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diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst new file mode 100644 index 000000000..bbd548b66 --- /dev/null +++ b/Documentation/driver-api/vfio-mediated-device.rst @@ -0,0 +1,273 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. include:: <isonum.txt> + +===================== +VFIO Mediated devices +===================== + +:Copyright: |copy| 2016, NVIDIA CORPORATION. All rights reserved. +:Author: Neo Jia <cjia@nvidia.com> +:Author: Kirti Wankhede <kwankhede@nvidia.com> + + + +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_parent() +--------------+ + | | | +<------------------------+ | + | | | | | ccw_device.ko|<-> physical + | | | +------------------------>+ | device + | | | | callbacks +--------------+ + | | Physical | | + | | device | | mdev_register_parent() +--------------+ + | | interface | |<------------------------+ | + | | | | | i915.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 device driver provides the following +structure to represent a mediated device's driver:: + + /* + * struct mdev_driver [2] - Mediated device's driver + * @probe: called when new device created + * @remove: called when device removed + * @driver: device driver structure + */ + struct mdev_driver { + int (*probe) (struct mdev_device *dev); + void (*remove) (struct mdev_device *dev); + unsigned int (*get_available)(struct mdev_type *mtype); + ssize_t (*show_description)(struct mdev_type *mtype, char *buf); + 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:: + + int mdev_register_driver(struct mdev_driver *drv); + +* Unregister:: + + void mdev_unregister_driver(struct mdev_driver *drv); + +The mediated bus driver's probe function should create a vfio_device on top of +the mdev_device and connect it to an appropriate implementation of +vfio_device_ops. + +When a driver wants to add the GUID creation sysfs to an existing device it has +probe'd to then it should call:: + + int mdev_register_parent(struct mdev_parent *parent, struct device *dev, + struct mdev_driver *mdev_driver); + +This will provide the 'mdev_supported_types/XX/create' files which can then be +used to trigger the creation of a mdev_device. The created mdev_device will be +attached to the specified driver. + +When the driver needs to remove itself it calls:: + + void mdev_unregister_parent(struct mdev_parent *parent); + +Which will unbind and destroy all the created mdevs and remove the sysfs files. + +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 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 shows which device API is being created, for example, + "vfio-pci" for a PCI device. + +* available_instances + + This attribute shows 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 shows a human readable name. + +* description + + This attribute can show brief features/description of the type. This is an + 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:: + + int vfio_pin_pages(struct vfio_device *device, dma_addr_t iova, + int npage, int prot, struct page **pages); + + void vfio_unpin_pages(struct vfio_device *device, dma_addr_t iova, + int 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/driver-api/vfio.rst for more information on VFIO. +2. struct mdev_driver in include/linux/mdev.h +3. struct mdev_parent_ops in include/linux/mdev.h +4. struct vfio_iommu_driver_ops in include/linux/vfio.h |