/*
 * Lockless get_user_pages_fast for sparc, cribbed from powerpc
 *
 * Copyright (C) 2008 Nick Piggin
 * Copyright (C) 2008 Novell Inc.
 */

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

/*
 * 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;

        if (tlb_type == hypervisor) {
                result = _PAGE_PRESENT_4V|_PAGE_P_4V;
                if (write)
                        result |= _PAGE_WRITE_4V;
        } else {
                result = _PAGE_PRESENT_4U|_PAGE_P_4U;
                if (write)
                        result |= _PAGE_WRITE_4U;
        }
        mask = result | _PAGE_SPECIAL;

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

                if ((pte_val(pte) & mask) != result)
                        return 0;
                VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

                /* The hugepage case is simplified on sparc64 because
                 * we encode the sub-page pfn offsets into the
                 * hugepage PTEs.  We could optimize this in the future
                 * use page_cache_add_speculative() for the hugepage case.
                 */
                page = pte_page(pte);
                head = compound_head(page);
                if (!page_cache_get_speculative(head))
                        return 0;
                if (unlikely(pte_val(pte) != pte_val(*ptep))) {
                        put_page(head);
                        return 0;
                }
                if (head != page)
                        get_huge_page_tail(page);

                pages[*nr] = page;
                (*nr)++;
        } while (ptep++, addr += PAGE_SIZE, addr != end);

        return 1;
}

static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
                        unsigned long end, int write, struct page **pages,
                        int *nr)
{
        struct page *head, *page, *tail;
        int refs;

        if (!(pmd_val(pmd) & _PAGE_VALID))
                return 0;

        if (write && !pmd_write(pmd))
                return 0;

        refs = 0;
        head = pmd_page(pmd);
        page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
        tail = page;
        do {
                VM_BUG_ON(compound_head(page) != head);
                pages[*nr] = page;
                (*nr)++;
                page++;
                refs++;
        } while (addr += PAGE_SIZE, addr != end);

        if (!page_cache_add_speculative(head, refs)) {
                *nr -= refs;
                return 0;
        }

        if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
                *nr -= refs;
                while (refs--)
                        put_page(head);
                return 0;
        }

        /* Any tail page need their mapcount reference taken before we
         * return.
         */
        while (refs--) {
                if (PageTail(tail))
                        get_huge_page_tail(tail);
                tail++;
        }

        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) || pmd_trans_splitting(pmd))
                        return 0;
                if (unlikely(pmd_large(pmd))) {
                        if (!gup_huge_pmd(pmdp, 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_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 (!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, flags;
        pgd_t *pgdp;
        int nr = 0;

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

        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;
}

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;

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

        /*
         * 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 sparc.
         *
         * 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;

                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;

        {
                int ret;

slow:
                local_irq_enable();

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

                ret = get_user_pages_unlocked(current, mm, start,
                        (end - start) >> PAGE_SHIFT, write, 0, pages);

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

                return ret;
        }
}