// SPDX-License-Identifier: GPL-2.0-only OR MIT
/*
 * Copyright © 2024-2025 Intel Corporation
 */

#include <linux/dma-fence.h>
#include <linux/dma-mapping.h>
#include <linux/migrate.h>
#include <linux/pagemap.h>
#include <drm/drm_drv.h>
#include <drm/drm_pagemap.h>
#include <drm/drm_pagemap_util.h>
#include <drm/drm_print.h>

/**
 * DOC: Overview
 *
 * The DRM pagemap layer is intended to augment the dev_pagemap functionality by
 * providing a way to populate a struct mm_struct virtual range with device
 * private pages and to provide helpers to abstract device memory allocations,
 * to migrate memory back and forth between device memory and system RAM and
 * to handle access (and in the future migration) between devices implementing
 * a fast interconnect that is not necessarily visible to the rest of the
 * system.
 *
 * Typically the DRM pagemap receives requests from one or more DRM GPU SVM
 * instances to populate struct mm_struct virtual ranges with memory, and the
 * migration is best effort only and may thus fail. The implementation should
 * also handle device unbinding by blocking (return an -ENODEV) error for new
 * population requests and after that migrate all device pages to system ram.
 */

/**
 * DOC: Migration
 *
 * Migration granularity typically follows the GPU SVM range requests, but
 * if there are clashes, due to races or due to the fact that multiple GPU
 * SVM instances have different views of the ranges used, and because of that
 * parts of a requested range is already present in the requested device memory,
 * the implementation has a variety of options. It can fail and it can choose
 * to populate only the part of the range that isn't already in device memory,
 * and it can evict the range to system before trying to migrate. Ideally an
 * implementation would just try to migrate the missing part of the range and
 * allocate just enough memory to do so.
 *
 * When migrating to system memory as a response to a cpu fault or a device
 * memory eviction request, currently a full device memory allocation is
 * migrated back to system. Moving forward this might need improvement for
 * situations where a single page needs bouncing between system memory and
 * device memory due to, for example, atomic operations.
 *
 * Key DRM pagemap components:
 *
 * - Device Memory Allocations:
 *      Embedded structure containing enough information for the drm_pagemap 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.
 */

/**
 * struct drm_pagemap_zdd - GPU SVM zone device data
 *
 * @refcount: Reference count for the zdd
 * @devmem_allocation: device memory allocation
 * @dpagemap: Refcounted pointer to the underlying struct drm_pagemap.
 *
 * This structure serves as a generic wrapper installed in
 * page->zone_device_data. It provides infrastructure for looking up a device
 * memory allocation upon CPU page fault and asynchronously releasing device
 * memory once the CPU has no page references. Asynchronous release is useful
 * because CPU page references can be dropped in IRQ contexts, while releasing
 * device memory likely requires sleeping locks.
 */
struct drm_pagemap_zdd {
        struct kref refcount;
        struct drm_pagemap_devmem *devmem_allocation;
        struct drm_pagemap *dpagemap;
};

/**
 * drm_pagemap_zdd_alloc() - Allocate a zdd structure.
 * @dpagemap: Pointer to the underlying struct drm_pagemap.
 *
 * This function allocates and initializes a new zdd structure. It sets up the
 * reference count and initializes the destroy work.
 *
 * Return: Pointer to the allocated zdd on success, ERR_PTR() on failure.
 */
static struct drm_pagemap_zdd *
drm_pagemap_zdd_alloc(struct drm_pagemap *dpagemap)
{
        struct drm_pagemap_zdd *zdd;

        zdd = kmalloc_obj(*zdd);
        if (!zdd)
                return NULL;

        kref_init(&zdd->refcount);
        zdd->devmem_allocation = NULL;
        zdd->dpagemap = drm_pagemap_get(dpagemap);

        return zdd;
}

/**
 * drm_pagemap_zdd_get() - Get a reference to a zdd structure.
 * @zdd: Pointer to the zdd structure.
 *
 * This function increments the reference count of the provided zdd structure.
 *
 * Return: Pointer to the zdd structure.
 */
static struct drm_pagemap_zdd *drm_pagemap_zdd_get(struct drm_pagemap_zdd *zdd)
{
        kref_get(&zdd->refcount);
        return zdd;
}

/**
 * drm_pagemap_zdd_destroy() - Destroy a zdd structure.
 * @ref: Pointer to the reference count structure.
 *
 * This function queues the destroy_work of the zdd for asynchronous destruction.
 */
static void drm_pagemap_zdd_destroy(struct kref *ref)
{
        struct drm_pagemap_zdd *zdd =
                container_of(ref, struct drm_pagemap_zdd, refcount);
        struct drm_pagemap_devmem *devmem = zdd->devmem_allocation;
        struct drm_pagemap *dpagemap = zdd->dpagemap;

        if (devmem) {
                complete_all(&devmem->detached);
                if (devmem->ops->devmem_release)
                        devmem->ops->devmem_release(devmem);
        }
        kfree(zdd);
        drm_pagemap_put(dpagemap);
}

/**
 * drm_pagemap_zdd_put() - Put a zdd reference.
 * @zdd: Pointer to the zdd structure.
 *
 * This function decrements the reference count of the provided zdd structure
 * and schedules its destruction if the count drops to zero.
 */
static void drm_pagemap_zdd_put(struct drm_pagemap_zdd *zdd)
{
        kref_put(&zdd->refcount, drm_pagemap_zdd_destroy);
}

/**
 * drm_pagemap_migration_unlock_put_folio() - Put a migration folio
 * @folio: Pointer to the folio to put
 *
 * This function unlocks and puts a folio.
 */
static void drm_pagemap_migration_unlock_put_folio(struct folio *folio)
{
        folio_unlock(folio);
        folio_put(folio);
}

