// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright 2013 Red Hat Inc.
 *
 * Authors: Jérôme Glisse <jglisse@redhat.com>
 */
/*
 * Refer to include/linux/hmm.h for information about heterogeneous memory
 * management or HMM for short.
 */
#include <linux/mm.h>
#include <linux/hmm.h>
#include <linux/init.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mmzone.h>
#include <linux/pagemap.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memremap.h>
#include <linux/jump_label.h>
#include <linux/dma-mapping.h>
#include <linux/mmu_notifier.h>
#include <linux/memory_hotplug.h>

#define PA_SECTION_SIZE (1UL << PA_SECTION_SHIFT)

#if IS_ENABLED(CONFIG_HMM_MIRROR)
static const struct mmu_notifier_ops hmm_mmu_notifier_ops;

static inline struct hmm *mm_get_hmm(struct mm_struct *mm)
{
        struct hmm *hmm = READ_ONCE(mm->hmm);

        if (hmm && kref_get_unless_zero(&hmm->kref))
                return hmm;

        return NULL;
}

/**
 * hmm_get_or_create - register HMM against an mm (HMM internal)
 *
 * @mm: mm struct to attach to
 * Returns: returns an HMM object, either by referencing the existing
 *          (per-process) object, or by creating a new one.
 *
 * This is not intended to be used directly by device drivers. If mm already
 * has an HMM struct then it get a reference on it and returns it. Otherwise
 * it allocates an HMM struct, initializes it, associate it with the mm and
 * returns it.
 */
static struct hmm *hmm_get_or_create(struct mm_struct *mm)
{
        struct hmm *hmm = mm_get_hmm(mm);
        bool cleanup = false;

        if (hmm)
                return hmm;

        hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
        if (!hmm)
                return NULL;
        init_waitqueue_head(&hmm->wq);
        INIT_LIST_HEAD(&hmm->mirrors);
        init_rwsem(&hmm->mirrors_sem);
        hmm->mmu_notifier.ops = NULL;
        INIT_LIST_HEAD(&hmm->ranges);
        mutex_init(&hmm->lock);
        kref_init(&hmm->kref);
        hmm->notifiers = 0;
        hmm->dead = false;
        hmm->mm = mm;

        spin_lock(&mm->page_table_lock);
        if (!mm->hmm)
                mm->hmm = hmm;
        else
                cleanup = true;
        spin_unlock(&mm->page_table_lock);

        if (cleanup)
                goto error;

        /*
         * We should only get here if hold the mmap_sem in write mode ie on
         * registration of first mirror through hmm_mirror_register()
         */
        hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
        if (__mmu_notifier_register(&hmm->mmu_notifier, mm))
                goto error_mm;

        return hmm;

error_mm:
        spin_lock(&mm->page_table_lock);
        if (mm->hmm == hmm)
                mm->hmm = NULL;
        spin_unlock(&mm->page_table_lock);
error:
        kfree(hmm);
        return NULL;
}

static void hmm_free(struct kref *kref)
{
        struct hmm *hmm = container_of(kref, struct hmm, kref);
        struct mm_struct *mm = hmm->mm;

        mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);

        spin_lock(&mm->page_table_lock);
        if (mm->hmm == hmm)
                mm->hmm = NULL;
        spin_unlock(&mm->page_table_lock);

        kfree(hmm);
}

static inline void hmm_put(struct hmm *hmm)
{
        kref_put(&hmm->kref, hmm_free);
}

void hmm_mm_destroy(struct mm_struct *mm)
{
        struct hmm *hmm;

        spin_lock(&mm->page_table_lock);
        hmm = mm_get_hmm(mm);
        mm->hmm = NULL;
        if (hmm) {
                hmm->mm = NULL;
                hmm->dead = true;
                spin_unlock(&mm->page_table_lock);
                hmm_put(hmm);
                return;
        }

        spin_unlock(&mm->page_table_lock);
}

static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
        struct hmm *hmm = mm_get_hmm(mm);
        struct hmm_mirror *mirror;
        struct hmm_range *range;

        /* Report this HMM as dying. */
        hmm->dead = true;

        /* Wake-up everyone waiting on any range. */
        mutex_lock(&hmm->lock);
        list_for_each_entry(range, &hmm->ranges, list) {
                range->valid = false;
        }
        wake_up_all(&hmm->wq);
        mutex_unlock(&hmm->lock);

        down_write(&hmm->mirrors_sem);
        mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
                                          list);
        while (mirror) {
                list_del_init(&mirror->list);
                if (mirror->ops->release) {
                        /*
                         * Drop mirrors_sem so callback can wait on any pending
                         * work that might itself trigger mmu_notifier callback
                         * and thus would deadlock with us.
                         */
                        up_write(&hmm->mirrors_sem);
                        mirror->ops->release(mirror);
                        down_write(&hmm->mirrors_sem);
                }
                mirror = list_first_entry_or_null(&hmm->mirrors,
                                                  struct hmm_mirror, list);
        }
        up_write(&hmm->mirrors_sem);

        hmm_put(hmm);
}

static int hmm_invalidate_range_start(struct mmu_notifier *mn,
                        const struct mmu_notifier_range *nrange)
{
        struct hmm *hmm = mm_get_hmm(nrange->mm);
        struct hmm_mirror *mirror;
        struct hmm_update update;
        struct hmm_range *range;
        int ret = 0;

