// SPDX-License-Identifier: GPL-2.0-only OR MIT
/*
 * Copyright © 2024 Intel Corporation
 *
 * Authors:
 *     Matthew Brost <matthew.brost@intel.com>
 */

#include <linux/dma-mapping.h>
#include <linux/export.h>
#include <linux/hmm.h>
#include <linux/hugetlb_inline.h>
#include <linux/memremap.h>
#include <linux/mm_types.h>
#include <linux/slab.h>

#include <drm/drm_device.h>
#include <drm/drm_gpusvm.h>
#include <drm/drm_pagemap.h>
#include <drm/drm_print.h>

/**
 * DOC: Overview
 *
 * GPU Shared Virtual Memory (GPU SVM) layer for the Direct Rendering Manager (DRM)
 * is a component of the DRM framework designed to manage shared virtual memory
 * between the CPU and GPU. It enables efficient data exchange and processing
 * for GPU-accelerated applications by allowing memory sharing and
 * synchronization between the CPU's and GPU's virtual address spaces.
 *
 * Key GPU SVM Components:
 *
 * - Notifiers:
 *      Used for tracking memory intervals and notifying the GPU of changes,
 *      notifiers are sized based on a GPU SVM initialization parameter, with a
 *      recommendation of 512M or larger. They maintain a Red-BlacK tree and a
 *      list of ranges that fall within the notifier interval.  Notifiers are
 *      tracked within a GPU SVM Red-BlacK tree and list and are dynamically
 *      inserted or removed as ranges within the interval are created or
 *      destroyed.
 * - Ranges:
 *      Represent memory ranges mapped in a DRM device and managed by GPU SVM.
 *      They are sized based on an array of chunk sizes, which is a GPU SVM
 *      initialization parameter, and the CPU address space.  Upon GPU fault,
 *      the largest aligned chunk that fits within the faulting CPU address
 *      space is chosen for the range size. Ranges are expected to be
 *      dynamically allocated on GPU fault and removed on an MMU notifier UNMAP
 *      event. As mentioned above, ranges are tracked in a notifier's Red-Black
 *      tree.
 *
 * - Operations:
 *      Define the interface for driver-specific GPU SVM operations such as
 *      range allocation, notifier allocation, and invalidations.
 *
 * - Device Memory Allocations:
 *      Embedded structure containing enough information for GPU SVM to migrate
 *      to / from device memory.
 *
 * - Device Memory Operations:
 *      Define the interface for driver-specific device memory operations
 *      release memory, populate pfns, and copy to / from device memory.
 *
 * This layer provides interfaces for allocating, mapping, migrating, and
 * releasing memory ranges between the CPU and GPU. It handles all core memory
 * management interactions (DMA mapping, HMM, and migration) and provides
 * driver-specific virtual functions (vfuncs). This infrastructure is sufficient
 * to build the expected driver components for an SVM implementation as detailed
 * below.
 *
 * Expected Driver Components:
 *
 * - GPU page fault handler:
 *      Used to create ranges and notifiers based on the fault address,
 *      optionally migrate the range to device memory, and create GPU bindings.
 *
 * - Garbage collector:
 *      Used to unmap and destroy GPU bindings for ranges.  Ranges are expected
 *      to be added to the garbage collector upon a MMU_NOTIFY_UNMAP event in
 *      notifier callback.
 *
 * - Notifier callback:
 *      Used to invalidate and DMA unmap GPU bindings for ranges.
 */

/**
 * DOC: Locking
 *
 * GPU SVM handles locking for core MM interactions, i.e., it locks/unlocks the
 * mmap lock as needed.
 *
 * GPU SVM introduces a global notifier lock, which safeguards the notifier's
 * range RB tree and list, as well as the range's DMA mappings and sequence
 * number. GPU SVM manages all necessary locking and unlocking operations,
 * except for the recheck range's pages being valid
 * (drm_gpusvm_range_pages_valid) when the driver is committing GPU bindings.
 * This lock corresponds to the ``driver->update`` lock mentioned in
 * Documentation/mm/hmm.rst. Future revisions may transition from a GPU SVM
 * global lock to a per-notifier lock if finer-grained locking is deemed
 * necessary.
 *
 * In addition to the locking mentioned above, the driver should implement a
 * lock to safeguard core GPU SVM function calls that modify state, such as
 * drm_gpusvm_range_find_or_insert and drm_gpusvm_range_remove. This lock is
 * denoted as 'driver_svm_lock' in code examples. Finer grained driver side
 * locking should also be possible for concurrent GPU fault processing within a
 * single GPU SVM. The 'driver_svm_lock' can be via drm_gpusvm_driver_set_lock
 * to add annotations to GPU SVM.
 */

/**
 * DOC: Partial Unmapping of Ranges
 *
 * Partial unmapping of ranges (e.g., 1M out of 2M is unmapped by CPU resulting
 * in MMU_NOTIFY_UNMAP event) presents several challenges, with the main one
 * being that a subset of the range still has CPU and GPU mappings. If the
 * backing store for the range is in device memory, a subset of the backing
 * store has references. One option would be to split the range and device
 * memory backing store, but the implementation for this would be quite
 * complicated. Given that partial unmappings are rare and driver-defined range
 * sizes are relatively small, GPU SVM does not support splitting of ranges.
 *
 * With no support for range splitting, upon partial unmapping of a range, the
 * driver is expected to invalidate and destroy the entire range. If the range
 * has device memory as its backing, the driver is also expected to migrate any
 * remaining pages back to RAM.
 */