/**
 * drm_pagemap_migration_unlock_put_pages() - Put migration pages
 * @npages: Number of pages
 * @migrate_pfn: Array of migrate page frame numbers
 *
 * This function unlocks and puts an array of pages.
 */
static void drm_pagemap_migration_unlock_put_pages(unsigned long npages,
                                                   unsigned long *migrate_pfn)
{
        unsigned long i;

        for (i = 0; i < npages;) {
                struct page *page;
                struct folio *folio;
                unsigned int order = 0;

                if (!migrate_pfn[i])
                        goto next;

                page = migrate_pfn_to_page(migrate_pfn[i]);
                folio = page_folio(page);
                order = folio_order(folio);

                drm_pagemap_migration_unlock_put_folio(folio);
                migrate_pfn[i] = 0;

next:
                i += NR_PAGES(order);
        }
}

/**
 * drm_pagemap_get_devmem_page() - Get a reference to a device memory page
 * @page: Pointer to the page
 * @order: Order
 * @zdd: Pointer to the GPU SVM zone device data
 *
 * This function associates the given page with the specified GPU SVM zone
 * device data and initializes it for zone device usage.
 */
static void drm_pagemap_get_devmem_page(struct page *page,
                                        unsigned int order,
                                        struct drm_pagemap_zdd *zdd)
{
        zone_device_folio_init((struct folio *)page, zdd->dpagemap->pagemap,
                               order);
        folio_set_zone_device_data(page_folio(page), drm_pagemap_zdd_get(zdd));
}

/**
 * drm_pagemap_migrate_map_device_private_pages() - Map device private migration
 * pages for GPU SVM migration
 * @dev: The device performing the migration.
 * @local_dpagemap: The drm_pagemap local to the migrating device.
 * @pagemap_addr: Array to store DMA information corresponding to mapped pages.
 * @migrate_pfn: Array of page frame numbers of system pages or peer pages to map.
 * @npages: Number of system pages or peer pages to map.
 * @dir: Direction of data transfer (e.g., DMA_BIDIRECTIONAL)
 * @mdetails: Details governing the migration behaviour.
 *
 * This function maps pages of memory for migration usage in GPU SVM. It
 * iterates over each page frame number provided in @migrate_pfn, maps the
 * corresponding page, and stores the DMA address in the provided @dma_addr
 * array.
 *
 * Returns: 0 on success, -EFAULT if an error occurs during mapping.
 */
static int
drm_pagemap_migrate_map_device_private_pages(struct device *dev,
                                             struct drm_pagemap *local_dpagemap,
                                             struct drm_pagemap_addr *pagemap_addr,
                                             unsigned long *migrate_pfn,
                                             unsigned long npages,
                                             enum dma_data_direction dir,
                                             const struct drm_pagemap_migrate_details *mdetails)
{
        unsigned long num_peer_pages = 0, num_local_pages = 0, i;

        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(migrate_pfn[i]);
                struct drm_pagemap_zdd *zdd;
                struct drm_pagemap *dpagemap;
                struct drm_pagemap_addr addr;
                struct folio *folio;
                unsigned int order = 0;

                if (!page)
                        goto next;

                WARN_ON_ONCE(!is_device_private_page(page));
                folio = page_folio(page);
                order = folio_order(folio);

                zdd = drm_pagemap_page_zone_device_data(page);
                dpagemap = zdd->dpagemap;

                if (dpagemap == local_dpagemap) {
                        if (!mdetails->can_migrate_same_pagemap)
                                goto next;

                        num_local_pages += NR_PAGES(order);
                } else {
                        num_peer_pages += NR_PAGES(order);
                }

                addr = dpagemap->ops->device_map(dpagemap, dev, page, order, dir);
                if (dma_mapping_error(dev, addr.addr))
                        return -EFAULT;

                pagemap_addr[i] = addr;

next:
                i += NR_PAGES(order);
        }

        if (num_peer_pages)
                drm_dbg(local_dpagemap->drm, "Migrating %lu peer pages over interconnect.\n",
                        num_peer_pages);
        if (num_local_pages)
                drm_dbg(local_dpagemap->drm, "Migrating %lu local pages over interconnect.\n",
                        num_local_pages);

        return 0;
}

/**
 * struct drm_pagemap_iova_state - DRM pagemap IOVA state
 * @dma_state: DMA IOVA state.
 * @offset: Current offset in IOVA.
 *
 * This structure acts as an iterator for packing all IOVA addresses within a
 * contiguous range.
 */
struct drm_pagemap_iova_state {
        struct dma_iova_state dma_state;
        unsigned long offset;
};

/**
 * drm_pagemap_migrate_map_system_pages() - Map system or device coherent
 * migration pages for GPU SVM migration
 * @dev: The device performing the migration.
 * @pagemap_addr: Array to store DMA information corresponding to mapped pages.
 * @migrate_pfn: Array of page frame numbers of system pages or peer pages to map.
 * @npages: Number of system or device coherent pages to map.
 * @dir: Direction of data transfer (e.g., DMA_BIDIRECTIONAL)
 * @state: DMA IOVA state for mapping.
 *
 * This function maps pages of memory for migration usage in GPU SVM. It
 * iterates over each page frame number provided in @migrate_pfn, maps the
 * corresponding page, and stores the DMA address in the provided @dma_addr
 * array.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int
drm_pagemap_migrate_map_system_pages(struct device *dev,
                                     struct drm_pagemap_addr *pagemap_addr,
                                     unsigned long *migrate_pfn,
                                     unsigned long npages,
                                     enum dma_data_direction dir,
                                     struct drm_pagemap_iova_state *state)
{
        unsigned long i;
        bool try_alloc = false;

        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(migrate_pfn[i]);
                dma_addr_t dma_addr;
                struct folio *folio;
                unsigned int order = 0;

                if (!page)
                        goto next;

                WARN_ON_ONCE(is_device_private_page(page));
                folio = page_folio(page);
                order = folio_order(folio);

                if (!try_alloc) {
                        dma_iova_try_alloc(dev, &state->dma_state,
                                           0, npages * PAGE_SIZE);
                        try_alloc = true;
                }

                if (dma_use_iova(&state->dma_state)) {
                        int err = dma_iova_link(dev, &state->dma_state,
                                                page_to_phys(page),
                                                state->offset, page_size(page),
                                                dir, 0);
                        if (err)
                                return err;