        VM_BUG_ON(!hmm);

        update.start = nrange->start;
        update.end = nrange->end;
        update.event = HMM_UPDATE_INVALIDATE;
        update.blockable = mmu_notifier_range_blockable(nrange);

        if (mmu_notifier_range_blockable(nrange))
                mutex_lock(&hmm->lock);
        else if (!mutex_trylock(&hmm->lock)) {
                ret = -EAGAIN;
                goto out;
        }
        hmm->notifiers++;
        list_for_each_entry(range, &hmm->ranges, list) {
                if (update.end < range->start || update.start >= range->end)
                        continue;

                range->valid = false;
        }
        mutex_unlock(&hmm->lock);

        if (mmu_notifier_range_blockable(nrange))
                down_read(&hmm->mirrors_sem);
        else if (!down_read_trylock(&hmm->mirrors_sem)) {
                ret = -EAGAIN;
                goto out;
        }
        list_for_each_entry(mirror, &hmm->mirrors, list) {
                int ret;

                ret = mirror->ops->sync_cpu_device_pagetables(mirror, &update);
                if (!update.blockable && ret == -EAGAIN) {
                        up_read(&hmm->mirrors_sem);
                        ret = -EAGAIN;
                        goto out;
                }
        }
        up_read(&hmm->mirrors_sem);

out:
        hmm_put(hmm);
        return ret;
}

static void hmm_invalidate_range_end(struct mmu_notifier *mn,
                        const struct mmu_notifier_range *nrange)
{
        struct hmm *hmm = mm_get_hmm(nrange->mm);

        VM_BUG_ON(!hmm);

        mutex_lock(&hmm->lock);
        hmm->notifiers--;
        if (!hmm->notifiers) {
                struct hmm_range *range;

                list_for_each_entry(range, &hmm->ranges, list) {
                        if (range->valid)
                                continue;
                        range->valid = true;
                }
                wake_up_all(&hmm->wq);
        }
        mutex_unlock(&hmm->lock);

        hmm_put(hmm);
}

static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
        .release                = hmm_release,
        .invalidate_range_start = hmm_invalidate_range_start,
        .invalidate_range_end   = hmm_invalidate_range_end,
};

/*
 * hmm_mirror_register() - register a mirror against an mm
 *
 * @mirror: new mirror struct to register
 * @mm: mm to register against
 *
 * To start mirroring a process address space, the device driver must register
 * an HMM mirror struct.
 *
 * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
 */
int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
{
        /* Sanity check */
        if (!mm || !mirror || !mirror->ops)
                return -EINVAL;

        mirror->hmm = hmm_get_or_create(mm);
        if (!mirror->hmm)
                return -ENOMEM;

        down_write(&mirror->hmm->mirrors_sem);
        list_add(&mirror->list, &mirror->hmm->mirrors);
        up_write(&mirror->hmm->mirrors_sem);

        return 0;
}
EXPORT_SYMBOL(hmm_mirror_register);

/*
 * hmm_mirror_unregister() - unregister a mirror
 *
 * @mirror: new mirror struct to register
 *
 * Stop mirroring a process address space, and cleanup.
 */
void hmm_mirror_unregister(struct hmm_mirror *mirror)
{
        struct hmm *hmm = READ_ONCE(mirror->hmm);

        if (hmm == NULL)
                return;

        down_write(&hmm->mirrors_sem);
        list_del_init(&mirror->list);
        /* To protect us against double unregister ... */
        mirror->hmm = NULL;
        up_write(&hmm->mirrors_sem);

        hmm_put(hmm);
}
EXPORT_SYMBOL(hmm_mirror_unregister);

struct hmm_vma_walk {
        struct hmm_range        *range;
        struct dev_pagemap      *pgmap;
        unsigned long           last;
        bool                    fault;
        bool                    block;
};

static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
                            bool write_fault, uint64_t *pfn)
{
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;
        vm_fault_t ret;

        flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;
        flags |= write_fault ? FAULT_FLAG_WRITE : 0;
        ret = handle_mm_fault(vma, addr, flags);
        if (ret & VM_FAULT_RETRY)
                return -EAGAIN;
        if (ret & VM_FAULT_ERROR) {
                *pfn = range->values[HMM_PFN_ERROR];
                return -EFAULT;
        }

        return -EBUSY;
}

static int hmm_pfns_bad(unsigned long addr,
                        unsigned long end,
                        struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        uint64_t *pfns = range->pfns;
        unsigned long i;

        i = (addr - range->start) >> PAGE_SHIFT;
        for (; addr < end; addr += PAGE_SIZE, i++)
                pfns[i] = range->values[HMM_PFN_ERROR];

        return 0;
}

/*
 * hmm_vma_walk_hole() - handle a range lacking valid pmd or pte(s)
 * @start: range virtual start address (inclusive)
 * @end: range virtual end address (exclusive)
 * @fault: should we fault or not ?
 * @write_fault: write fault ?
 * @walk: mm_walk structure
 * Returns: 0 on success, -EBUSY after page fault, or page fault error
 *
 * This function will be called whenever pmd_none() or pte_none() returns true,
 * or whenever there is no page directory covering the virtual address range.
 */
static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
                              bool fault, bool write_fault,
                              struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        uint64_t *pfns = range->pfns;
        unsigned long i, page_size;

        hmm_vma_walk->last = addr;
        page_size = hmm_range_page_size(range);
        i = (addr - range->start) >> range->page_shift;

        for (; addr < end; addr += page_size, i++) {
                pfns[i] = range->values[HMM_PFN_NONE];
                if (fault || write_fault) {
                        int ret;

                        ret = hmm_vma_do_fault(walk, addr, write_fault,
                                               &pfns[i]);
                        if (ret != -EBUSY)
                                return ret;
                }
        }

        return (fault || write_fault) ? -EBUSY : 0;
}

static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
                                      uint64_t pfns, uint64_t cpu_flags,
                                      bool *fault, bool *write_fault)
{
        struct hmm_range *range = hmm_vma_walk->range;

        if (!hmm_vma_walk->fault)
                return;

        /*
         * So we not only consider the individual per page request we also
         * consider the default flags requested for the range. The API can
         * be use in 2 fashions. The first one where the HMM user coalesce
         * multiple page fault into one request and set flags per pfns for
         * of those faults. The second one where the HMM user want to pre-
         * fault a range with specific flags. For the latter one it is a
         * waste to have the user pre-fill the pfn arrays with a default
         * flags value.
         */
        pfns = (pfns & range->pfn_flags_mask) | range->default_flags;

