/*
 * 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

/*
 * 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;
                }
                pages[*nr] = page;
                (*nr)++;

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

        return 1;
}

#ifdef CONFIG_HUGETLB_PAGE
static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
                                 unsigned long *addr, unsigned long end,
                                 int write, struct page **pages, int *nr)
{
        unsigned long mask;
        unsigned long pte_end;
        struct page *head, *page;
        pte_t pte;
        int refs;

        pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
        if (pte_end < end)
                end = pte_end;

        pte = *ptep;
        mask = _PAGE_PRESENT|_PAGE_USER;
        if (write)
                mask |= _PAGE_RW;
        if ((pte_val(pte) & mask) != mask)
                return 0;
        /* hugepages are never "special" */
        VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

        refs = 0;
        head = pte_page(pte);
        page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
        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(pte_val(pte) != pte_val(*ptep))) {
                /* Could be optimized better */
                while (*nr) {
                        put_page(page);
                        (*nr)--;
                }
        }

        return 1;
}
#endif /* CONFIG_HUGETLB_PAGE */

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 (!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;
        pgd_t *pgdp;
        int nr = 0;
#ifdef CONFIG_PPC64
        unsigned int shift;
        int psize;
#endif

        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);

#ifdef CONFIG_HUGETLB_PAGE
        /* We bail out on slice boundary crossing when hugetlb is
         * enabled in order to not have to deal with two different
         * page table formats
         */
        if (addr < SLICE_LOW_TOP) {
                if (end > SLICE_LOW_TOP)
                        goto slow_irqon;

                if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
                             GET_LOW_SLICE_INDEX(end - 1)))
                        goto slow_irqon;
        } else {
                if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
                             GET_HIGH_SLICE_INDEX(end - 1)))
                        goto slow_irqon;
        }
#endif /* CONFIG_HUGETLB_PAGE */

        /*
         * 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();

#ifdef CONFIG_PPC64
        /* Those bits are related to hugetlbfs implementation and only exist
         * on 64-bit for now
         */
        psize = get_slice_psize(mm, addr);
        shift = mmu_psize_defs[psize].shift;
#endif /* CONFIG_PPC64 */

#ifdef CONFIG_HUGETLB_PAGE
        if (unlikely(mmu_huge_psizes[psize])) {
                pte_t *ptep;
                unsigned long a = addr;
                unsigned long sz = ((1UL) << shift);
                struct hstate *hstate = size_to_hstate(sz);

                BUG_ON(!hstate);
                /*
                 * XXX: could be optimized to avoid hstate
                 * lookup entirely (just use shift)
                 */

                do {
                        VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
                        ptep = huge_pte_offset(mm, a);
                        pr_devel(" %016lx: huge ptep %p\n", a, ptep);
                        if (!ptep || !gup_huge_pte(ptep, hstate, &a, end, write, pages,
                                                   &nr))
                                goto slow;
                } while (a != end);
        } else
#endif /* CONFIG_HUGETLB_PAGE */
        {
                pgdp = pgd_offset(mm, addr);
                do {
                        pgd_t pgd = *pgdp;

#ifdef CONFIG_PPC64
                        VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
#endif
                        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 (!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 */