                        dma_addr = state->dma_state.addr + state->offset;
                        state->offset += page_size(page);
                } else {
                        dma_addr = dma_map_page(dev, page, 0, page_size(page),
                                                dir);
                        if (dma_mapping_error(dev, dma_addr))
                                return -EFAULT;
                }

                pagemap_addr[i] =
                        drm_pagemap_addr_encode(dma_addr,
                                                DRM_INTERCONNECT_SYSTEM,
                                                order, dir);

next:
                i += NR_PAGES(order);
        }

        if (dma_use_iova(&state->dma_state))
                return dma_iova_sync(dev, &state->dma_state, 0, state->offset);

        return 0;
}

/**
 * drm_pagemap_migrate_unmap_pages() - Unmap pages previously mapped for GPU SVM migration
 * @dev: The device for which the pages were mapped
 * @migrate_pfn: Array of migrate pfns set up for the mapped pages. Used to
 * determine the drm_pagemap of a peer device private page.
 * @pagemap_addr: Array of DMA information corresponding to mapped pages
 * @npages: Number of pages to unmap
 * @dir: Direction of data transfer (e.g., DMA_BIDIRECTIONAL)
 * @state: DMA IOVA state for mapping.
 *
 * This function unmaps previously mapped pages of memory for GPU Shared Virtual
 * Memory (SVM). It iterates over each DMA address provided in @pagemap_addr,
 * checks if it's valid and not already unmapped, and unmaps the corresponding
 * page.
 */
static void drm_pagemap_migrate_unmap_pages(struct device *dev,
                                            struct drm_pagemap_addr *pagemap_addr,
                                            unsigned long *migrate_pfn,
                                            unsigned long npages,
                                            enum dma_data_direction dir,
                                            struct drm_pagemap_iova_state *state)
{
        unsigned long i;

        if (state && dma_use_iova(&state->dma_state)) {
                dma_iova_destroy(dev, &state->dma_state, state->offset, dir, 0);
                return;
        }

        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(migrate_pfn[i]);

                if (!page || !pagemap_addr[i].addr || dma_mapping_error(dev, pagemap_addr[i].addr))
                        goto next;

                if (is_zone_device_page(page)) {
                        struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(page);
                        struct drm_pagemap *dpagemap = zdd->dpagemap;

                        dpagemap->ops->device_unmap(dpagemap, dev, &pagemap_addr[i]);
                } else {
                        dma_unmap_page(dev, pagemap_addr[i].addr,
                                       PAGE_SIZE << pagemap_addr[i].order, dir);
                }

next:
                i += NR_PAGES(pagemap_addr[i].order);
        }
}

static unsigned long
npages_in_range(unsigned long start, unsigned long end)
{
        return (end - start) >> PAGE_SHIFT;
}

static int
drm_pagemap_migrate_remote_to_local(struct drm_pagemap_devmem *devmem,
                                    struct device *remote_device,
                                    struct drm_pagemap *remote_dpagemap,
                                    unsigned long local_pfns[],
                                    struct page *remote_pages[],
                                    struct drm_pagemap_addr pagemap_addr[],
                                    unsigned long npages,
                                    const struct drm_pagemap_devmem_ops *ops,
                                    const struct drm_pagemap_migrate_details *mdetails)

{
        int err = drm_pagemap_migrate_map_device_private_pages(remote_device,
                                                               remote_dpagemap,
                                                               pagemap_addr,
                                                               local_pfns,
                                                               npages,
                                                               DMA_FROM_DEVICE,
                                                               mdetails);

        if (err)
                goto out;

        err = ops->copy_to_ram(remote_pages, pagemap_addr, npages,
                               devmem->pre_migrate_fence);
out:
        drm_pagemap_migrate_unmap_pages(remote_device, pagemap_addr, local_pfns,
                                        npages, DMA_FROM_DEVICE, NULL);
        return err;
}

static int
drm_pagemap_migrate_sys_to_dev(struct drm_pagemap_devmem *devmem,
                               unsigned long sys_pfns[],
                               struct page *local_pages[],
                               struct drm_pagemap_addr pagemap_addr[],
                               unsigned long npages,
                               const struct drm_pagemap_devmem_ops *ops,
                               struct drm_pagemap_iova_state *state)
{
        int err = drm_pagemap_migrate_map_system_pages(devmem->dev,
                                                       pagemap_addr, sys_pfns,
                                                       npages, DMA_TO_DEVICE,
                                                       state);

        if (err)
                goto out;

        err = ops->copy_to_devmem(local_pages, pagemap_addr, npages,
                                  devmem->pre_migrate_fence);
out:
        drm_pagemap_migrate_unmap_pages(devmem->dev, pagemap_addr, sys_pfns, npages,
                                        DMA_TO_DEVICE, state);
        return err;
}

/**
 * struct migrate_range_loc - Cursor into the loop over migrate_pfns for migrating to
 * device.
 * @start: The current loop index.
 * @device: migrating device.
 * @dpagemap: Pointer to struct drm_pagemap used by the migrating device.
 * @ops: The copy ops to be used for the migrating device.
 */
struct migrate_range_loc {
        unsigned long start;
        struct device *device;
        struct drm_pagemap *dpagemap;
        const struct drm_pagemap_devmem_ops *ops;
};

static int drm_pagemap_migrate_range(struct drm_pagemap_devmem *devmem,
                                     unsigned long src_pfns[],
                                     unsigned long dst_pfns[],
                                     struct page *pages[],
                                     struct drm_pagemap_addr pagemap_addr[],
                                     struct migrate_range_loc *last,
                                     const struct migrate_range_loc *cur,
                                     const struct drm_pagemap_migrate_details *mdetails)
{
        struct drm_pagemap_iova_state state = {};
        int ret = 0;

        if (cur->start == 0)
                goto out;

        if (cur->start <= last->start)
                return 0;

        if (cur->dpagemap == last->dpagemap && cur->ops == last->ops)
                return 0;

        if (last->dpagemap)
                ret = drm_pagemap_migrate_remote_to_local(devmem,
                                                          last->device,
                                                          last->dpagemap,
                                                          &dst_pfns[last->start],
                                                          &pages[last->start],
                                                          &pagemap_addr[last->start],
                                                          cur->start - last->start,
                                                          last->ops, mdetails);

        else
                ret = drm_pagemap_migrate_sys_to_dev(devmem,
                                                     &src_pfns[last->start],
                                                     &pages[last->start],
                                                     &pagemap_addr[last->start],
                                                     cur->start - last->start,
                                                     last->ops, &state);

out:
        *last = *cur;
        return ret;
}

/**
 * drm_pagemap_cpages() - Count collected pages
 * @migrate_pfn: Array of migrate_pfn entries to account
 * @npages: Number of entries in @migrate_pfn
 *
 * Compute the total number of minimum-sized pages represented by the
 * collected entries in @migrate_pfn. The total is derived from the
 * order encoded in each entry.
 *
 * Return: Total number of minimum-sized pages.
 */
static int drm_pagemap_cpages(unsigned long *migrate_pfn, unsigned long npages)
{
        unsigned long i, cpages = 0;

