/*
 *      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.
         *
         * However when tmpfs moves the page from pagecache and into swapcache,
         * it is still in core, but the find_get_page below won't find it.
         * No big deal, but make a note of it.
         */
        page = find_get_page(mapping, pgoff);
        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_none_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;
}