        /* We aren't ask to do anything ... */
        if (!(pfns & range->flags[HMM_PFN_VALID]))
                return;
        /* If this is device memory than only fault if explicitly requested */
        if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
                /* Do we fault on device memory ? */
                if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
                        *write_fault = pfns & range->flags[HMM_PFN_WRITE];
                        *fault = true;
                }
                return;
        }

        /* If CPU page table is not valid then we need to fault */
        *fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
        /* Need to write fault ? */
        if ((pfns & range->flags[HMM_PFN_WRITE]) &&
            !(cpu_flags & range->flags[HMM_PFN_WRITE])) {
                *write_fault = true;
                *fault = true;
        }
}

static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
                                 const uint64_t *pfns, unsigned long npages,
                                 uint64_t cpu_flags, bool *fault,
                                 bool *write_fault)
{
        unsigned long i;

        if (!hmm_vma_walk->fault) {
                *fault = *write_fault = false;
                return;
        }

        *fault = *write_fault = false;
        for (i = 0; i < npages; ++i) {
                hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags,
                                   fault, write_fault);
                if ((*write_fault))
                        return;
        }
}

static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
                             struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        bool fault, write_fault;
        unsigned long i, npages;
        uint64_t *pfns;

        i = (addr - range->start) >> PAGE_SHIFT;
        npages = (end - addr) >> PAGE_SHIFT;
        pfns = &range->pfns[i];
        hmm_range_need_fault(hmm_vma_walk, pfns, npages,
                             0, &fault, &write_fault);
        return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
}

static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
{
        if (pmd_protnone(pmd))
                return 0;
        return pmd_write(pmd) ? range->flags[HMM_PFN_VALID] |
                                range->flags[HMM_PFN_WRITE] :
                                range->flags[HMM_PFN_VALID];
}

static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
{
        if (!pud_present(pud))
                return 0;
        return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
                                range->flags[HMM_PFN_WRITE] :
                                range->flags[HMM_PFN_VALID];
}

static int hmm_vma_handle_pmd(struct mm_walk *walk,
                              unsigned long addr,
                              unsigned long end,
                              uint64_t *pfns,
                              pmd_t pmd)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned long pfn, npages, i;
        bool fault, write_fault;
        uint64_t cpu_flags;

        npages = (end - addr) >> PAGE_SHIFT;
        cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
        hmm_range_need_fault(hmm_vma_walk, pfns, npages, cpu_flags,
                             &fault, &write_fault);

        if (pmd_protnone(pmd) || fault || write_fault)
                return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);

        pfn = pmd_pfn(pmd) + pte_index(addr);
        for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
                if (pmd_devmap(pmd)) {
                        hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
                                              hmm_vma_walk->pgmap);
                        if (unlikely(!hmm_vma_walk->pgmap))
                                return -EBUSY;
                }
                pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags;
        }
        if (hmm_vma_walk->pgmap) {
                put_dev_pagemap(hmm_vma_walk->pgmap);
                hmm_vma_walk->pgmap = NULL;
        }
        hmm_vma_walk->last = end;
        return 0;
#else
        /* If THP is not enabled then we should never reach that code ! */
        return -EINVAL;
#endif
}

static inline uint64_t pte_to_hmm_pfn_flags(struct hmm_range *range, pte_t pte)
{
        if (pte_none(pte) || !pte_present(pte))
                return 0;
        return pte_write(pte) ? range->flags[HMM_PFN_VALID] |
                                range->flags[HMM_PFN_WRITE] :
                                range->flags[HMM_PFN_VALID];
}

static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
                              unsigned long end, pmd_t *pmdp, pte_t *ptep,
                              uint64_t *pfn)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;
        bool fault, write_fault;
        uint64_t cpu_flags;
        pte_t pte = *ptep;
        uint64_t orig_pfn = *pfn;

        *pfn = range->values[HMM_PFN_NONE];
        fault = write_fault = false;

        if (pte_none(pte)) {
                hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0,
                                   &fault, &write_fault);
                if (fault || write_fault)
                        goto fault;
                return 0;
        }

        if (!pte_present(pte)) {
                swp_entry_t entry = pte_to_swp_entry(pte);

                if (!non_swap_entry(entry)) {
                        if (fault || write_fault)
                                goto fault;
                        return 0;
                }

                /*
                 * This is a special swap entry, ignore migration, use
                 * device and report anything else as error.
                 */
                if (is_device_private_entry(entry)) {
                        cpu_flags = range->flags[HMM_PFN_VALID] |
                                range->flags[HMM_PFN_DEVICE_PRIVATE];
                        cpu_flags |= is_write_device_private_entry(entry) ?
                                range->flags[HMM_PFN_WRITE] : 0;
                        hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
                                           &fault, &write_fault);
                        if (fault || write_fault)
                                goto fault;
                        *pfn = hmm_device_entry_from_pfn(range,
                                            swp_offset(entry));
                        *pfn |= cpu_flags;
                        return 0;
                }

                if (is_migration_entry(entry)) {
                        if (fault || write_fault) {
                                pte_unmap(ptep);
                                hmm_vma_walk->last = addr;
                                migration_entry_wait(vma->vm_mm,
                                                     pmdp, addr);
                                return -EBUSY;
                        }
                        return 0;
                }

                /* Report error for everything else */
                *pfn = range->values[HMM_PFN_ERROR];
                return -EFAULT;
        } else {
                cpu_flags = pte_to_hmm_pfn_flags(range, pte);
                hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
                                   &fault, &write_fault);
        }

        if (fault || write_fault)
                goto fault;

        if (pte_devmap(pte)) {
                hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte),
                                              hmm_vma_walk->pgmap);
                if (unlikely(!hmm_vma_walk->pgmap))
                        return -EBUSY;
        } else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) {
                *pfn = range->values[HMM_PFN_SPECIAL];
                return -EFAULT;
        }