        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(migrate_pfn[i]);
                struct folio *folio;
                unsigned int order = 0;

                if (page) {
                        folio = page_folio(page);
                        order = folio_order(folio);
                        cpages += NR_PAGES(order);
                } else if (migrate_pfn[i] & MIGRATE_PFN_COMPOUND) {
                        order = HPAGE_PMD_ORDER;
                        cpages += NR_PAGES(order);
                }

                i += NR_PAGES(order);
        }

        return cpages;
}

/**
 * drm_pagemap_migrate_to_devmem() - Migrate a struct mm_struct range to device memory
 * @devmem_allocation: The device memory allocation to migrate to.
 * The caller should hold a reference to the device memory allocation,
 * and the reference is consumed by this function even if it returns with
 * an error.
 * @mm: Pointer to the struct mm_struct.
 * @start: Start of the virtual address range to migrate.
 * @end: End of the virtual address range to migrate.
 * @mdetails: Details to govern the migration.
 *
 * This function migrates the specified virtual address range to device memory.
 * It performs the necessary setup and invokes the driver-specific operations for
 * migration to device memory. Expected to be called while holding the mmap lock in
 * at least read mode.
 *
 * Note: The @timeslice_ms parameter can typically be used to force data to
 * remain in pagemap pages long enough for a GPU to perform a task and to prevent
 * a migration livelock. One alternative would be for the GPU driver to block
 * in a mmu_notifier for the specified amount of time, but adding the
 * functionality to the pagemap is likely nicer to the system as a whole.
 *
 * Return: %0 on success, negative error code on failure.
 */
int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
                                  struct mm_struct *mm,
                                  unsigned long start, unsigned long end,
                                  const struct drm_pagemap_migrate_details *mdetails)
{
        const struct drm_pagemap_devmem_ops *ops = devmem_allocation->ops;
        struct drm_pagemap *dpagemap = devmem_allocation->dpagemap;
        struct dev_pagemap *pagemap = dpagemap->pagemap;
        struct migrate_vma migrate = {
                .start          = start,
                .end            = end,
                .pgmap_owner    = pagemap->owner,
                .flags          = MIGRATE_VMA_SELECT_SYSTEM | MIGRATE_VMA_SELECT_DEVICE_COHERENT |
                MIGRATE_VMA_SELECT_DEVICE_PRIVATE | MIGRATE_VMA_SELECT_COMPOUND,
        };
        unsigned long i, npages = npages_in_range(start, end);
        unsigned long own_pages = 0, migrated_pages = 0;
        struct migrate_range_loc cur, last = {.device = dpagemap->drm->dev, .ops = ops};
        struct vm_area_struct *vas;
        struct drm_pagemap_zdd *zdd = NULL;
        struct page **pages;
        struct drm_pagemap_addr *pagemap_addr;
        void *buf;
        int err;

        mmap_assert_locked(mm);

        if (!ops->populate_devmem_pfn || !ops->copy_to_devmem ||
            !ops->copy_to_ram)
                return -EOPNOTSUPP;

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

        if (end > vas->vm_end || start < vas->vm_start) {
                err = -EINVAL;
                goto err_out;
        }

        if (!vma_is_anonymous(vas)) {
                err = -EBUSY;
                goto err_out;
        }

        buf = kvcalloc(npages, 2 * sizeof(*migrate.src) + sizeof(*pagemap_addr) +
                       sizeof(*pages), GFP_KERNEL);
        if (!buf) {
                err = -ENOMEM;
                goto err_out;
        }
        pagemap_addr = buf + (2 * sizeof(*migrate.src) * npages);
        pages = buf + (2 * sizeof(*migrate.src) + sizeof(*pagemap_addr)) * npages;

        zdd = drm_pagemap_zdd_alloc(dpagemap);
        if (!zdd) {
                err = -ENOMEM;
                kvfree(buf);
                goto err_out;
        }
        zdd->devmem_allocation = devmem_allocation;     /* Owns ref */

        migrate.vma = vas;
        migrate.src = buf;
        migrate.dst = migrate.src + npages;

        err = migrate_vma_setup(&migrate);
        if (err)
                goto err_free;

        if (!migrate.cpages) {
                /* No pages to migrate. Raced or unknown device pages. */
                err = -EBUSY;
                goto err_free;
        }

        if (migrate.cpages != npages &&
            drm_pagemap_cpages(migrate.src, npages) != npages) {
                /*
                 * Some pages to migrate. But we want to migrate all or
                 * nothing. Raced or unknown device pages.
                 */
                err = -EBUSY;
                goto err_aborted_migration;
        }

        /* Count device-private pages to migrate */
        for (i = 0; i < npages;) {
                struct page *src_page = migrate_pfn_to_page(migrate.src[i]);
                unsigned long nr_pages = src_page ? NR_PAGES(folio_order(page_folio(src_page))) : 1;

                if (src_page && is_zone_device_page(src_page)) {
                        if (page_pgmap(src_page) == pagemap)
                                own_pages += nr_pages;
                }

                i += nr_pages;
        }

        drm_dbg(dpagemap->drm, "Total pages %lu; Own pages: %lu.\n",
                npages, own_pages);
        if (own_pages == npages) {
                err = 0;
                drm_dbg(dpagemap->drm, "Migration wasn't necessary.\n");
                goto err_aborted_migration;
        } else if (own_pages && !mdetails->can_migrate_same_pagemap) {
                err = -EBUSY;
                drm_dbg(dpagemap->drm, "Migration aborted due to fragmentation.\n");
                goto err_aborted_migration;
        }

        err = ops->populate_devmem_pfn(devmem_allocation, npages, migrate.dst);
        if (err) {
                npages = 0;
                goto err_finalize;
        }

        own_pages = 0;

        for (i = 0; i < npages;) {
                unsigned long j;
                struct page *page = pfn_to_page(migrate.dst[i]);
                struct page *src_page = migrate_pfn_to_page(migrate.src[i]);
                unsigned int order = 0;

                cur.start = i;
                pages[i] = NULL;
                if (src_page && is_device_private_page(src_page)) {
                        struct drm_pagemap_zdd *src_zdd =
                                drm_pagemap_page_zone_device_data(src_page);