/**
 * DOC: Examples
 *
 * This section provides three examples of how to build the expected driver
 * components: the GPU page fault handler, the garbage collector, and the
 * notifier callback.
 *
 * The generic code provided does not include logic for complex migration
 * policies, optimized invalidations, fined grained driver locking, or other
 * potentially required driver locking (e.g., DMA-resv locks).
 *
 * 1) GPU page fault handler
 *
 * .. code-block:: c
 *
 *      int driver_bind_range(struct drm_gpusvm *gpusvm, struct drm_gpusvm_range *range)
 *      {
 *              int err = 0;
 *
 *              driver_alloc_and_setup_memory_for_bind(gpusvm, range);
 *
 *              drm_gpusvm_notifier_lock(gpusvm);
 *              if (drm_gpusvm_range_pages_valid(range))
 *                      driver_commit_bind(gpusvm, range);
 *              else
 *                      err = -EAGAIN;
 *              drm_gpusvm_notifier_unlock(gpusvm);
 *
 *              return err;
 *      }
 *
 *      int driver_gpu_fault(struct drm_gpusvm *gpusvm, unsigned long fault_addr,
 *                           unsigned long gpuva_start, unsigned long gpuva_end)
 *      {
 *              struct drm_gpusvm_ctx ctx = {};
 *              int err;
 *
 *              driver_svm_lock();
 *      retry:
 *              // Always process UNMAPs first so view of GPU SVM ranges is current
 *              driver_garbage_collector(gpusvm);
 *
 *              range = drm_gpusvm_range_find_or_insert(gpusvm, fault_addr,
 *                                                      gpuva_start, gpuva_end,
 *                                                      &ctx);
 *              if (IS_ERR(range)) {
 *                      err = PTR_ERR(range);
 *                      goto unlock;
 *              }
 *
 *              if (driver_migration_policy(range)) {
 *                      err = drm_pagemap_populate_mm(driver_choose_drm_pagemap(),
 *                                                    gpuva_start, gpuva_end, gpusvm->mm,
 *                                                    ctx->timeslice_ms);
 *                      if (err)        // CPU mappings may have changed
 *                              goto retry;
 *              }
 *
 *              err = drm_gpusvm_range_get_pages(gpusvm, range, &ctx);
 *              if (err == -EOPNOTSUPP || err == -EFAULT || err == -EPERM) {    // CPU mappings changed
 *                      if (err == -EOPNOTSUPP)
 *                              drm_gpusvm_range_evict(gpusvm, range);
 *                      goto retry;
 *              } else if (err) {
 *                      goto unlock;
 *              }
 *
 *              err = driver_bind_range(gpusvm, range);
 *              if (err == -EAGAIN)     // CPU mappings changed
 *                      goto retry
 *
 *      unlock:
 *              driver_svm_unlock();
 *              return err;
 *      }
 *
 * 2) Garbage Collector
 *
 * .. code-block:: c
 *
 *      void __driver_garbage_collector(struct drm_gpusvm *gpusvm,
 *                                      struct drm_gpusvm_range *range)
 *      {
 *              assert_driver_svm_locked(gpusvm);
 *
 *              // Partial unmap, migrate any remaining device memory pages back to RAM
 *              if (range->flags.partial_unmap)
 *                      drm_gpusvm_range_evict(gpusvm, range);
 *
 *              driver_unbind_range(range);
 *              drm_gpusvm_range_remove(gpusvm, range);
 *      }
 *
 *      void driver_garbage_collector(struct drm_gpusvm *gpusvm)
 *      {
 *              assert_driver_svm_locked(gpusvm);
 *
 *              for_each_range_in_garbage_collector(gpusvm, range)
 *                      __driver_garbage_collector(gpusvm, range);
 *      }
 *
 * 3) Notifier callback
 *
 * .. code-block:: c
 *
 *      void driver_invalidation(struct drm_gpusvm *gpusvm,
 *                               struct drm_gpusvm_notifier *notifier,
 *                               const struct mmu_notifier_range *mmu_range)
 *      {
 *              struct drm_gpusvm_ctx ctx = { .in_notifier = true, };
 *              struct drm_gpusvm_range *range = NULL;
 *
 *              driver_invalidate_device_pages(gpusvm, mmu_range->start, mmu_range->end);
 *
 *              drm_gpusvm_for_each_range(range, notifier, mmu_range->start,
 *                                        mmu_range->end) {
 *                      drm_gpusvm_range_unmap_pages(gpusvm, range, &ctx);
 *
 *                      if (mmu_range->event != MMU_NOTIFY_UNMAP)
 *                              continue;
 *
 *                      drm_gpusvm_range_set_unmapped(range, mmu_range);
 *                      driver_garbage_collector_add(gpusvm, range);
 *              }
 *      }
 */

/**
 * npages_in_range() - Calculate the number of pages in a given range
 * @start: The start address of the range
 * @end: The end address of the range
 *
 * This macro calculates the number of pages in a given memory range,
 * specified by the start and end addresses. It divides the difference
 * between the end and start addresses by the page size (PAGE_SIZE) to
 * determine the number of pages in the range.
 *
 * Return: The number of pages in the specified range.
 */
static unsigned long
npages_in_range(unsigned long start, unsigned long end)
{
        return (end - start) >> PAGE_SHIFT;
}

/**
 * drm_gpusvm_notifier_find() - Find GPU SVM notifier from GPU SVM
 * @gpusvm: Pointer to the GPU SVM structure.
 * @start: Start address of the notifier
 * @end: End address of the notifier
 *
 * Return: A pointer to the drm_gpusvm_notifier if found or NULL
 */
struct drm_gpusvm_notifier *
drm_gpusvm_notifier_find(struct drm_gpusvm *gpusvm, unsigned long start,
                         unsigned long end)
{
        struct interval_tree_node *itree;

        itree = interval_tree_iter_first(&gpusvm->root, start, end - 1);

        if (itree)
                return container_of(itree, struct drm_gpusvm_notifier, itree);
        else
                return NULL;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_notifier_find);

/**
 * drm_gpusvm_range_find() - Find GPU SVM range from GPU SVM notifier
 * @notifier: Pointer to the GPU SVM notifier structure.
 * @start: Start address of the range
 * @end: End address of the range
 *
 * Return: A pointer to the drm_gpusvm_range if found or NULL
 */
struct drm_gpusvm_range *
drm_gpusvm_range_find(struct drm_gpusvm_notifier *notifier, unsigned long start,
                      unsigned long end)
{
        struct interval_tree_node *itree;

        itree = interval_tree_iter_first(&notifier->root, start, end - 1);

        if (itree)
                return container_of(itree, struct drm_gpusvm_range, itree);
        else
                return NULL;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_find);

/**
 * drm_gpusvm_notifier_invalidate() - Invalidate a GPU SVM notifier.
 * @mni: Pointer to the mmu_interval_notifier structure.
 * @mmu_range: Pointer to the mmu_notifier_range structure.
 * @cur_seq: Current sequence number.
 *
 * This function serves as a generic MMU notifier for GPU SVM. It sets the MMU
 * notifier sequence number and calls the driver invalidate vfunc under
 * gpusvm->notifier_lock.
 *
 * Return: true if the operation succeeds, false otherwise.
 */
static bool
drm_gpusvm_notifier_invalidate(struct mmu_interval_notifier *mni,
                               const struct mmu_notifier_range *mmu_range,
                               unsigned long cur_seq)
{
        struct drm_gpusvm_notifier *notifier =
                container_of(mni, typeof(*notifier), notifier);
        struct drm_gpusvm *gpusvm = notifier->gpusvm;

        if (!mmu_notifier_range_blockable(mmu_range))
                return false;

        down_write(&gpusvm->notifier_lock);
        mmu_interval_set_seq(mni, cur_seq);
        gpusvm->ops->invalidate(gpusvm, notifier, mmu_range);
        up_write(&gpusvm->notifier_lock);

        return true;
}

/*
 * drm_gpusvm_notifier_ops - MMU interval notifier operations for GPU SVM
 */
static const struct mmu_interval_notifier_ops drm_gpusvm_notifier_ops = {
        .invalidate = drm_gpusvm_notifier_invalidate,
};

/**
 * drm_gpusvm_init() - Initialize the GPU SVM.
 * @gpusvm: Pointer to the GPU SVM structure.
 * @name: Name of the GPU SVM.
 * @drm: Pointer to the DRM device structure.
 * @mm: Pointer to the mm_struct for the address space.
 * @mm_start: Start address of GPU SVM.
 * @mm_range: Range of the GPU SVM.
 * @notifier_size: Size of individual notifiers.
 * @ops: Pointer to the operations structure for GPU SVM.
 * @chunk_sizes: Pointer to the array of chunk sizes used in range allocation.
 *               Entries should be powers of 2 in descending order with last
 *               entry being SZ_4K.
 * @num_chunks: Number of chunks.
 *
 * This function initializes the GPU SVM.
 *
 * Note: If only using the simple drm_gpusvm_pages API (get/unmap/free),
 * then only @gpusvm, @name, and @drm are expected. However, the same base
 * @gpusvm can also be used with both modes together in which case the full
 * setup is needed, where the core drm_gpusvm_pages API will simply never use
 * the other fields.
 *
 * Return: 0 on success, a negative error code on failure.
 */
int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
                    const char *name, struct drm_device *drm,
                    struct mm_struct *mm,
                    unsigned long mm_start, unsigned long mm_range,
                    unsigned long notifier_size,
                    const struct drm_gpusvm_ops *ops,
                    const unsigned long *chunk_sizes, int num_chunks)
{
        if (mm) {
                if (!ops->invalidate || !num_chunks)
                        return -EINVAL;
                mmgrab(mm);
        } else {
                /* No full SVM mode, only core drm_gpusvm_pages API. */
                if (ops || num_chunks || mm_range || notifier_size)
                        return -EINVAL;
        }

        gpusvm->name = name;
        gpusvm->drm = drm;
        gpusvm->mm = mm;
        gpusvm->mm_start = mm_start;
        gpusvm->mm_range = mm_range;
        gpusvm->notifier_size = notifier_size;
        gpusvm->ops = ops;
        gpusvm->chunk_sizes = chunk_sizes;
        gpusvm->num_chunks = num_chunks;

        gpusvm->root = RB_ROOT_CACHED;
        INIT_LIST_HEAD(&gpusvm->notifier_list);

        init_rwsem(&gpusvm->notifier_lock);

        fs_reclaim_acquire(GFP_KERNEL);
        might_lock(&gpusvm->notifier_lock);
        fs_reclaim_release(GFP_KERNEL);

