/*
 * Lockless get_user_pages_fast for MIPS
 *
 * Copyright (C) 2008 Nick Piggin
 * Copyright (C) 2008 Novell Inc.
 * Copyright (C) 2011 Ralf Baechle
 */
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/highmem.h>
#include <linux/swap.h>
#include <linux/hugetlb.h>

#include <asm/pgtable.h>

static inline pte_t gup_get_pte(pte_t *ptep)
{
#if defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32)
        pte_t pte;

retry:
        pte.pte_low = ptep->pte_low;
        smp_rmb();
        pte.pte_high = ptep->pte_high;
        smp_rmb();
        if (unlikely(pte.pte_low != ptep->pte_low))
                goto retry;

        return pte;
#else
        return ACCESS_ONCE(*ptep);
#endif
}

static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
                        int write, struct page **pages, int *nr)
{
        pte_t *ptep = pte_offset_map(&pmd, addr);
        do {
                pte_t pte = gup_get_pte(ptep);
                struct page *page;

                if (!pte_present(pte) ||
                    pte_special(pte) || (write && !pte_write(pte))) {
                        pte_unmap(ptep);
                        return 0;
                }
                VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
                page = pte_page(pte);
                get_page(page);
                SetPageReferenced(page);
                pages[*nr] = page;
                (*nr)++;

        } while (ptep++, addr += PAGE_SIZE, addr != end);

        pte_unmap(ptep - 1);
        return 1;
}

static inline void get_head_page_multiple(struct page *page, int nr)
{
        VM_BUG_ON(page != compound_head(page));
        VM_BUG_ON(page_count(page) == 0);
        atomic_add(nr, &page->_count);
        SetPageReferenced(page);
}

static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
                        int write, struct page **pages, int *nr)
{
        pte_t pte = *(pte_t *)&pmd;
        struct page *head, *page;
        int refs;

        if (write && !pte_write(pte))
                return 0;
        /* hugepages are never "special" */
        VM_BUG_ON(pte_special(pte));
        VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

        refs = 0;
        head = pte_page(pte);
        page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
        do {
                VM_BUG_ON(compound_head(page) != head);
                pages[*nr] = page;
                if (PageTail(page))
                        get_huge_page_tail(page);
                (*nr)++;
                page++;
                refs++;
        } while (addr += PAGE_SIZE, addr != end);

        get_head_page_multiple(head, refs);
        return 1;
}

static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
                        int write, struct page **pages, int *nr)
{
        unsigned long next;
        pmd_t *pmdp;

        pmdp = pmd_offset(&pud, addr);
        do {
                pmd_t pmd = *pmdp;

                next = pmd_addr_end(addr, end);
                /*
                 * The pmd_trans_splitting() check below explains why
                 * pmdp_splitting_flush has to flush the tlb, to stop
                 * this gup-fast code from running while we set the
                 * splitting bit in the pmd. Returning zero will take
                 * the slow path that will call wait_split_huge_page()
                 * if the pmd is still in splitting state. gup-fast
                 * can't because it has irq disabled and
                 * wait_split_huge_page() would never return as the
                 * tlb flush IPI wouldn't run.
                 */
                if (pmd_none(pmd) || pmd_trans_splitting(pmd))
                        return 0;
                if (unlikely(pmd_huge(pmd))) {
                        if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
                                return 0;
                } else {
                        if (!gup_pte_range(pmd, addr, next, write, pages,nr))
                                return 0;
                }
        } while (pmdp++, addr = next, addr != end);

        return 1;
}

static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
                        int write, struct page **pages, int *nr)
{
        pte_t pte = *(pte_t *)&pud;
        struct page *head, *page;
        int refs;

        if (write && !pte_write(pte))
                return 0;
        /* hugepages are never "special" */
        VM_BUG_ON(pte_special(pte));
        VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

        refs = 0;
        head = pte_page(pte);
        page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
        do {
                VM_BUG_ON(compound_head(page) != head);
                pages[*nr] = page;
                if (PageTail(page))
                        get_huge_page_tail(page);
                (*nr)++;
                page++;
                refs++;
        } while (addr += PAGE_SIZE, addr != end);

