274 lines
9.5 KiB
ReStructuredText
274 lines
9.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
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.. include:: <isonum.txt>
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=====================
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VFIO Mediated devices
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=====================
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:Copyright: |copy| 2016, NVIDIA CORPORATION. All rights reserved.
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:Author: Neo Jia <cjia@nvidia.com>
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:Author: Kirti Wankhede <kwankhede@nvidia.com>
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Virtual Function I/O (VFIO) Mediated devices[1]
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===============================================
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The number of use cases for virtualizing DMA devices that do not have built-in
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SR_IOV capability is increasing. Previously, to virtualize such devices,
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developers had to create their own management interfaces and APIs, and then
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integrate them with user space software. To simplify integration with user space
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software, we have identified common requirements and a unified management
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interface for such devices.
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The VFIO driver framework provides unified APIs for direct device access. It is
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an IOMMU/device-agnostic framework for exposing direct device access to user
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space in a secure, IOMMU-protected environment. This framework is used for
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multiple devices, such as GPUs, network adapters, and compute accelerators. With
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direct device access, virtual machines or user space applications have direct
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access to the physical device. This framework is reused for mediated devices.
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The mediated core driver provides a common interface for mediated device
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management that can be used by drivers of different devices. This module
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provides a generic interface to perform these operations:
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* Create and destroy a mediated device
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* Add a mediated device to and remove it from a mediated bus driver
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* Add a mediated device to and remove it from an IOMMU group
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The mediated core driver also provides an interface to register a bus driver.
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For example, the mediated VFIO mdev driver is designed for mediated devices and
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supports VFIO APIs. The mediated bus driver adds a mediated device to and
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removes it from a VFIO group.
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The following high-level block diagram shows the main components and interfaces
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in the VFIO mediated driver framework. The diagram shows NVIDIA, Intel, and IBM
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devices as examples, as these devices are the first devices to use this module::
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+---------------+
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| |
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| +-----------+ | mdev_register_driver() +--------------+
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| | | +<------------------------+ |
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| | mdev | | | |
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| | bus | +------------------------>+ vfio_mdev.ko |<-> VFIO user
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| | driver | | probe()/remove() | | APIs
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| | | | +--------------+
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| +-----------+ |
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| MDEV CORE |
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| MODULE |
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| mdev.ko |
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| +-----------+ | mdev_register_parent() +--------------+
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| | | +<------------------------+ |
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| | | | | ccw_device.ko|<-> physical
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| | | +------------------------>+ | device
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| | | | callbacks +--------------+
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| | Physical | |
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| | device | | mdev_register_parent() +--------------+
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| | interface | |<------------------------+ |
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| | | | | i915.ko |<-> physical
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| | | +------------------------>+ | device
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| | | | callbacks +--------------+
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| +-----------+ |
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+---------------+
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Registration Interfaces
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=======================
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The mediated core driver provides the following types of registration
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interfaces:
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* Registration interface for a mediated bus driver
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* Physical device driver interface
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Registration Interface for a Mediated Bus Driver
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------------------------------------------------
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The registration interface for a mediated device driver provides the following
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structure to represent a mediated device's driver::
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/*
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* struct mdev_driver [2] - Mediated device's driver
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* @probe: called when new device created
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* @remove: called when device removed
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* @driver: device driver structure
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*/
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struct mdev_driver {
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int (*probe) (struct mdev_device *dev);
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void (*remove) (struct mdev_device *dev);
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unsigned int (*get_available)(struct mdev_type *mtype);
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ssize_t (*show_description)(struct mdev_type *mtype, char *buf);
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struct device_driver driver;
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};
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A mediated bus driver for mdev should use this structure in the function calls
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to register and unregister itself with the core driver:
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* Register::
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int mdev_register_driver(struct mdev_driver *drv);
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* Unregister::
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void mdev_unregister_driver(struct mdev_driver *drv);
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The mediated bus driver's probe function should create a vfio_device on top of
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the mdev_device and connect it to an appropriate implementation of
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vfio_device_ops.
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When a driver wants to add the GUID creation sysfs to an existing device it has
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probe'd to then it should call::
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int mdev_register_parent(struct mdev_parent *parent, struct device *dev,
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struct mdev_driver *mdev_driver);
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This will provide the 'mdev_supported_types/XX/create' files which can then be
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used to trigger the creation of a mdev_device. The created mdev_device will be
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attached to the specified driver.
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When the driver needs to remove itself it calls::
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void mdev_unregister_parent(struct mdev_parent *parent);
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Which will unbind and destroy all the created mdevs and remove the sysfs files.
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Mediated Device Management Interface Through sysfs
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==================================================
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The management interface through sysfs enables user space software, such as
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libvirt, to query and configure mediated devices in a hardware-agnostic fashion.
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This management interface provides flexibility to the underlying physical
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device's driver to support features such as:
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* Mediated device hot plug
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* Multiple mediated devices in a single virtual machine
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* Multiple mediated devices from different physical devices
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Links in the mdev_bus Class Directory
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-------------------------------------
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The /sys/class/mdev_bus/ directory contains links to devices that are registered
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with the mdev core driver.
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Directories and files under the sysfs for Each Physical Device
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--------------------------------------------------------------
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::
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|- [parent physical device]
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|--- Vendor-specific-attributes [optional]
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|--- [mdev_supported_types]
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| |--- [<type-id>]
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| | |--- create
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| | |--- name
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| | |--- available_instances
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| | |--- device_api
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| | |--- description
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| | |--- [devices]
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| |--- [<type-id>]
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| | |--- create
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| | |--- name
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| | |--- available_instances
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| | |--- device_api
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| | |--- description
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| | |--- [devices]
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| |--- [<type-id>]
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| |--- create
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| |--- name
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| |--- available_instances
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| |--- device_api
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| |--- description
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| |--- [devices]
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* [mdev_supported_types]
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The list of currently supported mediated device types and their details.
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[<type-id>], device_api, and available_instances are mandatory attributes
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that should be provided by vendor driver.
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* [<type-id>]
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The [<type-id>] name is created by adding the device driver string as a prefix
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to the string provided by the vendor driver. This format of this name is as
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follows::
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sprintf(buf, "%s-%s", dev_driver_string(parent->dev), group->name);
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* device_api
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This attribute shows which device API is being created, for example,
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"vfio-pci" for a PCI device.
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* available_instances
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This attribute shows the number of devices of type <type-id> that can be
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created.
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* [device]
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This directory contains links to the devices of type <type-id> that have been
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created.
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* name
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This attribute shows a human readable name.
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* description
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This attribute can show brief features/description of the type. This is an
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optional attribute.
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Directories and Files Under the sysfs for Each mdev Device
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----------------------------------------------------------
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::
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|- [parent phy device]
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|--- [$MDEV_UUID]
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|--- remove
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|--- mdev_type {link to its type}
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|--- vendor-specific-attributes [optional]
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* remove (write only)
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Writing '1' to the 'remove' file destroys the mdev device. The vendor driver can
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fail the remove() callback if that device is active and the vendor driver
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doesn't support hot unplug.
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Example::
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# echo 1 > /sys/bus/mdev/devices/$mdev_UUID/remove
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Mediated device Hot plug
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------------------------
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Mediated devices can be created and assigned at runtime. The procedure to hot
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plug a mediated device is the same as the procedure to hot plug a PCI device.
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Translation APIs for Mediated Devices
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=====================================
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The following APIs are provided for translating user pfn to host pfn in a VFIO
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driver::
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int vfio_pin_pages(struct vfio_device *device, dma_addr_t iova,
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int npage, int prot, struct page **pages);
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void vfio_unpin_pages(struct vfio_device *device, dma_addr_t iova,
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int npage);
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These functions call back into the back-end IOMMU module by using the pin_pages
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and unpin_pages callbacks of the struct vfio_iommu_driver_ops[4]. Currently
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these callbacks are supported in the TYPE1 IOMMU module. To enable them for
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other IOMMU backend modules, such as PPC64 sPAPR module, they need to provide
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these two callback functions.
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References
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==========
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1. See Documentation/driver-api/vfio.rst for more information on VFIO.
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2. struct mdev_driver in include/linux/mdev.h
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3. struct mdev_parent_ops in include/linux/mdev.h
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4. struct vfio_iommu_driver_ops in include/linux/vfio.h
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