#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/sched.h>
#include <linux/hugetlb.h>

static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
                          struct mm_walk *walk)
{
        pte_t *pte;
        int err = 0;

        pte = pte_offset_map(pmd, addr);
        for (;;) {
                err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
                if (err)
                       break;
                addr += PAGE_SIZE;
                if (addr == end)
                        break;
                pte++;
        }

        pte_unmap(pte);
        return err;
}

static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
                          struct mm_walk *walk)
{
        pmd_t *pmd;
        unsigned long next;
        int err = 0;

        pmd = pmd_offset(pud, addr);
        do {
again:
                next = pmd_addr_end(addr, end);
                if (pmd_none(*pmd) || !walk->vma) {
                        if (walk->pte_hole)
                                err = walk->pte_hole(addr, next, walk);
                        if (err)
                                break;
                        continue;
                }
                /*
                 * This implies that each ->pmd_entry() handler
                 * needs to know about pmd_trans_huge() pmds
                 */
                if (walk->pmd_entry)
                        err = walk->pmd_entry(pmd, addr, next, walk);
                if (err)
                        break;

                /*
                 * Check this here so we only break down trans_huge
                 * pages when we _need_ to
                 */
                if (!walk->pte_entry)
                        continue;

                split_huge_pmd(walk->vma, pmd, addr);
                if (pmd_trans_unstable(pmd))
                        goto again;
                err = walk_pte_range(pmd, addr, next, walk);
                if (err)
                        break;
        } while (pmd++, addr = next, addr != end);

        return err;
}

static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,
                          struct mm_walk *walk)
{
        pud_t *pud;
        unsigned long next;
        int err = 0;

        pud = pud_offset(pgd, addr);
        do {
                next = pud_addr_end(addr, end);
                if (pud_none_or_clear_bad(pud)) {
                        if (walk->pte_hole)
                                err = walk->pte_hole(addr, next, walk);
                        if (err)
                                break;
                        continue;
                }
                if (walk->pmd_entry || walk->pte_entry)
                        err = walk_pmd_range(pud, addr, next, walk);
                if (err)
                        break;
        } while (pud++, addr = next, addr != end);

        return err;
}

static int walk_pgd_range(unsigned long addr, unsigned long end,
                          struct mm_walk *walk)
{
        pgd_t *pgd;
        unsigned long next;
        int err = 0;

        pgd = pgd_offset(walk->mm, addr);
        do {
                next = pgd_addr_end(addr, end);
                if (pgd_none_or_clear_bad(pgd)) {
                        if (walk->pte_hole)
                                err = walk->pte_hole(addr, next, walk);
                        if (err)
                                break;
                        continue;
                }
                if (walk->pmd_entry || walk->pte_entry)
                        err = walk_pud_range(pgd, addr, next, walk);
                if (err)
                        break;
        } while (pgd++, addr = next, addr != end);

        return err;
}

#ifdef CONFIG_HUGETLB_PAGE
static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
                                       unsigned long end)
{
        unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
        return boundary < end ? boundary : end;
}

static int walk_hugetlb_range(unsigned long addr, unsigned long end,
                              struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->vma;
        struct hstate *h = hstate_vma(vma);
        unsigned long next;
        unsigned long hmask = huge_page_mask(h);
        pte_t *pte;
        int err = 0;

        do {
                next = hugetlb_entry_end(h, addr, end);
                pte = huge_pte_offset(walk->mm, addr & hmask);
                if (pte && walk->hugetlb_entry)
                        err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
                if (err)
                        break;
        } while (addr = next, addr != end);

        return err;
}

#else /* CONFIG_HUGETLB_PAGE */
static int walk_hugetlb_range(unsigned long addr, unsigned long end,
                              struct mm_walk *walk)
{
        return 0;
}

#endif /* CONFIG_HUGETLB_PAGE */

/*
 * Decide whether we really walk over the current vma on [@start, @end)
 * or skip it via the returned value. Return 0 if we do walk over the
 * current vma, and return 1 if we skip the vma. Negative values means
 * error, where we abort the current walk.
 */
static int walk_page_test(unsigned long start, unsigned long end,
                        struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->vma;

        if (walk->test_walk)
                return walk->test_walk(start, end, walk);

        /*
         * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
         * range, so we don't walk over it as we do for normal vmas. However,
         * Some callers are interested in handling hole range and they don't
         * want to just ignore any single address range. Such users certainly
         * define their ->pte_hole() callbacks, so let's delegate them to handle
         * vma(VM_PFNMAP).
         */
        if (vma->vm_flags & VM_PFNMAP) {
                int err = 1;
                if (walk->pte_hole)
                        err = walk->pte_hole(start, end, walk);
                return err ? err : 1;
        }
        return 0;
}

static int __walk_page_range(unsigned long start, unsigned long end,
                        struct mm_walk *walk)
{
        int err = 0;
        struct vm_area_struct *vma = walk->vma;

        if (vma && is_vm_hugetlb_page(vma)) {
                if (walk->hugetlb_entry)
                        err = walk_hugetlb_range(start, end, walk);
        } else
                err = walk_pgd_range(start, end, walk);

        return err;
}

/**
 * walk_page_range - walk page table with caller specific callbacks
 *
 * Recursively walk the page table tree of the process represented by @walk->mm
 * within the virtual address range [@start, @end). During walking, we can do
 * some caller-specific works for each entry, by setting up pmd_entry(),
 * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
 * callbacks, the associated entries/pages are just ignored.
 * The return values of these callbacks are commonly defined like below:
 *  - 0  : succeeded to handle the current entry, and if you don't reach the
 *         end address yet, continue to walk.
 *  - >0 : succeeded to handle the current entry, and return to the caller
 *         with caller specific value.
 *  - <0 : failed to handle the current entry, and return to the caller
 *         with error code.
 *
 * Before starting to walk page table, some callers want to check whether
 * they really want to walk over the current vma, typically by checking
 * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
 * purpose.
 *
 * struct mm_walk keeps current values of some common data like vma and pmd,
 * which are useful for the access from callbacks. If you want to pass some
 * caller-specific data to callbacks, @walk->private should be helpful.
 *
 * Locking:
 *   Callers of walk_page_range() and walk_page_vma() should hold
 *   @walk->mm->mmap_sem, because these function traverse vma list and/or
 *   access to vma's data.
 */
int walk_page_range(unsigned long start, unsigned long end,
                    struct mm_walk *walk)
{
        int err = 0;
        unsigned long next;
        struct vm_area_struct *vma;

        if (start >= end)
                return -EINVAL;

        if (!walk->mm)
                return -EINVAL;

        VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);

        vma = find_vma(walk->mm, start);
        do {
                if (!vma) { /* after the last vma */
                        walk->vma = NULL;
                        next = end;
                } else if (start < vma->vm_start) { /* outside vma */
                        walk->vma = NULL;
                        next = min(end, vma->vm_start);
                } else { /* inside vma */
                        walk->vma = vma;
                        next = min(end, vma->vm_end);
                        vma = vma->vm_next;

                        err = walk_page_test(start, next, walk);
                        if (err > 0) {
                                /*
                                 * positive return values are purely for
                                 * controlling the pagewalk, so should never
                                 * be passed to the callers.
                                 */
                                err = 0;
                                continue;
                        }
                        if (err < 0)
                                break;
                }
                if (walk->vma || walk->pte_hole)
                        err = __walk_page_range(start, next, walk);
                if (err)
                        break;
        } while (start = next, start < end);
        return err;
}

int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
{
        int err;

        if (!walk->mm)
                return -EINVAL;

        VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
        VM_BUG_ON(!vma);
        walk->vma = vma;
        err = walk_page_test(vma->vm_start, vma->vm_end, walk);
        if (err > 0)
                return 0;
        if (err < 0)
                return err;
        return __walk_page_range(vma->vm_start, vma->vm_end, walk);
}