                        if (page_pgmap(src_page) == pagemap &&
                            !mdetails->can_migrate_same_pagemap) {
                                migrate.dst[i] = 0;
                                own_pages++;
                                goto next;
                        }
                        cur.dpagemap = src_zdd->dpagemap;
                        cur.ops = src_zdd->devmem_allocation->ops;
                        cur.device = cur.dpagemap->drm->dev;
                        pages[i] = src_page;
                }
                if (!pages[i]) {
                        cur.dpagemap = NULL;
                        cur.ops = ops;
                        cur.device = dpagemap->drm->dev;
                        pages[i] = page;
                }
                migrate.dst[i] = migrate_pfn(migrate.dst[i]);

                if (migrate.src[i] & MIGRATE_PFN_COMPOUND) {
                        drm_WARN_ONCE(dpagemap->drm, src_page &&
                                      folio_order(page_folio(src_page)) != HPAGE_PMD_ORDER,
                                      "Unexpected folio order\n");

                        order = HPAGE_PMD_ORDER;
                        migrate.dst[i] |= MIGRATE_PFN_COMPOUND;

                        for (j = 1; j < NR_PAGES(order) && i + j < npages; j++)
                                migrate.dst[i + j] = 0;
                }

                drm_pagemap_get_devmem_page(page, order, zdd);

                /* If we switched the migrating drm_pagemap, migrate previous pages now */
                err = drm_pagemap_migrate_range(devmem_allocation, migrate.src, migrate.dst,
                                                pages, pagemap_addr, &last, &cur,
                                                mdetails);
                if (err) {
                        npages = i + 1;
                        goto err_finalize;
                }

next:
                i += NR_PAGES(order);
        }

        cur.start = npages;
        cur.ops = NULL; /* Force migration */
        err = drm_pagemap_migrate_range(devmem_allocation, migrate.src, migrate.dst,
                                        pages, pagemap_addr, &last, &cur, mdetails);
        if (err)
                goto err_finalize;

        drm_WARN_ON(dpagemap->drm, !!own_pages);

        dma_fence_put(devmem_allocation->pre_migrate_fence);
        devmem_allocation->pre_migrate_fence = NULL;

        /* Upon success bind devmem allocation to range and zdd */
        devmem_allocation->timeslice_expiration = get_jiffies_64() +
                msecs_to_jiffies(mdetails->timeslice_ms);

err_finalize:
        if (err) {
                drm_pagemap_migration_unlock_put_pages(npages, migrate.dst);
                for (i = npages; i < npages_in_range(start, end); ++i)
                        migrate.dst[i] = 0;
        }
err_aborted_migration:
        migrate_vma_pages(&migrate);

        for (i = 0; !err && i < npages;) {
                struct page *page = migrate_pfn_to_page(migrate.src[i]);
                unsigned long nr_pages = page ? NR_PAGES(folio_order(page_folio(page))) : 1;

                if (migrate.src[i] & MIGRATE_PFN_MIGRATE)
                        migrated_pages += nr_pages;

                i += nr_pages;
        }

        if (!err && migrated_pages < npages - own_pages) {
                drm_dbg(dpagemap->drm, "Raced while finalizing migration.\n");
                err = -EBUSY;
        }

        migrate_vma_finalize(&migrate);
err_free:
        drm_pagemap_zdd_put(zdd);
        kvfree(buf);
        return err;

err_out:
        devmem_allocation->ops->devmem_release(devmem_allocation);
        return err;
}
EXPORT_SYMBOL_GPL(drm_pagemap_migrate_to_devmem);

/**
 * drm_pagemap_migrate_populate_ram_pfn() - Populate RAM PFNs for a VM area
 * @vas: Pointer to the VM area structure, can be NULL
 * @fault_page: Fault page
 * @npages: Number of pages to populate
 * @mpages: Number of pages to migrate
 * @src_mpfn: Source array of migrate PFNs
 * @mpfn: Array of migrate PFNs to populate
 * @addr: Start address for PFN allocation
 *
 * This function populates the RAM migrate page frame numbers (PFNs) for the
 * specified VM area structure. It allocates and locks pages in the VM area for
 * RAM usage. If vas is non-NULL use alloc_page_vma for allocation, if NULL use
 * alloc_page for allocation.
 *
 * Return: 0 on success, negative error code on failure.
 */
static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas,
                                                struct page *fault_page,
                                                unsigned long npages,
                                                unsigned long *mpages,
                                                unsigned long *src_mpfn,
                                                unsigned long *mpfn,
                                                unsigned long addr)
{
        unsigned long i;

        for (i = 0; i < npages;) {
                struct page *page = NULL, *src_page;
                struct folio *folio;
                unsigned int order = 0;

                if (!(src_mpfn[i] & MIGRATE_PFN_MIGRATE))
                        goto next;

                src_page = migrate_pfn_to_page(src_mpfn[i]);
                if (!src_page)
                        goto next;

                if (fault_page) {
                        if (drm_pagemap_page_zone_device_data(src_page) !=
                            drm_pagemap_page_zone_device_data(fault_page))
                                goto next;
                }

                order = folio_order(page_folio(src_page));

                /* TODO: Support fallback to single pages if THP allocation fails */
                if (vas)
                        folio = vma_alloc_folio(GFP_HIGHUSER, order, vas, addr);
                else
                        folio = folio_alloc(GFP_HIGHUSER, order);

                if (!folio)
                        goto free_pages;

                page = folio_page(folio, 0);
                mpfn[i] = migrate_pfn(page_to_pfn(page));

                if (order)
                        mpfn[i] |= MIGRATE_PFN_COMPOUND;
next:
                if (page)
                        addr += page_size(page);
                else
                        addr += PAGE_SIZE;

                i += NR_PAGES(order);
        }

        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(mpfn[i]);
                unsigned int order = 0;

                if (!page)
                        goto next_lock;

                WARN_ON_ONCE(!folio_trylock(page_folio(page)));

                order = folio_order(page_folio(page));
                *mpages += NR_PAGES(order);

next_lock:
                i += NR_PAGES(order);
        }

        return 0;

free_pages:
        for (i = 0; i < npages;) {
                struct page *page = migrate_pfn_to_page(mpfn[i]);
                unsigned int order = 0;

                if (!page)
                        goto next_put;

                put_page(page);
                mpfn[i] = 0;

                order = folio_order(page_folio(page));

next_put:
                i += NR_PAGES(order);
        }
        return -ENOMEM;
}

static void drm_pagemap_dev_unhold_work(struct work_struct *work);
static LLIST_HEAD(drm_pagemap_unhold_list);
static DECLARE_WORK(drm_pagemap_work, drm_pagemap_dev_unhold_work);

