gup.c

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/*
 *  Lockless get_user_pages_fast for s390
 *
 *  Copyright IBM Corp. 2010
 *  Author(s): Martin Schwidefsky <[email protected]>
 */
#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;
}

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;
    }
}