mincore.c

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/*
 *  linux/mm/mincore.c
 *
 * Copyright (C) 1994-2006  Linus Torvalds
 */

/*
 * The mincore() system call.
 */
#include <linux/pagemap.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>

static void mincore_hugetlb_page_range(struct vm_area_struct *vma,
                unsigned long addr, unsigned long end,
                unsigned char *vec)
{
#ifdef CONFIG_HUGETLB_PAGE
    struct hstate *h;

    h = hstate_vma(vma);
    while (1) {
        unsigned char present;
        pte_t *ptep;
        /*
         * Huge pages are always in RAM for now, but
         * theoretically it needs to be checked.
         */
        ptep = huge_pte_offset(current->mm,
                       addr & huge_page_mask(h));
        present = ptep && !huge_pte_none(huge_ptep_get(ptep));
        while (1) {
            *vec = present;
            vec++;
            addr += PAGE_SIZE;
            if (addr == end)
                return;
            /* check hugepage border */
            if (!(addr & ~huge_page_mask(h)))
                break;
        }
    }
#else
    BUG();
#endif
}

/*
 * Later we can get more picky about what "in core" means precisely.
 * For now, simply check to see if the page is in the page cache,
 * and is up to date; i.e. that no page-in operation would be required
 * at this time if an application were to map and access this page.
 */
static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
{
    unsigned char present = 0;
    struct page *page;

    /*
     * When tmpfs swaps out a page from a file, any process mapping that
     * file will not get a swp_entry_t in its pte, but rather it is like
     * any other file mapping (ie. marked !present and faulted in with
     * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
     */
    page = find_get_page(mapping, pgoff);
#ifdef CONFIG_SWAP
    /* shmem/tmpfs may return swap: account for swapcache page too. */
    if (radix_tree_exceptional_entry(page)) {
        swp_entry_t swap = radix_to_swp_entry(page);
        page = find_get_page(&swapper_space, swap.val);
    }
#endif
    if (page) {
        present = PageUptodate(page);
        page_cache_release(page);
    }

    return present;
}

static void mincore_unmapped_range(struct vm_area_struct *vma,
                unsigned long addr, unsigned long end,
                unsigned char *vec)
{
    unsigned long nr = (end - addr) >> PAGE_SHIFT;
    int i;

    if (vma->vm_file) {
        pgoff_t pgoff;

        pgoff = linear_page_index(vma, addr);
        for (i = 0; i < nr; i++, pgoff++)
            vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
    } else {
        for (i = 0; i < nr; i++)
            vec[i] = 0;
    }
}

static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
            unsigned long addr, unsigned long end,
            unsigned char *vec)
{
    unsigned long next;
    spinlock_t *ptl;
    pte_t *ptep;

    ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
    do {
        pte_t pte = *ptep;
        pgoff_t pgoff;

        next = addr + PAGE_SIZE;
        if (pte_none(pte))
            mincore_unmapped_range(vma, addr, next, vec);
        else if (pte_present(pte))
            *vec = 1;
        else if (pte_file(pte)) {
            pgoff = pte_to_pgoff(pte);
            *vec = mincore_page(vma->vm_file->f_mapping, pgoff);
        } else { /* pte is a swap entry */
            swp_entry_t entry = pte_to_swp_entry(pte);

            if (is_migration_entry(entry)) {
                /* migration entries are always uptodate */
                *vec = 1;
            } else {
#ifdef CONFIG_SWAP
                pgoff = entry.val;
                *vec = mincore_page(&swapper_space, pgoff);
#else
                WARN_ON(1);
                *vec = 1;
#endif
            }
        }
        vec++;
    } while (ptep++, addr = next, addr != end);
    pte_unmap_unlock(ptep - 1, ptl);
}

static void mincore_pmd_range(struct vm_area_struct *vma, pud_t *pud,
            unsigned long addr, unsigned long end,
            unsigned char *vec)
{
    unsigned long next;
    pmd_t *pmd;

    pmd = pmd_offset(pud, addr);
    do {
        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*pmd)) {
            if (mincore_huge_pmd(vma, pmd, addr, next, vec)) {
                vec += (next - addr) >> PAGE_SHIFT;
                continue;
            }
            /* fall through */
        }
        if (pmd_none_or_trans_huge_or_clear_bad(pmd))
            mincore_unmapped_range(vma, addr, next, vec);
        else
            mincore_pte_range(vma, pmd, addr, next, vec);
        vec += (next - addr) >> PAGE_SHIFT;
    } while (pmd++, addr = next, addr != end);
}