/**
 * struct drm_pagemap_dev_hold - Struct to aid in drm_device release.
 * @link: Link into drm_pagemap_unhold_list for deferred reference releases.
 * @drm: drm device to put.
 *
 * When a struct drm_pagemap is released, we also need to release the
 * reference it holds on the drm device. However, typically that needs
 * to be done separately from a system-wide workqueue.
 * Each time a struct drm_pagemap is initialized
 * (or re-initialized if cached) therefore allocate a separate
 * drm_pagemap_dev_hold item, from which we put the drm device and
 * associated module.
 */
struct drm_pagemap_dev_hold {
        struct llist_node link;
        struct drm_device *drm;
};

static void drm_pagemap_release(struct kref *ref)
{
        struct drm_pagemap *dpagemap = container_of(ref, typeof(*dpagemap), ref);
        struct drm_pagemap_dev_hold *dev_hold = dpagemap->dev_hold;

        /*
         * We know the pagemap provider is alive at this point, since
         * the struct drm_pagemap_dev_hold holds a reference to the
         * pagemap provider drm_device and its module.
         */
        dpagemap->dev_hold = NULL;
        drm_pagemap_shrinker_add(dpagemap);
        llist_add(&dev_hold->link, &drm_pagemap_unhold_list);
        schedule_work(&drm_pagemap_work);
        /*
         * Here, either the provider device is still alive, since if called from
         * page_free(), the caller is holding a reference on the dev_pagemap,
         * or if called from drm_pagemap_put(), the direct caller is still alive.
         * This ensures we can't race with THIS module unload.
         */
}

static void drm_pagemap_dev_unhold_work(struct work_struct *work)
{
        struct llist_node *node = llist_del_all(&drm_pagemap_unhold_list);
        struct drm_pagemap_dev_hold *dev_hold, *next;

        /*
         * Deferred release of drm_pagemap provider device and module.
         * THIS module is kept alive during the release by the
         * flush_work() in the drm_pagemap_exit() function.
         */
        llist_for_each_entry_safe(dev_hold, next, node, link) {
                struct drm_device *drm = dev_hold->drm;
                struct module *module = drm->driver->fops->owner;

                drm_dbg(drm, "Releasing reference on provider device and module.\n");
                drm_dev_put(drm);
                module_put(module);
                kfree(dev_hold);
        }
}

static struct drm_pagemap_dev_hold *
drm_pagemap_dev_hold(struct drm_pagemap *dpagemap)
{
        struct drm_pagemap_dev_hold *dev_hold;
        struct drm_device *drm = dpagemap->drm;

        dev_hold = kzalloc_obj(*dev_hold);
        if (!dev_hold)
                return ERR_PTR(-ENOMEM);

        init_llist_node(&dev_hold->link);
        dev_hold->drm = drm;
        (void)try_module_get(drm->driver->fops->owner);
        drm_dev_get(drm);

        return dev_hold;
}

/**
 * drm_pagemap_reinit() - Reinitialize a drm_pagemap
 * @dpagemap: The drm_pagemap to reinitialize
 *
 * Reinitialize a drm_pagemap, for which drm_pagemap_release
 * has already been called. This interface is intended for the
 * situation where the driver caches a destroyed drm_pagemap.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_pagemap_reinit(struct drm_pagemap *dpagemap)
{
        dpagemap->dev_hold = drm_pagemap_dev_hold(dpagemap);
        if (IS_ERR(dpagemap->dev_hold))
                return PTR_ERR(dpagemap->dev_hold);

        kref_init(&dpagemap->ref);
        return 0;
}
EXPORT_SYMBOL(drm_pagemap_reinit);

/**
 * drm_pagemap_init() - Initialize a pre-allocated drm_pagemap
 * @dpagemap: The drm_pagemap to initialize.
 * @pagemap: The associated dev_pagemap providing the device
 * private pages.
 * @drm: The drm device. The drm_pagemap holds a reference on the
 * drm_device and the module owning the drm_device until
 * drm_pagemap_release(). This facilitates drm_pagemap exporting.
 * @ops: The drm_pagemap ops.
 *
 * Initialize and take an initial reference on a drm_pagemap.
 * After successful return, use drm_pagemap_put() to destroy.
 *
 ** Return: 0 on success, negative error code on error.
 */
int drm_pagemap_init(struct drm_pagemap *dpagemap,
                     struct dev_pagemap *pagemap,
                     struct drm_device *drm,
                     const struct drm_pagemap_ops *ops)
{
        kref_init(&dpagemap->ref);
        dpagemap->ops = ops;
        dpagemap->pagemap = pagemap;
        dpagemap->drm = drm;
        dpagemap->cache = NULL;
        INIT_LIST_HEAD(&dpagemap->shrink_link);

        return drm_pagemap_reinit(dpagemap);
}
EXPORT_SYMBOL(drm_pagemap_init);

/**
 * drm_pagemap_put() - Put a struct drm_pagemap reference
 * @dpagemap: Pointer to a struct drm_pagemap object.
 *
 * Puts a struct drm_pagemap reference and frees the drm_pagemap object
 * if the refount reaches zero.
 */
void drm_pagemap_put(struct drm_pagemap *dpagemap)
{
        if (likely(dpagemap)) {
                drm_pagemap_shrinker_might_lock(dpagemap);
                kref_put(&dpagemap->ref, drm_pagemap_release);
        }
}
EXPORT_SYMBOL(drm_pagemap_put);