        *pfn = hmm_device_entry_from_pfn(range, pte_pfn(pte)) | cpu_flags;
        return 0;

fault:
        if (hmm_vma_walk->pgmap) {
                put_dev_pagemap(hmm_vma_walk->pgmap);
                hmm_vma_walk->pgmap = NULL;
        }
        pte_unmap(ptep);
        /* Fault any virtual address we were asked to fault */
        return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
}

static int hmm_vma_walk_pmd(pmd_t *pmdp,
                            unsigned long start,
                            unsigned long end,
                            struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;
        uint64_t *pfns = range->pfns;
        unsigned long addr = start, i;
        pte_t *ptep;
        pmd_t pmd;


again:
        pmd = READ_ONCE(*pmdp);
        if (pmd_none(pmd))
                return hmm_vma_walk_hole(start, end, walk);

        if (pmd_huge(pmd) && (range->vma->vm_flags & VM_HUGETLB))
                return hmm_pfns_bad(start, end, walk);

        if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
                bool fault, write_fault;
                unsigned long npages;
                uint64_t *pfns;

                i = (addr - range->start) >> PAGE_SHIFT;
                npages = (end - addr) >> PAGE_SHIFT;
                pfns = &range->pfns[i];

                hmm_range_need_fault(hmm_vma_walk, pfns, npages,
                                     0, &fault, &write_fault);
                if (fault || write_fault) {
                        hmm_vma_walk->last = addr;
                        pmd_migration_entry_wait(vma->vm_mm, pmdp);
                        return -EBUSY;
                }
                return 0;
        } else if (!pmd_present(pmd))
                return hmm_pfns_bad(start, end, walk);

        if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
                /*
                 * No need to take pmd_lock here, even if some other threads
                 * is splitting the huge pmd we will get that event through
                 * mmu_notifier callback.
                 *
                 * So just read pmd value and check again its a transparent
                 * huge or device mapping one and compute corresponding pfn
                 * values.
                 */
                pmd = pmd_read_atomic(pmdp);
                barrier();
                if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
                        goto again;

                i = (addr - range->start) >> PAGE_SHIFT;
                return hmm_vma_handle_pmd(walk, addr, end, &pfns[i], pmd);
        }

        /*
         * We have handled all the valid case above ie either none, migration,
         * huge or transparent huge. At this point either it is a valid pmd
         * entry pointing to pte directory or it is a bad pmd that will not
         * recover.
         */
        if (pmd_bad(pmd))
                return hmm_pfns_bad(start, end, walk);

        ptep = pte_offset_map(pmdp, addr);
        i = (addr - range->start) >> PAGE_SHIFT;
        for (; addr < end; addr += PAGE_SIZE, ptep++, i++) {
                int r;

                r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, &pfns[i]);
                if (r) {
                        /* hmm_vma_handle_pte() did unmap pte directory */
                        hmm_vma_walk->last = addr;
                        return r;
                }
        }
        if (hmm_vma_walk->pgmap) {
                /*
                 * We do put_dev_pagemap() here and not in hmm_vma_handle_pte()
                 * so that we can leverage get_dev_pagemap() optimization which
                 * will not re-take a reference on a pgmap if we already have
                 * one.
                 */
                put_dev_pagemap(hmm_vma_walk->pgmap);
                hmm_vma_walk->pgmap = NULL;
        }
        pte_unmap(ptep - 1);

        hmm_vma_walk->last = addr;
        return 0;
}

static int hmm_vma_walk_pud(pud_t *pudp,
                            unsigned long start,
                            unsigned long end,
                            struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned long addr = start, next;
        pmd_t *pmdp;
        pud_t pud;
        int ret;

again:
        pud = READ_ONCE(*pudp);
        if (pud_none(pud))
                return hmm_vma_walk_hole(start, end, walk);

        if (pud_huge(pud) && pud_devmap(pud)) {
                unsigned long i, npages, pfn;
                uint64_t *pfns, cpu_flags;
                bool fault, write_fault;

                if (!pud_present(pud))
                        return hmm_vma_walk_hole(start, end, walk);

                i = (addr - range->start) >> PAGE_SHIFT;
                npages = (end - addr) >> PAGE_SHIFT;
                pfns = &range->pfns[i];

                cpu_flags = pud_to_hmm_pfn_flags(range, pud);
                hmm_range_need_fault(hmm_vma_walk, pfns, npages,
                                     cpu_flags, &fault, &write_fault);
                if (fault || write_fault)
                        return hmm_vma_walk_hole_(addr, end, fault,
                                                write_fault, walk);

#ifdef CONFIG_HUGETLB_PAGE
                pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
                for (i = 0; i < npages; ++i, ++pfn) {
                        hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
                                              hmm_vma_walk->pgmap);
                        if (unlikely(!hmm_vma_walk->pgmap))
                                return -EBUSY;
                        pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
                                  cpu_flags;
                }
                if (hmm_vma_walk->pgmap) {
                        put_dev_pagemap(hmm_vma_walk->pgmap);
                        hmm_vma_walk->pgmap = NULL;
                }
                hmm_vma_walk->last = end;
                return 0;
#else
                return -EINVAL;
#endif
        }

        split_huge_pud(walk->vma, pudp, addr);
        if (pud_none(*pudp))
                goto again;

        pmdp = pmd_offset(pudp, addr);
        do {
                next = pmd_addr_end(addr, end);
                ret = hmm_vma_walk_pmd(pmdp, addr, next, walk);
                if (ret)
                        return ret;
        } while (pmdp++, addr = next, addr != end);

        return 0;
}

static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
                                      unsigned long start, unsigned long end,
                                      struct mm_walk *walk)
{
#ifdef CONFIG_HUGETLB_PAGE
        unsigned long addr = start, i, pfn, mask, size, pfn_inc;
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;
        struct hstate *h = hstate_vma(vma);
        uint64_t orig_pfn, cpu_flags;
        bool fault, write_fault;
        spinlock_t *ptl;
        pte_t entry;
        int ret = 0;