static void mincore_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
            unsigned long addr, unsigned long end,
            unsigned char *vec)
{
    unsigned long next;
    pud_t *pud;

    pud = pud_offset(pgd, addr);
    do {
        next = pud_addr_end(addr, end);
        if (pud_none_or_clear_bad(pud))
            mincore_unmapped_range(vma, addr, next, vec);
        else
            mincore_pmd_range(vma, pud, addr, next, vec);
        vec += (next - addr) >> PAGE_SHIFT;
    } while (pud++, addr = next, addr != end);
}

static void mincore_page_range(struct vm_area_struct *vma,
            unsigned long addr, unsigned long end,
            unsigned char *vec)
{
    unsigned long next;
    pgd_t *pgd;

    pgd = pgd_offset(vma->vm_mm, addr);
    do {
        next = pgd_addr_end(addr, end);
        if (pgd_none_or_clear_bad(pgd))
            mincore_unmapped_range(vma, addr, next, vec);
        else
            mincore_pud_range(vma, pgd, addr, next, vec);
        vec += (next - addr) >> PAGE_SHIFT;
    } while (pgd++, addr = next, addr != end);
}

/*
 * Do a chunk of "sys_mincore()". We've already checked
 * all the arguments, we hold the mmap semaphore: we should
 * just return the amount of info we're asked for.
 */
static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
{
    struct vm_area_struct *vma;
    unsigned long end;

    vma = find_vma(current->mm, addr);
    if (!vma || addr < vma->vm_start)
        return -ENOMEM;

    end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));

    if (is_vm_hugetlb_page(vma)) {
        mincore_hugetlb_page_range(vma, addr, end, vec);
        return (end - addr) >> PAGE_SHIFT;
    }

    end = pmd_addr_end(addr, end);

    if (is_vm_hugetlb_page(vma))
        mincore_hugetlb_page_range(vma, addr, end, vec);
    else
        mincore_page_range(vma, addr, end, vec);

    return (end - addr) >> PAGE_SHIFT;
}

/*
 * The mincore(2) system call.
 *
 * mincore() returns the memory residency status of the pages in the
 * current process's address space specified by [addr, addr + len).
 * The status is returned in a vector of bytes.  The least significant
 * bit of each byte is 1 if the referenced page is in memory, otherwise
 * it is zero.
 *
 * Because the status of a page can change after mincore() checks it
 * but before it returns to the application, the returned vector may
 * contain stale information.  Only locked pages are guaranteed to
 * remain in memory.
 *
 * return values:
 *  zero    - success
 *  -EFAULT - vec points to an illegal address
 *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 *      invalid for the address space of this process, or
 *      specify one or more pages which are not currently
 *      mapped
 *  -EAGAIN - A kernel resource was temporarily unavailable.
 */
SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
        unsigned char __user *, vec)
{
    long retval;
    unsigned long pages;
    unsigned char *tmp;

    /* Check the start address: needs to be page-aligned.. */
    if (start & ~PAGE_CACHE_MASK)
        return -EINVAL;

    /* ..and we need to be passed a valid user-space range */
    if (!access_ok(VERIFY_READ, (void __user *) start, len))
        return -ENOMEM;

    /* This also avoids any overflows on PAGE_CACHE_ALIGN */
    pages = len >> PAGE_SHIFT;
    pages += (len & ~PAGE_MASK) != 0;

    if (!access_ok(VERIFY_WRITE, vec, pages))
        return -EFAULT;

    tmp = (void *) __get_free_page(GFP_USER);
    if (!tmp)
        return -EAGAIN;

    retval = 0;
    while (pages) {
        /*
         * Do at most PAGE_SIZE entries per iteration, due to
         * the temporary buffer size.
         */
        down_read(&current->mm->mmap_sem);
        retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
        up_read(&current->mm->mmap_sem);

        if (retval <= 0)
            break;
        if (copy_to_user(vec, tmp, retval)) {
            retval = -EFAULT;
            break;
        }
        pages -= retval;
        vec += retval;
        start += retval << PAGE_SHIFT;
        retval = 0;
    }
    free_page((unsigned long) tmp);
    return retval;
}