/**
 * drm_pagemap_evict_to_ram() - Evict GPU SVM range to RAM
 * @devmem_allocation: Pointer to the device memory allocation
 *
 * Similar to __drm_pagemap_migrate_to_ram but does not require mmap lock and
 * migration done via migrate_device_* functions.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem *devmem_allocation)
{
        const struct drm_pagemap_devmem_ops *ops = devmem_allocation->ops;
        struct drm_pagemap_iova_state state = {};
        unsigned long npages, mpages = 0;
        struct page **pages;
        unsigned long *src, *dst;
        struct drm_pagemap_addr *pagemap_addr;
        void *buf;
        int i, err = 0;
        unsigned int retry_count = 2;

        npages = devmem_allocation->size >> PAGE_SHIFT;

retry:
        if (!mmget_not_zero(devmem_allocation->mm))
                return -EFAULT;

        buf = kvcalloc(npages, 2 * sizeof(*src) + sizeof(*pagemap_addr) +
                       sizeof(*pages), GFP_KERNEL);
        if (!buf) {
                err = -ENOMEM;
                goto err_out;
        }
        src = buf;
        dst = buf + (sizeof(*src) * npages);
        pagemap_addr = buf + (2 * sizeof(*src) * npages);
        pages = buf + (2 * sizeof(*src) + sizeof(*pagemap_addr)) * npages;

        err = ops->populate_devmem_pfn(devmem_allocation, npages, src);
        if (err)
                goto err_free;

        err = migrate_device_pfns(src, npages);
        if (err)
                goto err_free;

        err = drm_pagemap_migrate_populate_ram_pfn(NULL, NULL, npages, &mpages,
                                                   src, dst, 0);
        if (err || !mpages)
                goto err_finalize;

        err = drm_pagemap_migrate_map_system_pages(devmem_allocation->dev,
                                                   pagemap_addr,
                                                   dst, npages,
                                                   DMA_FROM_DEVICE, &state);
        if (err)
                goto err_finalize;

        for (i = 0; i < npages;) {
                unsigned int order = 0;

                pages[i] = migrate_pfn_to_page(src[i]);
                if (pages[i])
                        order = folio_order(page_folio(pages[i]));

                i += NR_PAGES(order);
        }

        err = ops->copy_to_ram(pages, pagemap_addr, npages, NULL);
        if (err)
                goto err_finalize;

err_finalize:
        if (err)
                drm_pagemap_migration_unlock_put_pages(npages, dst);
        migrate_device_pages(src, dst, npages);
        migrate_device_finalize(src, dst, npages);
        drm_pagemap_migrate_unmap_pages(devmem_allocation->dev, pagemap_addr, dst, npages,
                                        DMA_FROM_DEVICE, &state);

err_free:
        kvfree(buf);
err_out:
        mmput_async(devmem_allocation->mm);

        if (completion_done(&devmem_allocation->detached))
                return 0;

        if (retry_count--) {
                cond_resched();
                state = (struct drm_pagemap_iova_state){};
                goto retry;
        }

        return err ?: -EBUSY;
}
EXPORT_SYMBOL_GPL(drm_pagemap_evict_to_ram);

/**
 * __drm_pagemap_migrate_to_ram() - Migrate GPU SVM range to RAM (internal)
 * @vas: Pointer to the VM area structure
 * @page: Pointer to the page for fault handling.
 * @fault_addr: Fault address
 * @size: Size of migration
 *
 * This internal function performs the migration of the specified GPU SVM range
 * to RAM. It sets up the migration, populates + dma maps RAM PFNs, and
 * invokes the driver-specific operations for migration to RAM.
 *
 * Return: 0 on success, negative error code on failure.
 */
static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
                                        struct page *page,
                                        unsigned long fault_addr,
                                        unsigned long size)
{
        struct migrate_vma migrate = {
                .vma            = vas,
                .pgmap_owner    = page_pgmap(page)->owner,
                .flags          = MIGRATE_VMA_SELECT_DEVICE_PRIVATE |
                                  MIGRATE_VMA_SELECT_DEVICE_COHERENT |
                                  MIGRATE_VMA_SELECT_COMPOUND,
                .fault_page     = page,
        };
        struct drm_pagemap_iova_state state = {};
        struct drm_pagemap_zdd *zdd;
        const struct drm_pagemap_devmem_ops *ops;
        struct device *dev = NULL;
        unsigned long npages, mpages = 0;
        struct page **pages;
        struct drm_pagemap_addr *pagemap_addr;
        unsigned long start, end;
        void *buf;
        int i, err = 0;

        zdd = drm_pagemap_page_zone_device_data(page);
        if (time_before64(get_jiffies_64(), zdd->devmem_allocation->timeslice_expiration))
                return 0;

        start = ALIGN_DOWN(fault_addr, size);
        end = ALIGN(fault_addr + 1, size);

        /* Corner where VMA area struct has been partially unmapped */
        if (start < vas->vm_start)
                start = vas->vm_start;
        if (end > vas->vm_end)
                end = vas->vm_end;

        migrate.start = start;
        migrate.end = end;
        npages = npages_in_range(start, end);

        buf = kvcalloc(npages, 2 * sizeof(*migrate.src) + sizeof(*pagemap_addr) +
                       sizeof(*pages), GFP_KERNEL);
        if (!buf) {
                err = -ENOMEM;
                goto err_out;
        }
        pagemap_addr = buf + (2 * sizeof(*migrate.src) * npages);
        pages = buf + (2 * sizeof(*migrate.src) + sizeof(*pagemap_addr)) * npages;

        migrate.vma = vas;
        migrate.src = buf;
        migrate.dst = migrate.src + npages;

        err = migrate_vma_setup(&migrate);
        if (err)
                goto err_free;

        /* Raced with another CPU fault, nothing to do */
        if (!migrate.cpages)
                goto err_free;

        ops = zdd->devmem_allocation->ops;
        dev = zdd->devmem_allocation->dev;

        err = drm_pagemap_migrate_populate_ram_pfn(vas, page, npages, &mpages,
                                                   migrate.src, migrate.dst,
                                                   start);
        if (err)
                goto err_finalize;

        err = drm_pagemap_migrate_map_system_pages(dev, pagemap_addr,
                                                   migrate.dst, npages,
                                                   DMA_FROM_DEVICE, &state);
        if (err)
                goto err_finalize;

        for (i = 0; i < npages;) {
                unsigned int order = 0;

                pages[i] = migrate_pfn_to_page(migrate.src[i]);
                if (pages[i])
                        order = folio_order(page_folio(pages[i]));

                i += NR_PAGES(order);
        }

        err = ops->copy_to_ram(pages, pagemap_addr, npages, NULL);
        if (err)
                goto err_finalize;

