------------
+
+|- [parent physical device]
+|--- Vendor-specific-attributes [optional]
+|--- [mdev_supported_types]
+| |--- [<type-id>]
+| | |--- create
+| | |--- name
+| | |--- available_instances
+| | |--- device_api
+| | |--- description
+| | |--- [devices]
+| |--- [<type-id>]
+| | |--- create
+| | |--- name
+| | |--- available_instances
+| | |--- device_api
+| | |--- description
+| | |--- [devices]
+| |--- [<type-id>]
+| |--- create
+| |--- name
+| |--- available_instances
+| |--- device_api
+| |--- description
+| |--- [devices]
+
+* [mdev_supported_types]
+
+ The list of currently supported mediated device types and their details.
+
+ [<type-id>], device_api, and available_instances are mandatory attributes
+ that should be provided by vendor driver.
+
+* [<type-id>]
+
+ The [<type-id>] name is created by adding the the device driver string as a
+ prefix to the string provided by the vendor driver. This format of this name
+ is as follows:
+
+ sprintf(buf, "%s-%s", dev_driver_string(parent->dev), group->name);
+
+* device_api
+
+ This attribute should show which device API is being created, for example,
+ "vfio-pci" for a PCI device.
+
+* available_instances
+
+ This attribute should show the number of devices of type <type-id> that can be
+ created.
+
+* [device]
+
+ This directory contains links to the devices of type <type-id> that have been
+created.
+
+* name
+
+ This attribute should show human readable name. This is optional attribute.
+
+* description
+
+ This attribute should show brief features/description of the type. This is
+ optional attribute.
+
+Directories and Files Under the sysfs for Each mdev Device
+----------------------------------------------------------
+
+|- [parent phy device]
+|--- [$MDEV_UUID]
+ |--- remove
+ |--- mdev_type {link to its type}
+ |--- vendor-specific-attributes [optional]
+
+* remove (write only)
+Writing '1' to the 'remove' file destroys the mdev device. The vendor driver can
+fail the remove() callback if that device is active and the vendor driver
+doesn't support hot unplug.
+
+Example:
+ # echo 1 > /sys/bus/mdev/devices/$mdev_UUID/remove
+
+Mediated device Hot plug:
+------------------------
+
+Mediated devices can be created and assigned at runtime. The procedure to hot
+plug a mediated device is the same as the procedure to hot plug a PCI device.
+
+Translation APIs for Mediated Devices
+=====================================
+
+The following APIs are provided for translating user pfn to host pfn in a VFIO
+driver:
+
+ extern long vfio_pin_pages(struct device *dev, unsigned long *user_pfn,
+ long npage, int prot, unsigned long *phys_pfn);
+
+ extern long vfio_unpin_pages(struct device *dev, unsigned long *pfn,
+ long npage);
+
+These functions call back into the back-end IOMMU module by using the pin_pages
+and unpin_pages callbacks of the struct vfio_iommu_driver_ops[4]. Currently
+these callbacks are supported in the TYPE1 IOMMU module. To enable them for
+other IOMMU backend modules, such as PPC64 sPAPR module, they need to provide
+these two callback functions.
+
+References
+----------
+
+[1] See Documentation/vfio.txt for more information on VFIO.
+[2] struct mdev_driver in include/linux/mdev.h
+[3] struct parent_ops in include/linux/mdev.h
+[4] struct vfio_iommu_driver_ops in include/linux/vfio.h
--
2.7.0
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