/*
 *  Lockless get_user_pages_fast for s390
 *
 *  Copyright IBM Corp. 2010
 *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
 */
#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>

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

        mask = (write ? _PAGE_RO : 0) | _PAGE_INVALID | _PAGE_SPECIAL;

        ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
        do {
                pte = *ptep;
                barrier();
                if ((pte_val(pte) & mask) != 0)
                        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;
}

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

        result = write ? 0 : _SEGMENT_ENTRY_RO;
        mask = result | _SEGMENT_ENTRY_INV;
        if ((pmd_val(pmd) & mask) != result)
                return 0;
        VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));

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

        pmdp = (pmd_t *) pudp;
#ifdef CONFIG_64BIT
        if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
                pmdp = (pmd_t *) pud_deref(pud);
        pmdp += pmd_index(addr);
#endif
        do {
                pmd = *pmdp;
                barrier();
                next = pmd_addr_end(addr, end);
                /*
                 * The pmd_trans_splitting() check below explains why
                 * pmdp_splitting_flush() has to serialize with
                 * smp_call_function() against our disabled IRQs, 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.
                 */
                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(pmdp, pmd, addr, next,
                                          write, pages, nr))
                        return 0;
        } while (pmdp++, addr = next, addr != end);

        return 1;
}

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

        pudp = (pud_t *) pgdp;
#ifdef CONFIG_64BIT
        if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
                pudp = (pud_t *) pgd_deref(pgd);
        pudp += pud_index(addr);
#endif
        do {
                pud = *pudp;
                barrier();
                next = pud_addr_end(addr, end);
                if (pud_none(pud))
                        return 0;
                if (!gup_pmd_range(pudp, 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, flags;
        pgd_t *pgdp, pgd;
        int nr = 0;

        start &= PAGE_MASK;
        addr = start;
        len = (unsigned long) nr_pages << PAGE_SHIFT;
        end = start + len;
        if ((end < start) || (end > TASK_SIZE))
                return 0;

        local_irq_save(flags);
        pgdp = pgd_offset(mm, addr);
        do {
                pgd = *pgdp;
                barrier();
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        break;
                if (!gup_pud_range(pgdp, 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, pgd;
        int nr = 0;

        start &= PAGE_MASK;
        addr = start;
        len = (unsigned long) nr_pages << PAGE_SHIFT;
        end = start + len;
        if ((end < start) || (end > TASK_SIZE))
                goto slow_irqon;

        /*
         * local_irq_disable() doesn't prevent pagetable teardown, but does
         * prevent the pagetables from being freed on s390.
         *
         * 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 = *pgdp;
                barrier();
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
                if (!gup_pud_range(pgdp, 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:
                /* 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;
        }
}