#ifdef CONFIG_LOCKDEP
        gpusvm->lock_dep_map = NULL;
#endif

        return 0;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_init);

/**
 * to_drm_gpusvm_notifier() - retrieve the container struct for a given rbtree node
 * @node: a pointer to the rbtree node embedded within a drm_gpusvm_notifier struct
 *
 * Return: A pointer to the containing drm_gpusvm_notifier structure.
 */
static struct drm_gpusvm_notifier *to_drm_gpusvm_notifier(struct rb_node *node)
{
        return container_of(node, struct drm_gpusvm_notifier, itree.rb);
}

/**
 * drm_gpusvm_notifier_insert() - Insert GPU SVM notifier
 * @gpusvm: Pointer to the GPU SVM structure
 * @notifier: Pointer to the GPU SVM notifier structure
 *
 * This function inserts the GPU SVM notifier into the GPU SVM RB tree and list.
 */
static void drm_gpusvm_notifier_insert(struct drm_gpusvm *gpusvm,
                                       struct drm_gpusvm_notifier *notifier)
{
        struct rb_node *node;
        struct list_head *head;

        interval_tree_insert(&notifier->itree, &gpusvm->root);

        node = rb_prev(&notifier->itree.rb);
        if (node)
                head = &(to_drm_gpusvm_notifier(node))->entry;
        else
                head = &gpusvm->notifier_list;

        list_add(&notifier->entry, head);
}

/**
 * drm_gpusvm_notifier_remove() - Remove GPU SVM notifier
 * @gpusvm: Pointer to the GPU SVM tructure
 * @notifier: Pointer to the GPU SVM notifier structure
 *
 * This function removes the GPU SVM notifier from the GPU SVM RB tree and list.
 */
static void drm_gpusvm_notifier_remove(struct drm_gpusvm *gpusvm,
                                       struct drm_gpusvm_notifier *notifier)
{
        interval_tree_remove(&notifier->itree, &gpusvm->root);
        list_del(&notifier->entry);
}

/**
 * drm_gpusvm_fini() - Finalize the GPU SVM.
 * @gpusvm: Pointer to the GPU SVM structure.
 *
 * This function finalizes the GPU SVM by cleaning up any remaining ranges and
 * notifiers, and dropping a reference to struct MM.
 */
void drm_gpusvm_fini(struct drm_gpusvm *gpusvm)
{
        struct drm_gpusvm_notifier *notifier, *next;

        drm_gpusvm_for_each_notifier_safe(notifier, next, gpusvm, 0, LONG_MAX) {
                struct drm_gpusvm_range *range, *__next;

                /*
                 * Remove notifier first to avoid racing with any invalidation
                 */
                mmu_interval_notifier_remove(&notifier->notifier);
                notifier->flags.removed = true;

                drm_gpusvm_for_each_range_safe(range, __next, notifier, 0,
                                               LONG_MAX)
                        drm_gpusvm_range_remove(gpusvm, range);
        }

        if (gpusvm->mm)
                mmdrop(gpusvm->mm);
        WARN_ON(!RB_EMPTY_ROOT(&gpusvm->root.rb_root));
}
EXPORT_SYMBOL_GPL(drm_gpusvm_fini);

/**
 * drm_gpusvm_notifier_alloc() - Allocate GPU SVM notifier
 * @gpusvm: Pointer to the GPU SVM structure
 * @fault_addr: Fault address
 *
 * This function allocates and initializes the GPU SVM notifier structure.
 *
 * Return: Pointer to the allocated GPU SVM notifier on success, ERR_PTR() on failure.
 */
static struct drm_gpusvm_notifier *
drm_gpusvm_notifier_alloc(struct drm_gpusvm *gpusvm, unsigned long fault_addr)
{
        struct drm_gpusvm_notifier *notifier;

        if (gpusvm->ops->notifier_alloc)
                notifier = gpusvm->ops->notifier_alloc();
        else
                notifier = kzalloc_obj(*notifier);

        if (!notifier)
                return ERR_PTR(-ENOMEM);

        notifier->gpusvm = gpusvm;
        notifier->itree.start = ALIGN_DOWN(fault_addr, gpusvm->notifier_size);
        notifier->itree.last = ALIGN(fault_addr + 1, gpusvm->notifier_size) - 1;
        INIT_LIST_HEAD(&notifier->entry);
        notifier->root = RB_ROOT_CACHED;
        INIT_LIST_HEAD(&notifier->range_list);

        return notifier;
}

/**
 * drm_gpusvm_notifier_free() - Free GPU SVM notifier
 * @gpusvm: Pointer to the GPU SVM structure
 * @notifier: Pointer to the GPU SVM notifier structure
 *
 * This function frees the GPU SVM notifier structure.
 */
static void drm_gpusvm_notifier_free(struct drm_gpusvm *gpusvm,
                                     struct drm_gpusvm_notifier *notifier)
{
        WARN_ON(!RB_EMPTY_ROOT(&notifier->root.rb_root));

        if (gpusvm->ops->notifier_free)
                gpusvm->ops->notifier_free(notifier);
        else
                kfree(notifier);
}

/**
 * to_drm_gpusvm_range() - retrieve the container struct for a given rbtree node
 * @node: a pointer to the rbtree node embedded within a drm_gpusvm_range struct
 *
 * Return: A pointer to the containing drm_gpusvm_range structure.
 */
static struct drm_gpusvm_range *to_drm_gpusvm_range(struct rb_node *node)
{
        return container_of(node, struct drm_gpusvm_range, itree.rb);
}

/**
 * drm_gpusvm_range_insert() - Insert GPU SVM range
 * @notifier: Pointer to the GPU SVM notifier structure
 * @range: Pointer to the GPU SVM range structure
 *
 * This function inserts the GPU SVM range into the notifier RB tree and list.
 */
static void drm_gpusvm_range_insert(struct drm_gpusvm_notifier *notifier,
                                    struct drm_gpusvm_range *range)
{
        struct rb_node *node;
        struct list_head *head;

        drm_gpusvm_notifier_lock(notifier->gpusvm);
        interval_tree_insert(&range->itree, &notifier->root);

        node = rb_prev(&range->itree.rb);
        if (node)
                head = &(to_drm_gpusvm_range(node))->entry;
        else
                head = &notifier->range_list;

        list_add(&range->entry, head);
        drm_gpusvm_notifier_unlock(notifier->gpusvm);
}

/**
 * __drm_gpusvm_range_remove() - Remove GPU SVM range
 * @notifier: Pointer to the GPU SVM notifier structure
 * @range: Pointer to the GPU SVM range structure
 *
 * This macro removes the GPU SVM range from the notifier RB tree and list.
 */
static void __drm_gpusvm_range_remove(struct drm_gpusvm_notifier *notifier,
                                      struct drm_gpusvm_range *range)
{
        interval_tree_remove(&range->itree, &notifier->root);
        list_del(&range->entry);
}

