Merge tag 'drm-xe-next-2025-03-07' of https://gitlab.freedesktop.org/drm/xe/kernel into drm-next

.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)

===============

GPU SVM Section

===============

Agreed upon design principles

=============================

* migrate_to_ram path

	* Rely only on core MM concepts (migration PTEs, page references, and

	  page locking).

	* No driver specific locks other than locks for hardware interaction in

	  this path. These are not required and generally a bad idea to

	  invent driver defined locks to seal core MM races.

	* An example of a driver-specific lock causing issues occurred before

	  fixing do_swap_page to lock the faulting page. A driver-exclusive lock

	  in migrate_to_ram produced a stable livelock if enough threads read

	  the faulting page.

	* Partial migration is supported (i.e., a subset of pages attempting to

	  migrate can actually migrate, with only the faulting page guaranteed

	  to migrate).

	* Driver handles mixed migrations via retry loops rather than locking.

* Eviction

	* Eviction is defined as migrating data from the GPU back to the

	  CPU without a virtual address to free up GPU memory.

	* Only looking at physical memory data structures and locks as opposed to

	  looking at virtual memory data structures and locks.

	* No looking at mm/vma structs or relying on those being locked.

	* The rationale for the above two points is that CPU virtual addresses

	  can change at any moment, while the physical pages remain stable.

	* GPU page table invalidation, which requires a GPU virtual address, is

	  handled via the notifier that has access to the GPU virtual address.

* GPU fault side

	* mmap_read only used around core MM functions which require this lock

	  and should strive to take mmap_read lock only in GPU SVM layer.

	* Big retry loop to handle all races with the mmu notifier under the gpu

	  pagetable locks/mmu notifier range lock/whatever we end up calling

          those.

	* Races (especially against concurrent eviction or migrate_to_ram)

	  should not be handled on the fault side by trying to hold locks;

	  rather, they should be handled using retry loops. One possible

	  exception is holding a BO's dma-resv lock during the initial migration

	  to VRAM, as this is a well-defined lock that can be taken underneath

	  the mmap_read lock.

	* One possible issue with the above approach is if a driver has a strict

	  migration policy requiring GPU access to occur in GPU memory.

	  Concurrent CPU access could cause a livelock due to endless retries.

	  While no current user (Xe) of GPU SVM has such a policy, it is likely

	  to be added in the future. Ideally, this should be resolved on the

	  core-MM side rather than through a driver-side lock.

* Physical memory to virtual backpointer

	* This does not work, as no pointers from physical memory to virtual

	  memory should exist. mremap() is an example of the core MM updating

	  the virtual address without notifying the driver of address

	  change rather the driver only receiving the invalidation notifier.

	* The physical memory backpointer (page->zone_device_data) should remain

	  stable from allocation to page free. Safely updating this against a

	  concurrent user would be very difficult unless the page is free.

* GPU pagetable locking

	* Notifier lock only protects range tree, pages valid state for a range

	  (rather than seqno due to wider notifiers), pagetable entries, and

	  mmu notifier seqno tracking, it is not a global lock to protect

          against races.

	* All races handled with big retry as mentioned above.

Overview of baseline design

===========================

Baseline design is simple as possible to get a working basline in which can be

built upon.

.. kernel-doc:: drivers/gpu/drm/xe/drm_gpusvm.c

   :doc: Overview

   :doc: Locking

   :doc: Migrataion

   :doc: Partial Unmapping of Ranges

   :doc: Examples

Possible future design features

===============================

* Concurrent GPU faults

	* CPU faults are concurrent so makes sense to have concurrent GPU

	  faults.

	* Should be possible with fined grained locking in the driver GPU

	  fault handler.

	* No expected GPU SVM changes required.

* Ranges with mixed system and device pages

	* Can be added if required to drm_gpusvm_get_pages fairly easily.

* Multi-GPU support

	* Work in progress and patches expected after initially landing on GPU

	  SVM.

	* Ideally can be done with little to no changes to GPU SVM.

* Drop ranges in favor of radix tree

	* May be desirable for faster notifiers.

* Compound device pages

	* Nvidia, AMD, and Intel all have agreed expensive core MM functions in

	  migrate device layer are a performance bottleneck, having compound

	  device pages should help increase performance by reducing the number

	  of these expensive calls.

* Higher order dma mapping for migration

	* 4k dma mapping adversely affects migration performance on Intel

	  hardware, higher order (2M) dma mapping should help here.

* Build common userptr implementation on top of GPU SVM

* Driver side madvise implementation and migration policies

* Pull in pending dma-mapping API changes from Leon / Nvidia when these land

* Once the code has landed move all the documentation to the right places in

  the main core, helper or driver sections.

.. toctree::

    gpusvm.rst

.. toctree::

    i915_gem_lmem.rst

{

	WARN_ON(!component->bound);

	dev_dbg(adev->parent, "unbinding %s component %p (ops %ps)\n",

		dev_name(component->dev), component, component->ops);

	if (component->ops && component->ops->unbind)

		component->ops->unbind(component->dev, adev->parent, data);

	component->bound = false;

}

EXPORT_SYMBOL_GPL(devres_open_group);

/* Find devres group with ID @id.  If @id is NULL, look for the latest. */

/*

 * Find devres group with ID @id.  If @id is NULL, look for the latest open

 * group.

 */

static struct devres_group *find_group(struct device *dev, void *id)

{

	struct devres_node *node;

		spin_unlock_irqrestore(&dev->devres_lock, flags);

		release_nodes(dev, &todo);

	} else if (list_empty(&dev->devres_head)) {

		/*

		 * dev is probably dying via devres_release_all(): groups

		 * have already been removed and are on the process of

		 * being released - don't touch and don't warn.

		 */

		spin_unlock_irqrestore(&dev->devres_lock, flags);

	} else {

		WARN_ON(1);

		spin_unlock_irqrestore(&dev->devres_lock, flags);

	  GPU-VM representation providing helpers to manage a GPUs virtual

	  address space

config DRM_GPUSVM

	tristate

	depends on DRM && DEVICE_PRIVATE

	select HMM_MIRROR

	select MMU_NOTIFIER

	help

	  GPU-SVM representation providing helpers to manage a GPUs shared

	  virtual memory

config DRM_BUDDY

	tristate

	depends on DRM