        size = 1UL << huge_page_shift(h);
        mask = size - 1;
        if (range->page_shift != PAGE_SHIFT) {
                /* Make sure we are looking at full page. */
                if (start & mask)
                        return -EINVAL;
                if (end < (start + size))
                        return -EINVAL;
                pfn_inc = size >> PAGE_SHIFT;
        } else {
                pfn_inc = 1;
                size = PAGE_SIZE;
        }


        ptl = huge_pte_lock(hstate_vma(walk->vma), walk->mm, pte);
        entry = huge_ptep_get(pte);

        i = (start - range->start) >> range->page_shift;
        orig_pfn = range->pfns[i];
        range->pfns[i] = range->values[HMM_PFN_NONE];
        cpu_flags = pte_to_hmm_pfn_flags(range, entry);
        fault = write_fault = false;
        hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
                           &fault, &write_fault);
        if (fault || write_fault) {
                ret = -ENOENT;
                goto unlock;
        }

        pfn = pte_pfn(entry) + ((start & mask) >> range->page_shift);
        for (; addr < end; addr += size, i++, pfn += pfn_inc)
                range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
                                 cpu_flags;
        hmm_vma_walk->last = end;

unlock:
        spin_unlock(ptl);

        if (ret == -ENOENT)
                return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);

        return ret;
#else /* CONFIG_HUGETLB_PAGE */
        return -EINVAL;
#endif
}

static void hmm_pfns_clear(struct hmm_range *range,
                           uint64_t *pfns,
                           unsigned long addr,
                           unsigned long end)
{
        for (; addr < end; addr += PAGE_SIZE, pfns++)
                *pfns = range->values[HMM_PFN_NONE];
}

/*
 * hmm_range_register() - start tracking change to CPU page table over a range
 * @range: range
 * @mm: the mm struct for the range of virtual address
 * @start: start virtual address (inclusive)
 * @end: end virtual address (exclusive)
 * @page_shift: expect page shift for the range
 * Returns 0 on success, -EFAULT if the address space is no longer valid
 *
 * Track updates to the CPU page table see include/linux/hmm.h
 */
int hmm_range_register(struct hmm_range *range,
                       struct mm_struct *mm,
                       unsigned long start,
                       unsigned long end,
                       unsigned page_shift)
{
        unsigned long mask = ((1UL << page_shift) - 1UL);

        range->valid = false;
        range->hmm = NULL;

        if ((start & mask) || (end & mask))
                return -EINVAL;
        if (start >= end)
                return -EINVAL;

        range->page_shift = page_shift;
        range->start = start;
        range->end = end;

        range->hmm = hmm_get_or_create(mm);
        if (!range->hmm)
                return -EFAULT;

        /* Check if hmm_mm_destroy() was call. */
        if (range->hmm->mm == NULL || range->hmm->dead) {
                hmm_put(range->hmm);
                return -EFAULT;
        }

        /* Initialize range to track CPU page table update */
        mutex_lock(&range->hmm->lock);

        list_add_rcu(&range->list, &range->hmm->ranges);

        /*
         * If there are any concurrent notifiers we have to wait for them for
         * the range to be valid (see hmm_range_wait_until_valid()).
         */
        if (!range->hmm->notifiers)
                range->valid = true;
        mutex_unlock(&range->hmm->lock);

        return 0;
}
EXPORT_SYMBOL(hmm_range_register);

/*
 * hmm_range_unregister() - stop tracking change to CPU page table over a range
 * @range: range
 *
 * Range struct is used to track updates to the CPU page table after a call to
 * hmm_range_register(). See include/linux/hmm.h for how to use it.
 */
void hmm_range_unregister(struct hmm_range *range)
{
        /* Sanity check this really should not happen. */
        if (range->hmm == NULL || range->end <= range->start)
                return;

        mutex_lock(&range->hmm->lock);
        list_del_rcu(&range->list);
        mutex_unlock(&range->hmm->lock);

        /* Drop reference taken by hmm_range_register() */
        range->valid = false;
        hmm_put(range->hmm);
        range->hmm = NULL;
}
EXPORT_SYMBOL(hmm_range_unregister);

/*
 * hmm_range_snapshot() - snapshot CPU page table for a range
 * @range: range
 * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
 *          permission (for instance asking for write and range is read only),
 *          -EAGAIN if you need to retry, -EFAULT invalid (ie either no valid
 *          vma or it is illegal to access that range), number of valid pages
 *          in range->pfns[] (from range start address).
 *
 * This snapshots the CPU page table for a range of virtual addresses. Snapshot
 * validity is tracked by range struct. See in include/linux/hmm.h for example
 * on how to use.
 */
long hmm_range_snapshot(struct hmm_range *range)
{
        const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;
        unsigned long start = range->start, end;
        struct hmm_vma_walk hmm_vma_walk;
        struct hmm *hmm = range->hmm;

        struct vm_area_struct *vma;
        struct mm_walk mm_walk;

        /* Check if hmm_mm_destroy() was call. */
        if (hmm->mm == NULL || hmm->dead)
                return -EFAULT;

        do {
                /* If range is no longer valid force retry. */
                if (!range->valid)
                        return -EAGAIN;

                vma = find_vma(hmm->mm, start);
                if (vma == NULL || (vma->vm_flags & device_vma))
                        return -EFAULT;

                if (is_vm_hugetlb_page(vma)) {
                        struct hstate *h = hstate_vma(vma);

                        if (huge_page_shift(h) != range->page_shift &&
                            range->page_shift != PAGE_SHIFT)
                                return -EINVAL;
                } else {
                        if (range->page_shift != PAGE_SHIFT)
                                return -EINVAL;
                }

                if (!(vma->vm_flags & VM_READ)) {
                        /*
                         * If vma do not allow read access, then assume that it
                         * does not allow write access, either. HMM does not
                         * support architecture that allow write without read.
                         */
                        hmm_pfns_clear(range, range->pfns,
                                range->start, range->end);
                        return -EPERM;
                }

                range->vma = vma;
                hmm_vma_walk.pgmap = NULL;
                hmm_vma_walk.last = start;
                hmm_vma_walk.fault = false;
                hmm_vma_walk.range = range;
                mm_walk.private = &hmm_vma_walk;
                end = min(range->end, vma->vm_end);

                mm_walk.vma = vma;
                mm_walk.mm = vma->vm_mm;
                mm_walk.pte_entry = NULL;
                mm_walk.test_walk = NULL;
                mm_walk.hugetlb_entry = NULL;
                mm_walk.pud_entry = hmm_vma_walk_pud;
                mm_walk.pmd_entry = hmm_vma_walk_pmd;
                mm_walk.pte_hole = hmm_vma_walk_hole;
                mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;

                walk_page_range(start, end, &mm_walk);
                start = end;
        } while (start < range->end);

        return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
}
EXPORT_SYMBOL(hmm_range_snapshot);