/**
 * drm_gpusvm_range_alloc() - Allocate GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @notifier: Pointer to the GPU SVM notifier structure
 * @fault_addr: Fault address
 * @chunk_size: Chunk size
 * @migrate_devmem: Flag indicating whether to migrate device memory
 *
 * This function allocates and initializes the GPU SVM range structure.
 *
 * Return: Pointer to the allocated GPU SVM range on success, ERR_PTR() on failure.
 */
static struct drm_gpusvm_range *
drm_gpusvm_range_alloc(struct drm_gpusvm *gpusvm,
                       struct drm_gpusvm_notifier *notifier,
                       unsigned long fault_addr, unsigned long chunk_size,
                       bool migrate_devmem)
{
        struct drm_gpusvm_range *range;

        if (gpusvm->ops->range_alloc)
                range = gpusvm->ops->range_alloc(gpusvm);
        else
                range = kzalloc_obj(*range);

        if (!range)
                return ERR_PTR(-ENOMEM);

        kref_init(&range->refcount);
        range->gpusvm = gpusvm;
        range->notifier = notifier;
        range->itree.start = ALIGN_DOWN(fault_addr, chunk_size);
        range->itree.last = ALIGN(fault_addr + 1, chunk_size) - 1;
        INIT_LIST_HEAD(&range->entry);
        range->pages.notifier_seq = LONG_MAX;
        range->pages.flags.migrate_devmem = migrate_devmem ? 1 : 0;

        return range;
}

/**
 * drm_gpusvm_hmm_pfn_to_order() - Get the largest CPU mapping order.
 * @hmm_pfn: The current hmm_pfn.
 * @hmm_pfn_index: Index of the @hmm_pfn within the pfn array.
 * @npages: Number of pages within the pfn array i.e the hmm range size.
 *
 * To allow skipping PFNs with the same flags (like when they belong to
 * the same huge PTE) when looping over the pfn array, take a given a hmm_pfn,
 * and return the largest order that will fit inside the CPU PTE, but also
 * crucially accounting for the original hmm range boundaries.
 *
 * Return: The largest order that will safely fit within the size of the hmm_pfn
 * CPU PTE.
 */
static unsigned int drm_gpusvm_hmm_pfn_to_order(unsigned long hmm_pfn,
                                                unsigned long hmm_pfn_index,
                                                unsigned long npages)
{
        unsigned long size;

        size = 1UL << hmm_pfn_to_map_order(hmm_pfn);
        size -= (hmm_pfn & ~HMM_PFN_FLAGS) & (size - 1);
        hmm_pfn_index += size;
        if (hmm_pfn_index > npages)
                size -= (hmm_pfn_index - npages);

        return ilog2(size);
}

/**
 * drm_gpusvm_check_pages() - Check pages
 * @gpusvm: Pointer to the GPU SVM structure
 * @notifier: Pointer to the GPU SVM notifier structure
 * @start: Start address
 * @end: End address
 * @dev_private_owner: The device private page owner
 *
 * Check if pages between start and end have been faulted in on the CPU. Use to
 * prevent migration of pages without CPU backing store.
 *
 * Return: True if pages have been faulted into CPU, False otherwise
 */
static bool drm_gpusvm_check_pages(struct drm_gpusvm *gpusvm,
                                   struct drm_gpusvm_notifier *notifier,
                                   unsigned long start, unsigned long end,
                                   void *dev_private_owner)
{
        struct hmm_range hmm_range = {
                .default_flags = 0,
                .notifier = &notifier->notifier,
                .start = start,
                .end = end,
                .dev_private_owner = dev_private_owner,
        };
        unsigned long timeout =
                jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
        unsigned long *pfns;
        unsigned long npages = npages_in_range(start, end);
        int err, i;

        mmap_assert_locked(gpusvm->mm);

        pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
        if (!pfns)
                return false;

        hmm_range.notifier_seq = mmu_interval_read_begin(&notifier->notifier);
        hmm_range.hmm_pfns = pfns;

        while (true) {
                err = hmm_range_fault(&hmm_range);
                if (err == -EBUSY) {
                        if (time_after(jiffies, timeout))
                                break;

                        hmm_range.notifier_seq =
                                mmu_interval_read_begin(&notifier->notifier);
                        continue;
                }
                break;
        }
        if (err)
                goto err_free;

        for (i = 0; i < npages;) {
                if (!(pfns[i] & HMM_PFN_VALID)) {
                        err = -EFAULT;
                        goto err_free;
                }
                i += 0x1 << drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages);
        }

err_free:
        kvfree(pfns);
        return err ? false : true;
}

/**
 * drm_gpusvm_scan_mm() - Check the migration state of a drm_gpusvm_range
 * @range: Pointer to the struct drm_gpusvm_range to check.
 * @dev_private_owner: The struct dev_private_owner to use to determine
 * compatible device-private pages.
 * @pagemap: The struct dev_pagemap pointer to use for pagemap-specific
 * checks.
 *
 * Scan the CPU address space corresponding to @range and return the
 * current migration state. Note that the result may be invalid as
 * soon as the function returns. It's an advisory check.
 *
 * TODO: Bail early and call hmm_range_fault() for subranges.
 *
 * Return: See &enum drm_gpusvm_scan_result.
 */
enum drm_gpusvm_scan_result drm_gpusvm_scan_mm(struct drm_gpusvm_range *range,
                                               void *dev_private_owner,
                                               const struct dev_pagemap *pagemap)
{
        struct mmu_interval_notifier *notifier = &range->notifier->notifier;
        unsigned long start = drm_gpusvm_range_start(range);
        unsigned long end = drm_gpusvm_range_end(range);
        struct hmm_range hmm_range = {
                .default_flags = 0,
                .notifier = notifier,
                .start = start,
                .end = end,
                .dev_private_owner = dev_private_owner,
        };
        unsigned long timeout =
                jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
        enum drm_gpusvm_scan_result state = DRM_GPUSVM_SCAN_UNPOPULATED, new_state;
        unsigned long *pfns;
        unsigned long npages = npages_in_range(start, end);
        const struct dev_pagemap *other = NULL;
        int err, i;

        pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
        if (!pfns)
                return DRM_GPUSVM_SCAN_UNPOPULATED;

        hmm_range.hmm_pfns = pfns;

retry:
        hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
        mmap_read_lock(range->gpusvm->mm);

        while (true) {
                err = hmm_range_fault(&hmm_range);
                if (err == -EBUSY) {
                        if (time_after(jiffies, timeout))
                                break;

                        hmm_range.notifier_seq =
                                mmu_interval_read_begin(notifier);
                        continue;
                }
                break;
        }
        mmap_read_unlock(range->gpusvm->mm);
        if (err)
                goto err_free;

        drm_gpusvm_notifier_lock(range->gpusvm);
        if (mmu_interval_read_retry(notifier, hmm_range.notifier_seq)) {
                drm_gpusvm_notifier_unlock(range->gpusvm);
                goto retry;
        }

        for (i = 0; i < npages;) {
                struct page *page;
                const struct dev_pagemap *cur = NULL;

                if (!(pfns[i] & HMM_PFN_VALID)) {
                        state = DRM_GPUSVM_SCAN_UNPOPULATED;
                        goto err_free;
                }

                page = hmm_pfn_to_page(pfns[i]);
                if (is_device_private_page(page) ||
                    is_device_coherent_page(page))
                        cur = page_pgmap(page);

                if (cur == pagemap) {
                        new_state = DRM_GPUSVM_SCAN_EQUAL;
                } else if (cur && (cur == other || !other)) {
                        new_state = DRM_GPUSVM_SCAN_OTHER;
                        other = cur;
                } else if (cur) {
                        new_state = DRM_GPUSVM_SCAN_MIXED_DEVICE;
                } else {
                        new_state = DRM_GPUSVM_SCAN_SYSTEM;
                }

