/*
 * Lockless get_user_pages_fast for powerpc
 *
 * Copyright (C) 2008 Nick Piggin
 * Copyright (C) 2008 Novell Inc.
 */
#undef DEBUG

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/vmstat.h>
#include <linux/pagemap.h>
#include <linux/rwsem.h>
#include <asm/pgtable.h>

#ifdef __HAVE_ARCH_PTE_SPECIAL

static inline void get_huge_page_tail(struct page *page)
{
        /*
         * __split_huge_page_refcount() cannot run
         * from under us.
         */
        VM_BUG_ON(atomic_read(&page->_count) < 0);
        atomic_inc(&page->_count);
}

/*
 * The performance critical leaf functions are made noinline otherwise gcc
 * inlines everything into a single function which results in too much
 * register pressure.
 */
static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
                unsigned long end, int write, struct page **pages, int *nr)
{
        unsigned long mask, result;
        pte_t *ptep;

        result = _PAGE_PRESENT|_PAGE_USER;
        if (write)
                result |= _PAGE_RW;
        mask = result | _PAGE_SPECIAL;

        ptep = pte_offset_kernel(&pmd, addr);
        do {
                pte_t pte = *ptep;
                struct page *page;

                if ((pte_val(pte) & mask) != result)
                        return 0;
                VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
                page = pte_page(pte);
                if (!page_cache_get_speculative(page))
                        return 0;
                if (unlikely(pte_val(pte) != pte_val(*ptep))) {
                        put_page(page);
                        return 0;
                }
                if (PageTail(page))
                        get_huge_page_tail(page);
                pages[*nr] = page;
                (*nr)++;

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

        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);
                if (pmd_none(pmd))
                        return 0;
                if (is_hugepd(pmdp)) {
                        if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
                                        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_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 (is_hugepd(pudp)) {
                        if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
                                        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;
}

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 nr = 0;

        pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");

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

        if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
                                        start, len)))
                goto slow_irqon;

        pr_devel("  aligned: %lx .. %lx\n", start, end);

        /*
         * 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 from being freed on powerpc.
         *
         * So long as we atomically load page table pointers versus teardown,
         * we can follow the address down to the the page and take a ref on it.
         */
        local_irq_disable();

        pgdp = pgd_offset(mm, addr);
        do {
                pgd_t pgd = *pgdp;

                pr_devel("  %016lx: normal pgd %p\n", addr,
                         (void *)pgd_val(pgd));
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
                if (is_hugepd(pgdp)) {
                        if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
                                        addr, next, write, pages, &nr))
                                goto slow;
                } else 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;

        {
                int ret;

slow:
                local_irq_enable();
slow_irqon:
                pr_devel("  slow path ! nr = %d\n", nr);

                /* 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;
        }
}

#endif /* __HAVE_ARCH_PTE_SPECIAL */