err_finalize:
        if (err)
                drm_pagemap_migration_unlock_put_pages(npages, migrate.dst);
        migrate_vma_pages(&migrate);
        migrate_vma_finalize(&migrate);
        if (dev)
                drm_pagemap_migrate_unmap_pages(dev, pagemap_addr, migrate.dst,
                                                npages, DMA_FROM_DEVICE,
                                                &state);
err_free:
        kvfree(buf);
err_out:

        return err;
}

/**
 * drm_pagemap_folio_free() - Put GPU SVM zone device data associated with a folio
 * @folio: Pointer to the folio
 *
 * This function is a callback used to put the GPU SVM zone device data
 * associated with a page when it is being released.
 */
static void drm_pagemap_folio_free(struct folio *folio)
{
        struct page *page = folio_page(folio, 0);

        drm_pagemap_zdd_put(drm_pagemap_page_zone_device_data(page));
}

/**
 * drm_pagemap_migrate_to_ram() - Migrate a virtual range to RAM (page fault handler)
 * @vmf: Pointer to the fault information structure
 *
 * This function is a page fault handler used to migrate a virtual range
 * to ram. The device memory allocation in which the device page is found is
 * migrated in its entirety.
 *
 * Returns:
 * VM_FAULT_SIGBUS on failure, 0 on success.
 */
static vm_fault_t drm_pagemap_migrate_to_ram(struct vm_fault *vmf)
{
        struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(vmf->page);
        int err;

        err = __drm_pagemap_migrate_to_ram(vmf->vma,
                                           vmf->page, vmf->address,
                                           zdd->devmem_allocation->size);

        return err ? VM_FAULT_SIGBUS : 0;
}

static void drm_pagemap_folio_split(struct folio *orig_folio, struct folio *new_folio)
{
        struct drm_pagemap_zdd *zdd;

        if (!new_folio)
                return;

        new_folio->pgmap = orig_folio->pgmap;
        zdd = folio_zone_device_data(orig_folio);
        folio_set_zone_device_data(new_folio, drm_pagemap_zdd_get(zdd));
}

static const struct dev_pagemap_ops drm_pagemap_pagemap_ops = {
        .folio_free = drm_pagemap_folio_free,
        .migrate_to_ram = drm_pagemap_migrate_to_ram,
        .folio_split = drm_pagemap_folio_split,
};

/**
 * drm_pagemap_pagemap_ops_get() - Retrieve GPU SVM device page map operations
 *
 * Returns:
 * Pointer to the GPU SVM device page map operations structure.
 */
const struct dev_pagemap_ops *drm_pagemap_pagemap_ops_get(void)
{
        return &drm_pagemap_pagemap_ops;
}
EXPORT_SYMBOL_GPL(drm_pagemap_pagemap_ops_get);

/**
 * drm_pagemap_devmem_init() - Initialize a drm_pagemap device memory allocation
 *
 * @devmem_allocation: The struct drm_pagemap_devmem to initialize.
 * @dev: Pointer to the device structure which device memory allocation belongs to
 * @mm: Pointer to the mm_struct for the address space
 * @ops: Pointer to the operations structure for GPU SVM device memory
 * @dpagemap: The struct drm_pagemap we're allocating from.
 * @size: Size of device memory allocation
 * @pre_migrate_fence: Fence to wait for or pipeline behind before migration starts.
 * (May be NULL).
 */
void drm_pagemap_devmem_init(struct drm_pagemap_devmem *devmem_allocation,
                             struct device *dev, struct mm_struct *mm,
                             const struct drm_pagemap_devmem_ops *ops,
                             struct drm_pagemap *dpagemap, size_t size,
                             struct dma_fence *pre_migrate_fence)
{
        init_completion(&devmem_allocation->detached);
        devmem_allocation->dev = dev;
        devmem_allocation->mm = mm;
        devmem_allocation->ops = ops;
        devmem_allocation->dpagemap = dpagemap;
        devmem_allocation->size = size;
        devmem_allocation->pre_migrate_fence = pre_migrate_fence;
}
EXPORT_SYMBOL_GPL(drm_pagemap_devmem_init);

/**
 * drm_pagemap_page_to_dpagemap() - Return a pointer the drm_pagemap of a page
 * @page: The struct page.
 *
 * Return: A pointer to the struct drm_pagemap of a device private page that
 * was populated from the struct drm_pagemap. If the page was *not* populated
 * from a struct drm_pagemap, the result is undefined and the function call
 * may result in dereferencing and invalid address.
 */
struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page)
{
        struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(page);

        return zdd->devmem_allocation->dpagemap;
}
EXPORT_SYMBOL_GPL(drm_pagemap_page_to_dpagemap);

/**
 * drm_pagemap_populate_mm() - Populate a virtual range with device memory pages
 * @dpagemap: Pointer to the drm_pagemap managing the device memory
 * @start: Start of the virtual range to populate.
 * @end: End of the virtual range to populate.
 * @mm: Pointer to the virtual address space.
 * @timeslice_ms: The time requested for the migrated pagemap pages to
 * be present in @mm before being allowed to be migrated back.
 *
 * Attempt to populate a virtual range with device memory pages,
 * clearing them or migrating data from the existing pages if necessary.
 * The function is best effort only, and implementations may vary
 * in how hard they try to satisfy the request.
 *
 * Return: %0 on success, negative error code on error. If the hardware
 * device was removed / unbound the function will return %-ENODEV.
 */
int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
                            unsigned long start, unsigned long end,
                            struct mm_struct *mm,
                            unsigned long timeslice_ms)
{
        int err;

        if (!mmget_not_zero(mm))
                return -EFAULT;
        mmap_read_lock(mm);
        err = dpagemap->ops->populate_mm(dpagemap, start, end, mm,
                                         timeslice_ms);
        mmap_read_unlock(mm);
        mmput(mm);

        return err;
}
EXPORT_SYMBOL(drm_pagemap_populate_mm);

void drm_pagemap_destroy(struct drm_pagemap *dpagemap, bool is_atomic_or_reclaim)
{
        if (dpagemap->ops->destroy)
                dpagemap->ops->destroy(dpagemap, is_atomic_or_reclaim);
        else
                kfree(dpagemap);
}

static void drm_pagemap_exit(void)
{
        flush_work(&drm_pagemap_work);
        if (WARN_ON(!llist_empty(&drm_pagemap_unhold_list)))
                disable_work_sync(&drm_pagemap_work);
}
module_exit(drm_pagemap_exit);