                /*
                 * TODO: Could use an array for state
                 * transitions, and caller might want it
                 * to bail early for some results.
                 */
                if (state == DRM_GPUSVM_SCAN_UNPOPULATED) {
                        state = new_state;
                } else if (state != new_state) {
                        if (new_state == DRM_GPUSVM_SCAN_SYSTEM ||
                            state == DRM_GPUSVM_SCAN_SYSTEM)
                                state = DRM_GPUSVM_SCAN_MIXED;
                        else if (state != DRM_GPUSVM_SCAN_MIXED)
                                state = DRM_GPUSVM_SCAN_MIXED_DEVICE;
                }

                i += 1ul << drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages);
        }

err_free:
        drm_gpusvm_notifier_unlock(range->gpusvm);

        kvfree(pfns);
        return state;
}
EXPORT_SYMBOL(drm_gpusvm_scan_mm);

/**
 * drm_gpusvm_range_chunk_size() - Determine chunk size for GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @notifier: Pointer to the GPU SVM notifier structure
 * @vas: Pointer to the virtual memory area structure
 * @fault_addr: Fault address
 * @gpuva_start: Start address of GPUVA which mirrors CPU
 * @gpuva_end: End address of GPUVA which mirrors CPU
 * @check_pages_threshold: Check CPU pages for present threshold
 * @dev_private_owner: The device private page owner
 *
 * This function determines the chunk size for the GPU SVM range based on the
 * fault address, GPU SVM chunk sizes, existing GPU SVM ranges, and the virtual
 * memory area boundaries.
 *
 * Return: Chunk size on success, LONG_MAX on failure.
 */
static unsigned long
drm_gpusvm_range_chunk_size(struct drm_gpusvm *gpusvm,
                            struct drm_gpusvm_notifier *notifier,
                            struct vm_area_struct *vas,
                            unsigned long fault_addr,
                            unsigned long gpuva_start,
                            unsigned long gpuva_end,
                            unsigned long check_pages_threshold,
                            void *dev_private_owner)
{
        unsigned long start, end;
        int i = 0;

retry:
        for (; i < gpusvm->num_chunks; ++i) {
                start = ALIGN_DOWN(fault_addr, gpusvm->chunk_sizes[i]);
                end = ALIGN(fault_addr + 1, gpusvm->chunk_sizes[i]);

                if (start >= vas->vm_start && end <= vas->vm_end &&
                    start >= drm_gpusvm_notifier_start(notifier) &&
                    end <= drm_gpusvm_notifier_end(notifier) &&
                    start >= gpuva_start && end <= gpuva_end)
                        break;
        }

        if (i == gpusvm->num_chunks)
                return LONG_MAX;

        /*
         * If allocation more than page, ensure not to overlap with existing
         * ranges.
         */
        if (end - start != SZ_4K) {
                struct drm_gpusvm_range *range;

                range = drm_gpusvm_range_find(notifier, start, end);
                if (range) {
                        ++i;
                        goto retry;
                }

                /*
                 * XXX: Only create range on pages CPU has faulted in. Without
                 * this check, or prefault, on BMG 'xe_exec_system_allocator --r
                 * process-many-malloc' fails. In the failure case, each process
                 * mallocs 16k but the CPU VMA is ~128k which results in 64k SVM
                 * ranges. When migrating the SVM ranges, some processes fail in
                 * drm_pagemap_migrate_to_devmem with 'migrate.cpages != npages'
                 * and then upon drm_gpusvm_range_get_pages device pages from
                 * other processes are collected + faulted in which creates all
                 * sorts of problems. Unsure exactly how this happening, also
                 * problem goes away if 'xe_exec_system_allocator --r
                 * process-many-malloc' mallocs at least 64k at a time.
                 */
                if (end - start <= check_pages_threshold &&
                    !drm_gpusvm_check_pages(gpusvm, notifier, start, end, dev_private_owner)) {
                        ++i;
                        goto retry;
                }
        }

        return end - start;
}

#ifdef CONFIG_LOCKDEP
/**
 * drm_gpusvm_driver_lock_held() - Assert GPU SVM driver lock is held
 * @gpusvm: Pointer to the GPU SVM structure.
 *
 * Ensure driver lock is held.
 */
static void drm_gpusvm_driver_lock_held(struct drm_gpusvm *gpusvm)
{
        if ((gpusvm)->lock_dep_map)
                lockdep_assert(lock_is_held_type((gpusvm)->lock_dep_map, 0));
}
#else
static void drm_gpusvm_driver_lock_held(struct drm_gpusvm *gpusvm)
{
}
#endif

/**
 * drm_gpusvm_find_vma_start() - Find start address for first VMA in range
 * @gpusvm: Pointer to the GPU SVM structure
 * @start: The inclusive start user address.
 * @end: The exclusive end user address.
 *
 * Returns: The start address of first VMA within the provided range,
 * ULONG_MAX otherwise. Assumes start_addr < end_addr.
 */
unsigned long
drm_gpusvm_find_vma_start(struct drm_gpusvm *gpusvm,
                          unsigned long start,
                          unsigned long end)
{
        struct mm_struct *mm = gpusvm->mm;
        struct vm_area_struct *vma;
        unsigned long addr = ULONG_MAX;

        if (!mmget_not_zero(mm))
                return addr;

        mmap_read_lock(mm);

        vma = find_vma_intersection(mm, start, end);
        if (vma)
                addr =  vma->vm_start;

        mmap_read_unlock(mm);
        mmput(mm);

        return addr;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_find_vma_start);

/**
 * drm_gpusvm_range_find_or_insert() - Find or insert GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @fault_addr: Fault address
 * @gpuva_start: Start address of GPUVA which mirrors CPU
 * @gpuva_end: End address of GPUVA which mirrors CPU
 * @ctx: GPU SVM context
 *
 * This function finds or inserts a newly allocated a GPU SVM range based on the
 * fault address. Caller must hold a lock to protect range lookup and insertion.
 *
 * Return: Pointer to the GPU SVM range on success, ERR_PTR() on failure.
 */
struct drm_gpusvm_range *
drm_gpusvm_range_find_or_insert(struct drm_gpusvm *gpusvm,
                                unsigned long fault_addr,
                                unsigned long gpuva_start,
                                unsigned long gpuva_end,
                                const struct drm_gpusvm_ctx *ctx)
{
        struct drm_gpusvm_notifier *notifier;
        struct drm_gpusvm_range *range;
        struct mm_struct *mm = gpusvm->mm;
        struct vm_area_struct *vas;
        bool notifier_alloc = false;
        unsigned long chunk_size;
        int err;
        bool migrate_devmem;

        drm_gpusvm_driver_lock_held(gpusvm);

        if (fault_addr < gpusvm->mm_start ||
            fault_addr > gpusvm->mm_start + gpusvm->mm_range)
                return ERR_PTR(-EINVAL);

        if (!mmget_not_zero(mm))
                return ERR_PTR(-EFAULT);

        notifier = drm_gpusvm_notifier_find(gpusvm, fault_addr, fault_addr + 1);
        if (!notifier) {
                notifier = drm_gpusvm_notifier_alloc(gpusvm, fault_addr);
                if (IS_ERR(notifier)) {
                        err = PTR_ERR(notifier);
                        goto err_mmunlock;
                }
                notifier_alloc = true;
                err = mmu_interval_notifier_insert(&notifier->notifier,
                                                   mm,
                                                   drm_gpusvm_notifier_start(notifier),
                                                   drm_gpusvm_notifier_size(notifier),
                                                   &drm_gpusvm_notifier_ops);
                if (err)
                        goto err_notifier;
        }

        mmap_read_lock(mm);

        vas = vma_lookup(mm, fault_addr);
        if (!vas) {
                err = -ENOENT;
                goto err_notifier_remove;
        }

        if (!ctx->read_only && !(vas->vm_flags & VM_WRITE)) {
                err = -EPERM;
                goto err_notifier_remove;
        }