/*
 * hmm_range_fault() - try to fault some address in a virtual address range
 * @range: range being faulted
 * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
 * Returns: number of valid pages in range->pfns[] (from range start
 *          address). This may be zero. If the return value is negative,
 *          then one of the following values may be returned:
 *
 *           -EINVAL  invalid arguments or mm or virtual address are in an
 *                    invalid vma (for instance device file vma).
 *           -ENOMEM: Out of memory.
 *           -EPERM:  Invalid permission (for instance asking for write and
 *                    range is read only).
 *           -EAGAIN: If you need to retry and mmap_sem was drop. This can only
 *                    happens if block argument is false.
 *           -EBUSY:  If the the range is being invalidated and you should wait
 *                    for invalidation to finish.
 *           -EFAULT: Invalid (ie either no valid vma or it is illegal to access
 *                    that range), number of valid pages in range->pfns[] (from
 *                    range start address).
 *
 * This is similar to a regular CPU page fault except that it will not trigger
 * any memory migration if the memory being faulted is not accessible by CPUs
 * and caller does not ask for migration.
 *
 * On error, for one virtual address in the range, the function will mark the
 * corresponding HMM pfn entry with an error flag.
 */
long hmm_range_fault(struct hmm_range *range, bool block)
{
        const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;
        unsigned long start = range->start, end;
        struct hmm_vma_walk hmm_vma_walk;
        struct hmm *hmm = range->hmm;
        struct vm_area_struct *vma;
        struct mm_walk mm_walk;
        int ret;

        /* Check if hmm_mm_destroy() was call. */
        if (hmm->mm == NULL || hmm->dead)
                return -EFAULT;

        do {
                /* If range is no longer valid force retry. */
                if (!range->valid) {
                        up_read(&hmm->mm->mmap_sem);
                        return -EAGAIN;
                }

                vma = find_vma(hmm->mm, start);
                if (vma == NULL || (vma->vm_flags & device_vma))
                        return -EFAULT;

                if (is_vm_hugetlb_page(vma)) {
                        if (huge_page_shift(hstate_vma(vma)) !=
                            range->page_shift &&
                            range->page_shift != PAGE_SHIFT)
                                return -EINVAL;
                } else {
                        if (range->page_shift != PAGE_SHIFT)
                                return -EINVAL;
                }

                if (!(vma->vm_flags & VM_READ)) {
                        /*
                         * If vma do not allow read access, then assume that it
                         * does not allow write access, either. HMM does not
                         * support architecture that allow write without read.
                         */
                        hmm_pfns_clear(range, range->pfns,
                                range->start, range->end);
                        return -EPERM;
                }

                range->vma = vma;
                hmm_vma_walk.pgmap = NULL;
                hmm_vma_walk.last = start;
                hmm_vma_walk.fault = true;
                hmm_vma_walk.block = block;
                hmm_vma_walk.range = range;
                mm_walk.private = &hmm_vma_walk;
                end = min(range->end, vma->vm_end);

                mm_walk.vma = vma;
                mm_walk.mm = vma->vm_mm;
                mm_walk.pte_entry = NULL;
                mm_walk.test_walk = NULL;
                mm_walk.hugetlb_entry = NULL;
                mm_walk.pud_entry = hmm_vma_walk_pud;
                mm_walk.pmd_entry = hmm_vma_walk_pmd;
                mm_walk.pte_hole = hmm_vma_walk_hole;
                mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;

                do {
                        ret = walk_page_range(start, end, &mm_walk);
                        start = hmm_vma_walk.last;

                        /* Keep trying while the range is valid. */
                } while (ret == -EBUSY && range->valid);

                if (ret) {
                        unsigned long i;

                        i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
                        hmm_pfns_clear(range, &range->pfns[i],
                                hmm_vma_walk.last, range->end);
                        return ret;
                }
                start = end;

        } while (start < range->end);

        return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
}
EXPORT_SYMBOL(hmm_range_fault);

/**
 * hmm_range_dma_map() - hmm_range_fault() and dma map page all in one.
 * @range: range being faulted
 * @device: device against to dma map page to
 * @daddrs: dma address of mapped pages
 * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
 * Returns: number of pages mapped on success, -EAGAIN if mmap_sem have been
 *          drop and you need to try again, some other error value otherwise
 *
 * Note same usage pattern as hmm_range_fault().
 */
long hmm_range_dma_map(struct hmm_range *range,
                       struct device *device,
                       dma_addr_t *daddrs,
                       bool block)
{
        unsigned long i, npages, mapped;
        long ret;

        ret = hmm_range_fault(range, block);
        if (ret <= 0)
                return ret ? ret : -EBUSY;

        npages = (range->end - range->start) >> PAGE_SHIFT;
        for (i = 0, mapped = 0; i < npages; ++i) {
                enum dma_data_direction dir = DMA_TO_DEVICE;
                struct page *page;

                /*
                 * FIXME need to update DMA API to provide invalid DMA address
                 * value instead of a function to test dma address value. This
                 * would remove lot of dumb code duplicated accross many arch.
                 *
                 * For now setting it to 0 here is good enough as the pfns[]
                 * value is what is use to check what is valid and what isn't.
                 */
                daddrs[i] = 0;

                page = hmm_device_entry_to_page(range, range->pfns[i]);
                if (page == NULL)
                        continue;