        get_head_page_multiple(head, refs);
        return 1;
}

static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
                        int write, struct page **pages, int *nr)
{
        unsigned long next;
        pud_t *pudp;

        pudp = pud_offset(&pgd, addr);
        do {
                pud_t pud = *pudp;

                next = pud_addr_end(addr, end);
                if (pud_none(pud))
                        return 0;
                if (unlikely(pud_huge(pud))) {
                        if (!gup_huge_pud(pud, addr, next, write, pages,nr))
                                return 0;
                } else {
                        if (!gup_pmd_range(pud, addr, next, write, pages,nr))
                                return 0;
                }
        } while (pudp++, addr = next, addr != end);

        return 1;
}

/*
 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 * back to the regular GUP.
 */
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
                          struct page **pages)
{
        struct mm_struct *mm = current->mm;
        unsigned long addr, len, end;
        unsigned long next;
        unsigned long flags;
        pgd_t *pgdp;
        int nr = 0;

        start &= PAGE_MASK;
        addr = start;
        len = (unsigned long) nr_pages << PAGE_SHIFT;
        end = start + len;
        if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
                                        (void __user *)start, len)))
                return 0;

        /*
         * XXX: batch / limit 'nr', to avoid large irq off latency
         * needs some instrumenting to determine the common sizes used by
         * important workloads (eg. DB2), and whether limiting the batch
         * size will decrease performance.
         *
         * It seems like we're in the clear for the moment. Direct-IO is
         * the main guy that batches up lots of get_user_pages, and even
         * they are limited to 64-at-a-time which is not so many.
         */
        /*
         * This doesn't prevent pagetable teardown, but does prevent
         * the pagetables and pages from being freed.
         *
         * So long as we atomically load page table pointers versus teardown,
         * we can follow the address down to the page and take a ref on it.
         */
        local_irq_save(flags);
        pgdp = pgd_offset(mm, addr);
        do {
                pgd_t pgd = *pgdp;

                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        break;
                if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
                        break;
        } while (pgdp++, addr = next, addr != end);
        local_irq_restore(flags);

        return nr;
}

/**
 * get_user_pages_fast() - pin user pages in memory
 * @start:      starting user address
 * @nr_pages:   number of pages from start to pin
 * @write:      whether pages will be written to
 * @pages:      array that receives pointers to the pages pinned.
 *              Should be at least nr_pages long.
 *
 * Attempt to pin user pages in memory without taking mm->mmap_sem.
 * If not successful, it will fall back to taking the lock and
 * calling get_user_pages().
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno.
 */
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                        struct page **pages)
{
        struct mm_struct *mm = current->mm;
        unsigned long addr, len, end;
        unsigned long next;
        pgd_t *pgdp;
        int ret, nr = 0;

        start &= PAGE_MASK;
        addr = start;
        len = (unsigned long) nr_pages << PAGE_SHIFT;

        end = start + len;
        if (end < start)
                goto slow_irqon;

        /* XXX: batch / limit 'nr' */
        local_irq_disable();
        pgdp = pgd_offset(mm, addr);
        do {
                pgd_t pgd = *pgdp;

                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
                if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
                        goto slow;
        } while (pgdp++, addr = next, addr != end);
        local_irq_enable();

        VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
        return nr;
slow:
        local_irq_enable();

slow_irqon:
        /* Try to get the remaining pages with get_user_pages */
        start += nr << PAGE_SHIFT;
        pages += nr;

        down_read(&mm->mmap_sem);
        ret = get_user_pages(current, mm, start,
                                (end - start) >> PAGE_SHIFT,
                                write, 0, pages, NULL);
        up_read(&mm->mmap_sem);

        /* Have to be a bit careful with return values */
        if (nr > 0) {
                if (ret < 0)
                        ret = nr;
                else
                        ret += nr;
        }
        return ret;
}