        range = drm_gpusvm_range_find(notifier, fault_addr, fault_addr + 1);
        if (range)
                goto out_mmunlock;
        /*
         * XXX: Short-circuiting migration based on migrate_vma_* current
         * limitations. If/when migrate_vma_* add more support, this logic will
         * have to change.
         */
        migrate_devmem = ctx->devmem_possible &&
                vma_is_anonymous(vas) && !is_vm_hugetlb_page(vas);

        chunk_size = drm_gpusvm_range_chunk_size(gpusvm, notifier, vas,
                                                 fault_addr, gpuva_start,
                                                 gpuva_end,
                                                 ctx->check_pages_threshold,
                                                 ctx->device_private_page_owner);
        if (chunk_size == LONG_MAX) {
                err = -EINVAL;
                goto err_notifier_remove;
        }

        range = drm_gpusvm_range_alloc(gpusvm, notifier, fault_addr, chunk_size,
                                       migrate_devmem);
        if (IS_ERR(range)) {
                err = PTR_ERR(range);
                goto err_notifier_remove;
        }

        drm_gpusvm_range_insert(notifier, range);
        if (notifier_alloc)
                drm_gpusvm_notifier_insert(gpusvm, notifier);

out_mmunlock:
        mmap_read_unlock(mm);
        mmput(mm);

        return range;

err_notifier_remove:
        mmap_read_unlock(mm);
        if (notifier_alloc)
                mmu_interval_notifier_remove(&notifier->notifier);
err_notifier:
        if (notifier_alloc)
                drm_gpusvm_notifier_free(gpusvm, notifier);
err_mmunlock:
        mmput(mm);
        return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_find_or_insert);

/**
 * __drm_gpusvm_unmap_pages() - Unmap pages associated with GPU SVM pages (internal)
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 * @npages: Number of pages to unmap
 *
 * This function unmap pages associated with a GPU SVM pages struct. Assumes and
 * asserts correct locking is in place when called.
 */
static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
                                     struct drm_gpusvm_pages *svm_pages,
                                     unsigned long npages)
{
        struct drm_pagemap *dpagemap = svm_pages->dpagemap;
        struct device *dev = gpusvm->drm->dev;
        unsigned long i, j;

        lockdep_assert_held(&gpusvm->notifier_lock);

        if (svm_pages->flags.has_dma_mapping) {
                struct drm_gpusvm_pages_flags flags = {
                        .__flags = svm_pages->flags.__flags,
                };

                for (i = 0, j = 0; i < npages; j++) {
                        struct drm_pagemap_addr *addr = &svm_pages->dma_addr[j];

                        if (addr->proto == DRM_INTERCONNECT_SYSTEM)
                                dma_unmap_page(dev,
                                               addr->addr,
                                               PAGE_SIZE << addr->order,
                                               addr->dir);
                        else if (dpagemap && dpagemap->ops->device_unmap)
                                dpagemap->ops->device_unmap(dpagemap,
                                                            dev, addr);
                        i += 1 << addr->order;
                }

                /* WRITE_ONCE pairs with READ_ONCE for opportunistic checks */
                flags.has_devmem_pages = false;
                flags.has_dma_mapping = false;
                WRITE_ONCE(svm_pages->flags.__flags, flags.__flags);

                drm_pagemap_put(svm_pages->dpagemap);
                svm_pages->dpagemap = NULL;
        }
}

/**
 * __drm_gpusvm_free_pages() - Free dma array associated with GPU SVM pages
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 *
 * This function frees the dma address array associated with a GPU SVM range.
 */
static void __drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm,
                                    struct drm_gpusvm_pages *svm_pages)
{
        lockdep_assert_held(&gpusvm->notifier_lock);

        if (svm_pages->dma_addr) {
                kvfree(svm_pages->dma_addr);
                svm_pages->dma_addr = NULL;
        }
}

/**
 * drm_gpusvm_free_pages() - Free dma-mapping associated with GPU SVM pages
 * struct
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 * @npages: Number of mapped pages
 *
 * This function unmaps and frees the dma address array associated with a GPU
 * SVM pages struct.
 */
void drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm,
                           struct drm_gpusvm_pages *svm_pages,
                           unsigned long npages)
{
        drm_gpusvm_notifier_lock(gpusvm);
        __drm_gpusvm_unmap_pages(gpusvm, svm_pages, npages);
        __drm_gpusvm_free_pages(gpusvm, svm_pages);
        drm_gpusvm_notifier_unlock(gpusvm);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_free_pages);

/**
 * drm_gpusvm_range_remove() - Remove GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @range: Pointer to the GPU SVM range to be removed
 *
 * This function removes the specified GPU SVM range and also removes the parent
 * GPU SVM notifier if no more ranges remain in the notifier. The caller must
 * hold a lock to protect range and notifier removal.
 */
void drm_gpusvm_range_remove(struct drm_gpusvm *gpusvm,
                             struct drm_gpusvm_range *range)
{
        unsigned long npages = npages_in_range(drm_gpusvm_range_start(range),
                                               drm_gpusvm_range_end(range));
        struct drm_gpusvm_notifier *notifier;

        drm_gpusvm_driver_lock_held(gpusvm);

        notifier = drm_gpusvm_notifier_find(gpusvm,
                                            drm_gpusvm_range_start(range),
                                            drm_gpusvm_range_start(range) + 1);
        if (WARN_ON_ONCE(!notifier))
                return;

        drm_gpusvm_notifier_lock(gpusvm);
        __drm_gpusvm_unmap_pages(gpusvm, &range->pages, npages);
        __drm_gpusvm_free_pages(gpusvm, &range->pages);
        __drm_gpusvm_range_remove(notifier, range);
        drm_gpusvm_notifier_unlock(gpusvm);

        drm_gpusvm_range_put(range);

        if (RB_EMPTY_ROOT(&notifier->root.rb_root)) {
                if (!notifier->flags.removed)
                        mmu_interval_notifier_remove(&notifier->notifier);
                drm_gpusvm_notifier_remove(gpusvm, notifier);
                drm_gpusvm_notifier_free(gpusvm, notifier);
        }
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_remove);

/**
 * drm_gpusvm_range_get() - Get a reference to GPU SVM range
 * @range: Pointer to the GPU SVM range
 *
 * This function increments the reference count of the specified GPU SVM range.
 *
 * Return: Pointer to the GPU SVM range.
 */
struct drm_gpusvm_range *
drm_gpusvm_range_get(struct drm_gpusvm_range *range)
{
        kref_get(&range->refcount);

        return range;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_get);

/**
 * drm_gpusvm_range_destroy() - Destroy GPU SVM range
 * @refcount: Pointer to the reference counter embedded in the GPU SVM range
 *
 * This function destroys the specified GPU SVM range when its reference count
 * reaches zero. If a custom range-free function is provided, it is invoked to
 * free the range; otherwise, the range is deallocated using kfree().
 */
static void drm_gpusvm_range_destroy(struct kref *refcount)
{
        struct drm_gpusvm_range *range =
                container_of(refcount, struct drm_gpusvm_range, refcount);
        struct drm_gpusvm *gpusvm = range->gpusvm;

        if (gpusvm->ops->range_free)
                gpusvm->ops->range_free(range);
        else
                kfree(range);
}

/**
 * drm_gpusvm_range_put() - Put a reference to GPU SVM range
 * @range: Pointer to the GPU SVM range
 *
 * This function decrements the reference count of the specified GPU SVM range
 * and frees it when the count reaches zero.
 */
void drm_gpusvm_range_put(struct drm_gpusvm_range *range)
{
        kref_put(&range->refcount, drm_gpusvm_range_destroy);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_put);

/**
 * drm_gpusvm_pages_valid() - GPU SVM range pages valid
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 *
 * This function determines if a GPU SVM range pages are valid. Expected be
 * called holding gpusvm->notifier_lock and as the last step before committing a
 * GPU binding. This is akin to a notifier seqno check in the HMM documentation
 * but due to wider notifiers (i.e., notifiers which span multiple ranges) this
 * function is required for finer grained checking (i.e., per range) if pages
 * are valid.
 *
 * Return: True if GPU SVM range has valid pages, False otherwise
 */
static bool drm_gpusvm_pages_valid(struct drm_gpusvm *gpusvm,
                                   struct drm_gpusvm_pages *svm_pages)
{
        lockdep_assert_held(&gpusvm->notifier_lock);

        return svm_pages->flags.has_devmem_pages || svm_pages->flags.has_dma_mapping;
}

/**
 * drm_gpusvm_range_pages_valid() - GPU SVM range pages valid
 * @gpusvm: Pointer to the GPU SVM structure
 * @range: Pointer to the GPU SVM range structure
 *
 * This function determines if a GPU SVM range pages are valid. Expected be
 * called holding gpusvm->notifier_lock and as the last step before committing a
 * GPU binding. This is akin to a notifier seqno check in the HMM documentation
 * but due to wider notifiers (i.e., notifiers which span multiple ranges) this
 * function is required for finer grained checking (i.e., per range) if pages
 * are valid.
 *
 * Return: True if GPU SVM range has valid pages, False otherwise
 */
bool drm_gpusvm_range_pages_valid(struct drm_gpusvm *gpusvm,
                                  struct drm_gpusvm_range *range)
{
        return drm_gpusvm_pages_valid(gpusvm, &range->pages);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_pages_valid);

/**
 * drm_gpusvm_pages_valid_unlocked() - GPU SVM pages valid unlocked
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 *
 * This function determines if a GPU SVM pages are valid. Expected be called
 * without holding gpusvm->notifier_lock.
 *
 * Return: True if GPU SVM pages are valid, False otherwise
 */
static bool drm_gpusvm_pages_valid_unlocked(struct drm_gpusvm *gpusvm,
                                            struct drm_gpusvm_pages *svm_pages)
{
        bool pages_valid;

        if (!svm_pages->dma_addr)
                return false;

        drm_gpusvm_notifier_lock(gpusvm);
        pages_valid = drm_gpusvm_pages_valid(gpusvm, svm_pages);
        if (!pages_valid)
                __drm_gpusvm_free_pages(gpusvm, svm_pages);
        drm_gpusvm_notifier_unlock(gpusvm);

        return pages_valid;
}

/**
 * drm_gpusvm_get_pages() - Get pages and populate GPU SVM pages struct
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: The SVM pages to populate. This will contain the dma-addresses
 * @mm: The mm corresponding to the CPU range
 * @notifier: The corresponding notifier for the given CPU range
 * @pages_start: Start CPU address for the pages
 * @pages_end: End CPU address for the pages (exclusive)
 * @ctx: GPU SVM context
 *
 * This function gets and maps pages for CPU range and ensures they are
 * mapped for DMA access.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
                         struct drm_gpusvm_pages *svm_pages,
                         struct mm_struct *mm,
                         struct mmu_interval_notifier *notifier,
                         unsigned long pages_start, unsigned long pages_end,
                         const struct drm_gpusvm_ctx *ctx)
{
        struct hmm_range hmm_range = {
                .default_flags = HMM_PFN_REQ_FAULT | (ctx->read_only ? 0 :
                        HMM_PFN_REQ_WRITE),
                .notifier = notifier,
                .start = pages_start,
                .end = pages_end,
                .dev_private_owner = ctx->device_private_page_owner,
        };
        void *zdd;
        unsigned long timeout =
                jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
        unsigned long i, j;
        unsigned long npages = npages_in_range(pages_start, pages_end);
        unsigned long num_dma_mapped;
        unsigned int order = 0;
        unsigned long *pfns;
        int err = 0;
        struct dev_pagemap *pagemap;
        struct drm_pagemap *dpagemap;
        struct drm_gpusvm_pages_flags flags;
        enum dma_data_direction dma_dir = ctx->read_only ? DMA_TO_DEVICE :
                                                           DMA_BIDIRECTIONAL;

retry:
        if (time_after(jiffies, timeout))
                return -EBUSY;

        hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
        if (drm_gpusvm_pages_valid_unlocked(gpusvm, svm_pages))
                goto set_seqno;

        pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
        if (!pfns)
                return -ENOMEM;

        if (!mmget_not_zero(mm)) {
                err = -EFAULT;
                goto err_free;
        }

        hmm_range.hmm_pfns = pfns;
        while (true) {
                mmap_read_lock(mm);
                err = hmm_range_fault(&hmm_range);
                mmap_read_unlock(mm);

                if (err == -EBUSY) {
                        if (time_after(jiffies, timeout))
                                break;

                        hmm_range.notifier_seq =
                                mmu_interval_read_begin(notifier);
                        continue;
                }
                break;
        }
        mmput(mm);
        if (err)
                goto err_free;

map_pages:
        /*
         * Perform all dma mappings under the notifier lock to not
         * access freed pages. A notifier will either block on
         * the notifier lock or unmap dma.
         */
        drm_gpusvm_notifier_lock(gpusvm);

        flags.__flags = svm_pages->flags.__flags;
        if (flags.unmapped) {
                drm_gpusvm_notifier_unlock(gpusvm);
                err = -EFAULT;
                goto err_free;
        }

        if (mmu_interval_read_retry(notifier, hmm_range.notifier_seq)) {
                drm_gpusvm_notifier_unlock(gpusvm);
                kvfree(pfns);
                goto retry;
        }

        if (!svm_pages->dma_addr) {
                /* Unlock and restart mapping to allocate memory. */
                drm_gpusvm_notifier_unlock(gpusvm);
                svm_pages->dma_addr =
                        kvmalloc_objs(*svm_pages->dma_addr, npages);
                if (!svm_pages->dma_addr) {
                        err = -ENOMEM;
                        goto err_free;
                }
                goto map_pages;
        }

        zdd = NULL;
        pagemap = NULL;
        num_dma_mapped = 0;
        for (i = 0, j = 0; i < npages; ++j) {
                struct page *page = hmm_pfn_to_page(pfns[i]);

                order = drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages);
                if (is_device_private_page(page) ||
                    is_device_coherent_page(page)) {
                        if (!ctx->allow_mixed &&
                            zdd != page->zone_device_data && i > 0) {
                                err = -EOPNOTSUPP;
                                goto err_unmap;
                        }
                        zdd = page->zone_device_data;
                        if (pagemap != page_pgmap(page)) {
                                if (i > 0) {
                                        err = -EOPNOTSUPP;
                                        goto err_unmap;
                                }

                                pagemap = page_pgmap(page);
                                dpagemap = drm_pagemap_page_to_dpagemap(page);
                                if (drm_WARN_ON(gpusvm->drm, !dpagemap)) {
                                        /*
                                         * Raced. This is not supposed to happen
                                         * since hmm_range_fault() should've migrated
                                         * this page to system.
                                         */
                                        err = -EAGAIN;
                                        goto err_unmap;
                                }
                        }
                        svm_pages->dma_addr[j] =
                                dpagemap->ops->device_map(dpagemap,
                                                          gpusvm->drm->dev,
                                                          page, order,
                                                          dma_dir);
                        if (dma_mapping_error(gpusvm->drm->dev,
                                              svm_pages->dma_addr[j].addr)) {
                                err = -EFAULT;
                                goto err_unmap;
                        }
                } else {
                        dma_addr_t addr;

                        if (is_zone_device_page(page) ||
                            (pagemap && !ctx->allow_mixed)) {
                                err = -EOPNOTSUPP;
                                goto err_unmap;
                        }

                        if (ctx->devmem_only) {
                                err = -EFAULT;
                                goto err_unmap;
                        }

                        addr = dma_map_page(gpusvm->drm->dev,
                                            page, 0,
                                            PAGE_SIZE << order,
                                            dma_dir);
                        if (dma_mapping_error(gpusvm->drm->dev, addr)) {
                                err = -EFAULT;
                                goto err_unmap;
                        }

                        svm_pages->dma_addr[j] = drm_pagemap_addr_encode
                                (addr, DRM_INTERCONNECT_SYSTEM, order,
                                 dma_dir);
                }
                i += 1 << order;
                num_dma_mapped = i;
                flags.has_dma_mapping = true;
        }

        if (pagemap) {
                flags.has_devmem_pages = true;
                drm_pagemap_get(dpagemap);
                drm_pagemap_put(svm_pages->dpagemap);
                svm_pages->dpagemap = dpagemap;
        }

        /* WRITE_ONCE pairs with READ_ONCE for opportunistic checks */
        WRITE_ONCE(svm_pages->flags.__flags, flags.__flags);

        drm_gpusvm_notifier_unlock(gpusvm);
        kvfree(pfns);
set_seqno:
        svm_pages->notifier_seq = hmm_range.notifier_seq;

        return 0;

err_unmap:
        __drm_gpusvm_unmap_pages(gpusvm, svm_pages, num_dma_mapped);
        drm_gpusvm_notifier_unlock(gpusvm);
err_free:
        kvfree(pfns);
        if (err == -EAGAIN)
                goto retry;
        return err;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_get_pages);

/**
 * drm_gpusvm_range_get_pages() - Get pages for a GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @range: Pointer to the GPU SVM range structure
 * @ctx: GPU SVM context
 *
 * This function gets pages for a GPU SVM range and ensures they are mapped for
 * DMA access.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_gpusvm_range_get_pages(struct drm_gpusvm *gpusvm,
                               struct drm_gpusvm_range *range,
                               const struct drm_gpusvm_ctx *ctx)
{
        return drm_gpusvm_get_pages(gpusvm, &range->pages, gpusvm->mm,
                                    &range->notifier->notifier,
                                    drm_gpusvm_range_start(range),
                                    drm_gpusvm_range_end(range), ctx);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_get_pages);

/**
 * drm_gpusvm_unmap_pages() - Unmap GPU svm pages
 * @gpusvm: Pointer to the GPU SVM structure
 * @svm_pages: Pointer to the GPU SVM pages structure
 * @npages: Number of pages in @svm_pages.
 * @ctx: GPU SVM context
 *
 * This function unmaps pages associated with a GPU SVM pages struct. If
 * @in_notifier is set, it is assumed that gpusvm->notifier_lock is held in
 * write mode; if it is clear, it acquires gpusvm->notifier_lock in read mode.
 * Must be called in the invalidate() callback of the corresponding notifier for
 * IOMMU security model.
 */
void drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
                            struct drm_gpusvm_pages *svm_pages,
                            unsigned long npages,
                            const struct drm_gpusvm_ctx *ctx)
{
        if (ctx->in_notifier)
                lockdep_assert_held_write(&gpusvm->notifier_lock);
        else
                drm_gpusvm_notifier_lock(gpusvm);

        __drm_gpusvm_unmap_pages(gpusvm, svm_pages, npages);

        if (!ctx->in_notifier)
                drm_gpusvm_notifier_unlock(gpusvm);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_unmap_pages);

/**
 * drm_gpusvm_range_unmap_pages() - Unmap pages associated with a GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @range: Pointer to the GPU SVM range structure
 * @ctx: GPU SVM context
 *
 * This function unmaps pages associated with a GPU SVM range. If @in_notifier
 * is set, it is assumed that gpusvm->notifier_lock is held in write mode; if it
 * is clear, it acquires gpusvm->notifier_lock in read mode. Must be called on
 * each GPU SVM range attached to notifier in gpusvm->ops->invalidate for IOMMU
 * security model.
 */
void drm_gpusvm_range_unmap_pages(struct drm_gpusvm *gpusvm,
                                  struct drm_gpusvm_range *range,
                                  const struct drm_gpusvm_ctx *ctx)
{
        unsigned long npages = npages_in_range(drm_gpusvm_range_start(range),
                                               drm_gpusvm_range_end(range));

        return drm_gpusvm_unmap_pages(gpusvm, &range->pages, npages, ctx);
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_unmap_pages);

/**
 * drm_gpusvm_range_evict() - Evict GPU SVM range
 * @gpusvm: Pointer to the GPU SVM structure
 * @range: Pointer to the GPU SVM range to be removed
 *
 * This function evicts the specified GPU SVM range.
 *
 * Return: 0 on success, a negative error code on failure.
 */
int drm_gpusvm_range_evict(struct drm_gpusvm *gpusvm,
                           struct drm_gpusvm_range *range)
{
        struct mmu_interval_notifier *notifier = &range->notifier->notifier;
        struct hmm_range hmm_range = {
                .default_flags = HMM_PFN_REQ_FAULT,
                .notifier = notifier,
                .start = drm_gpusvm_range_start(range),
                .end = drm_gpusvm_range_end(range),
                .dev_private_owner = NULL,
        };
        unsigned long timeout =
                jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
        unsigned long *pfns;
        unsigned long npages = npages_in_range(drm_gpusvm_range_start(range),
                                               drm_gpusvm_range_end(range));
        int err = 0;
        struct mm_struct *mm = gpusvm->mm;

        if (!mmget_not_zero(mm))
                return -EFAULT;

        pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
        if (!pfns)
                return -ENOMEM;

        hmm_range.hmm_pfns = pfns;
        while (!time_after(jiffies, timeout)) {
                hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
                if (time_after(jiffies, timeout)) {
                        err = -ETIME;
                        break;
                }

                mmap_read_lock(mm);
                err = hmm_range_fault(&hmm_range);
                mmap_read_unlock(mm);
                if (err != -EBUSY)
                        break;
        }

        kvfree(pfns);
        mmput(mm);

        return err;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_evict);

/**
 * drm_gpusvm_has_mapping() - Check if GPU SVM has mapping for the given address range
 * @gpusvm: Pointer to the GPU SVM structure.
 * @start: Start address
 * @end: End address
 *
 * Return: True if GPU SVM has mapping, False otherwise
 */
bool drm_gpusvm_has_mapping(struct drm_gpusvm *gpusvm, unsigned long start,
                            unsigned long end)
{
        struct drm_gpusvm_notifier *notifier;

        drm_gpusvm_for_each_notifier(notifier, gpusvm, start, end) {
                struct drm_gpusvm_range *range = NULL;

                drm_gpusvm_for_each_range(range, notifier, start, end)
                        return true;
        }

        return false;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_has_mapping);

/**
 * drm_gpusvm_range_set_unmapped() - Mark a GPU SVM range as unmapped
 * @range: Pointer to the GPU SVM range structure.
 * @mmu_range: Pointer to the MMU notifier range structure.
 *
 * This function marks a GPU SVM range as unmapped and sets the partial_unmap flag
 * if the range partially falls within the provided MMU notifier range.
 */
void drm_gpusvm_range_set_unmapped(struct drm_gpusvm_range *range,
                                   const struct mmu_notifier_range *mmu_range)
{
        lockdep_assert_held_write(&range->gpusvm->notifier_lock);

        range->pages.flags.unmapped = true;
        if (drm_gpusvm_range_start(range) < mmu_range->start ||
            drm_gpusvm_range_end(range) > mmu_range->end)
                range->pages.flags.partial_unmap = true;
}
EXPORT_SYMBOL_GPL(drm_gpusvm_range_set_unmapped);

MODULE_DESCRIPTION("DRM GPUSVM");
MODULE_LICENSE("GPL");