                /* Check if range is being invalidated */
                if (!range->valid) {
                        ret = -EBUSY;
                        goto unmap;
                }

                /* If it is read and write than map bi-directional. */
                if (range->pfns[i] & range->flags[HMM_PFN_WRITE])
                        dir = DMA_BIDIRECTIONAL;

                daddrs[i] = dma_map_page(device, page, 0, PAGE_SIZE, dir);
                if (dma_mapping_error(device, daddrs[i])) {
                        ret = -EFAULT;
                        goto unmap;
                }

                mapped++;
        }

        return mapped;

unmap:
        for (npages = i, i = 0; (i < npages) && mapped; ++i) {
                enum dma_data_direction dir = DMA_TO_DEVICE;
                struct page *page;

                page = hmm_device_entry_to_page(range, range->pfns[i]);
                if (page == NULL)
                        continue;

                if (dma_mapping_error(device, daddrs[i]))
                        continue;

                /* If it is read and write than map bi-directional. */
                if (range->pfns[i] & range->flags[HMM_PFN_WRITE])
                        dir = DMA_BIDIRECTIONAL;

                dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
                mapped--;
        }

        return ret;
}
EXPORT_SYMBOL(hmm_range_dma_map);

/**
 * hmm_range_dma_unmap() - unmap range of that was map with hmm_range_dma_map()
 * @range: range being unmapped
 * @vma: the vma against which the range (optional)
 * @device: device against which dma map was done
 * @daddrs: dma address of mapped pages
 * @dirty: dirty page if it had the write flag set
 * Returns: number of page unmapped on success, -EINVAL otherwise
 *
 * Note that caller MUST abide by mmu notifier or use HMM mirror and abide
 * to the sync_cpu_device_pagetables() callback so that it is safe here to
 * call set_page_dirty(). Caller must also take appropriate locks to avoid
 * concurrent mmu notifier or sync_cpu_device_pagetables() to make progress.
 */
long hmm_range_dma_unmap(struct hmm_range *range,
                         struct vm_area_struct *vma,
                         struct device *device,
                         dma_addr_t *daddrs,
                         bool dirty)
{
        unsigned long i, npages;
        long cpages = 0;

        /* Sanity check. */
        if (range->end <= range->start)
                return -EINVAL;
        if (!daddrs)
                return -EINVAL;
        if (!range->pfns)
                return -EINVAL;

        npages = (range->end - range->start) >> PAGE_SHIFT;
        for (i = 0; i < npages; ++i) {
                enum dma_data_direction dir = DMA_TO_DEVICE;
                struct page *page;

                page = hmm_device_entry_to_page(range, range->pfns[i]);
                if (page == NULL)
                        continue;

                /* If it is read and write than map bi-directional. */
                if (range->pfns[i] & range->flags[HMM_PFN_WRITE]) {
                        dir = DMA_BIDIRECTIONAL;

                        /*
                         * See comments in function description on why it is
                         * safe here to call set_page_dirty()
                         */
                        if (dirty)
                                set_page_dirty(page);
                }

                /* Unmap and clear pfns/dma address */
                dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
                range->pfns[i] = range->values[HMM_PFN_NONE];
                /* FIXME see comments in hmm_vma_dma_map() */
                daddrs[i] = 0;
                cpages++;
        }

        return cpages;
}
EXPORT_SYMBOL(hmm_range_dma_unmap);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */


#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
                                       unsigned long addr)
{
        struct page *page;

        page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
        if (!page)
                return NULL;
        lock_page(page);
        return page;
}
EXPORT_SYMBOL(hmm_vma_alloc_locked_page);


static void hmm_devmem_ref_release(struct percpu_ref *ref)
{
        struct hmm_devmem *devmem;

        devmem = container_of(ref, struct hmm_devmem, ref);
        complete(&devmem->completion);
}

static void hmm_devmem_ref_exit(struct percpu_ref *ref)
{
        struct hmm_devmem *devmem;

        devmem = container_of(ref, struct hmm_devmem, ref);
        wait_for_completion(&devmem->completion);
        percpu_ref_exit(ref);
}

static void hmm_devmem_ref_kill(struct percpu_ref *ref)
{
        percpu_ref_kill(ref);
}

static vm_fault_t hmm_devmem_fault(struct vm_area_struct *vma,
                            unsigned long addr,
                            const struct page *page,
                            unsigned int flags,
                            pmd_t *pmdp)
{
        struct hmm_devmem *devmem = page->pgmap->data;

        return devmem->ops->fault(devmem, vma, addr, page, flags, pmdp);
}

static void hmm_devmem_free(struct page *page, void *data)
{
        struct hmm_devmem *devmem = data;

        page->mapping = NULL;

        devmem->ops->free(devmem, page);
}

/*
 * hmm_devmem_add() - hotplug ZONE_DEVICE memory for device memory
 *
 * @ops: memory event device driver callback (see struct hmm_devmem_ops)
 * @device: device struct to bind the resource too
 * @size: size in bytes of the device memory to add
 * Returns: pointer to new hmm_devmem struct ERR_PTR otherwise
 *
 * This function first finds an empty range of physical address big enough to
 * contain the new resource, and then hotplugs it as ZONE_DEVICE memory, which
 * in turn allocates struct pages. It does not do anything beyond that; all
 * events affecting the memory will go through the various callbacks provided
 * by hmm_devmem_ops struct.
 *
 * Device driver should call this function during device initialization and
 * is then responsible of memory management. HMM only provides helpers.
 */
struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
                                  struct device *device,
                                  unsigned long size)
{
        struct hmm_devmem *devmem;
        resource_size_t addr;
        void *result;
        int ret;

        dev_pagemap_get_ops();

        devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
        if (!devmem)
                return ERR_PTR(-ENOMEM);

        init_completion(&devmem->completion);
        devmem->pfn_first = -1UL;
        devmem->pfn_last = -1UL;
        devmem->resource = NULL;
        devmem->device = device;
        devmem->ops = ops;

        ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
                              0, GFP_KERNEL);
        if (ret)
                return ERR_PTR(ret);

        size = ALIGN(size, PA_SECTION_SIZE);
        addr = min((unsigned long)iomem_resource.end,
                   (1UL << MAX_PHYSMEM_BITS) - 1);
        addr = addr - size + 1UL;

        /*
         * FIXME add a new helper to quickly walk resource tree and find free
         * range
         *
         * FIXME what about ioport_resource resource ?
         */
        for (; addr > size && addr >= iomem_resource.start; addr -= size) {
                ret = region_intersects(addr, size, 0, IORES_DESC_NONE);
                if (ret != REGION_DISJOINT)
                        continue;

                devmem->resource = devm_request_mem_region(device, addr, size,
                                                           dev_name(device));
                if (!devmem->resource)
                        return ERR_PTR(-ENOMEM);
                break;
        }
        if (!devmem->resource)
                return ERR_PTR(-ERANGE);

        devmem->resource->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
        devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
        devmem->pfn_last = devmem->pfn_first +
                           (resource_size(devmem->resource) >> PAGE_SHIFT);
        devmem->page_fault = hmm_devmem_fault;

        devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
        devmem->pagemap.res = *devmem->resource;
        devmem->pagemap.page_free = hmm_devmem_free;
        devmem->pagemap.altmap_valid = false;
        devmem->pagemap.ref = &devmem->ref;
        devmem->pagemap.data = devmem;
        devmem->pagemap.kill = hmm_devmem_ref_kill;
        devmem->pagemap.cleanup = hmm_devmem_ref_exit;

        result = devm_memremap_pages(devmem->device, &devmem->pagemap);
        if (IS_ERR(result))
                return result;
        return devmem;
}
EXPORT_SYMBOL_GPL(hmm_devmem_add);

struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
                                           struct device *device,
                                           struct resource *res)
{
        struct hmm_devmem *devmem;
        void *result;
        int ret;

        if (res->desc != IORES_DESC_DEVICE_PUBLIC_MEMORY)
                return ERR_PTR(-EINVAL);

        dev_pagemap_get_ops();

        devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
        if (!devmem)
                return ERR_PTR(-ENOMEM);

        init_completion(&devmem->completion);
        devmem->pfn_first = -1UL;
        devmem->pfn_last = -1UL;
        devmem->resource = res;
        devmem->device = device;
        devmem->ops = ops;

        ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
                              0, GFP_KERNEL);
        if (ret)
                return ERR_PTR(ret);

        devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
        devmem->pfn_last = devmem->pfn_first +
                           (resource_size(devmem->resource) >> PAGE_SHIFT);
        devmem->page_fault = hmm_devmem_fault;

        devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
        devmem->pagemap.res = *devmem->resource;
        devmem->pagemap.page_free = hmm_devmem_free;
        devmem->pagemap.altmap_valid = false;
        devmem->pagemap.ref = &devmem->ref;
        devmem->pagemap.data = devmem;
        devmem->pagemap.kill = hmm_devmem_ref_kill;
        devmem->pagemap.cleanup = hmm_devmem_ref_exit;

        result = devm_memremap_pages(devmem->device, &devmem->pagemap);
        if (IS_ERR(result))
                return result;
        return devmem;
}
EXPORT_SYMBOL_GPL(hmm_devmem_add_resource);

/*
 * A device driver that wants to handle multiple devices memory through a
 * single fake device can use hmm_device to do so. This is purely a helper
 * and it is not needed to make use of any HMM functionality.
 */
#define HMM_DEVICE_MAX 256

static DECLARE_BITMAP(hmm_device_mask, HMM_DEVICE_MAX);
static DEFINE_SPINLOCK(hmm_device_lock);
static struct class *hmm_device_class;
static dev_t hmm_device_devt;

static void hmm_device_release(struct device *device)
{
        struct hmm_device *hmm_device;

        hmm_device = container_of(device, struct hmm_device, device);
        spin_lock(&hmm_device_lock);
        clear_bit(hmm_device->minor, hmm_device_mask);
        spin_unlock(&hmm_device_lock);

        kfree(hmm_device);
}

struct hmm_device *hmm_device_new(void *drvdata)
{
        struct hmm_device *hmm_device;

        hmm_device = kzalloc(sizeof(*hmm_device), GFP_KERNEL);
        if (!hmm_device)
                return ERR_PTR(-ENOMEM);

        spin_lock(&hmm_device_lock);
        hmm_device->minor = find_first_zero_bit(hmm_device_mask, HMM_DEVICE_MAX);
        if (hmm_device->minor >= HMM_DEVICE_MAX) {
                spin_unlock(&hmm_device_lock);
                kfree(hmm_device);
                return ERR_PTR(-EBUSY);
        }
        set_bit(hmm_device->minor, hmm_device_mask);
        spin_unlock(&hmm_device_lock);

        dev_set_name(&hmm_device->device, "hmm_device%d", hmm_device->minor);
        hmm_device->device.devt = MKDEV(MAJOR(hmm_device_devt),
                                        hmm_device->minor);
        hmm_device->device.release = hmm_device_release;
        dev_set_drvdata(&hmm_device->device, drvdata);
        hmm_device->device.class = hmm_device_class;
        device_initialize(&hmm_device->device);

        return hmm_device;
}
EXPORT_SYMBOL(hmm_device_new);

void hmm_device_put(struct hmm_device *hmm_device)
{
        put_device(&hmm_device->device);
}
EXPORT_SYMBOL(hmm_device_put);

static int __init hmm_init(void)
{
        int ret;

        ret = alloc_chrdev_region(&hmm_device_devt, 0,
                                  HMM_DEVICE_MAX,
                                  "hmm_device");
        if (ret)
                return ret;

        hmm_device_class = class_create(THIS_MODULE, "hmm_device");
        if (IS_ERR(hmm_device_class)) {
                unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
                return PTR_ERR(hmm_device_class);
        }
        return 0;
}

device_initcall(hmm_init);
#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */