From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops There's some internal state that ftrace_ops needs to have set, but since it can be declared outside of the ftrace.c code, it calls ftrace_ops_init() on the ops in every global function. The issue is that if two tasks call it on the same ops at the same time it is possible to have the initialization of one corrupt the initialization of the other call. Create a ops_mutex to use to synchronize every initialization of the ftrace_ops. The mutex is taken within checking the ftrace_ops flag that states it was initializied but the flag is checked again after the mutex has been taken. Checking first outside the mutex allows it to shortcut having to take the mutex. But then the check needs to be done again after the mute is taken in case of races. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock") Reported-by: sashiko-bot@kernel.org Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/ Signed-off-by: Steven Rostedt --- Documentation/driver-api/vfio-mediated-device.rst | 273 ++++++++++++++++++++++ 1 file changed, 273 insertions(+) create mode 100644 Documentation/driver-api/vfio-mediated-device.rst (limited to 'Documentation/driver-api/vfio-mediated-device.rst') 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:: + +===================== +VFIO Mediated devices +===================== + +:Copyright: |copy| 2016, NVIDIA CORPORATION. All rights reserved. +:Author: Neo Jia +:Author: Kirti Wankhede + + + +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] + | |--- [] + | | |--- create + | | |--- name + | | |--- available_instances + | | |--- device_api + | | |--- description + | | |--- [devices] + | |--- [] + | | |--- create + | | |--- name + | | |--- available_instances + | | |--- device_api + | | |--- description + | | |--- [devices] + | |--- [] + | |--- create + | |--- name + | |--- available_instances + | |--- device_api + | |--- description + | |--- [devices] + +* [mdev_supported_types] + + The list of currently supported mediated device types and their details. + + [], device_api, and available_instances are mandatory attributes + that should be provided by vendor driver. + +* [] + + The [] 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 that can be + created. + +* [device] + + This directory contains links to the devices of type 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 -- cgit v1.3.1