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/*

 *   linux/mm/fremap.c

 *

 * Explicit pagetable population and nonlinear (random) mappings support.

 *

 * started by Ingo Molnar, Copyright (C) 2002, 2003

 */

#include <linux/backing-dev.h>

#include <linux/mm.h>

#include <linux/swap.h>

#include <linux/file.h>

#include <linux/mman.h>

#include <linux/pagemap.h>

#include <linux/swapops.h>

#include <linux/rmap.h>

#include <linux/module.h>

#include <linux/syscalls.h>

#include <asm/mmu_context.h>

#include <asm/cacheflush.h>

#include <asm/tlbflush.h>

static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,

                        unsigned long addr, pte_t *ptep)

{

        pte_t pte = *ptep;

        if (pte_present(pte)) {

                struct page *page;

                flush_cache_page(vma, addr, pte_pfn(pte));

                pte = ptep_clear_flush(vma, addr, ptep);

                page = vm_normal_page(vma, addr, pte);

                if (page) {

                        if (pte_dirty(pte))

                                set_page_dirty(page);

                        page_remove_rmap(page, vma);

                        page_cache_release(page);

                        update_hiwater_rss(mm);

                        dec_mm_counter(mm, file_rss);

                }

        } else {

                if (!pte_file(pte))

                        free_swap_and_cache(pte_to_swp_entry(pte));

                pte_clear_not_present_full(mm, addr, ptep, 0);

        }

}

/*

 * Install a file pte to a given virtual memory address, release any

 * previously existing mapping.

 */

static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,

                unsigned long addr, unsigned long pgoff, pgprot_t prot)

{

        int err = -ENOMEM;

        pte_t *pte;

        spinlock_t *ptl;

        pte = get_locked_pte(mm, addr, &ptl);

        if (!pte)

                goto out;

        if (!pte_none(*pte))

                zap_pte(mm, vma, addr, pte);

        set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));

        /*

         * We don't need to run update_mmu_cache() here because the "file pte"

         * being installed by install_file_pte() is not a real pte - it's a

         * non-present entry (like a swap entry), noting what file offset should

         * be mapped there when there's a fault (in a non-linear vma where

         * that's not obvious).

         */

        pte_unmap_unlock(pte, ptl);

        err = 0;

out:

        return err;

}

static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,

                        unsigned long addr, unsigned long size, pgoff_t pgoff)

{

        int err;

        do {

                err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);

                if (err)

                        return err;

                size -= PAGE_SIZE;

                addr += PAGE_SIZE;

                pgoff++;

        } while (size);

        return 0;

}

/**

 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma

 * @start: start of the remapped virtual memory range

 * @size: size of the remapped virtual memory range

 * @prot: new protection bits of the range (see NOTE)

 * @pgoff: to-be-mapped page of the backing store file

 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.

 *

 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma

 * (shared backing store file).

 *

 * This syscall works purely via pagetables, so it's the most efficient

 * way to map the same (large) file into a given virtual window. Unlike

 * mmap()/mremap() it does not create any new vmas. The new mappings are

 * also safe across swapout.

 *

 * NOTE: the 'prot' parameter right now is ignored (but must be zero),

 * and the vma's default protection is used. Arbitrary protections

 * might be implemented in the future.

 */

asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,

        unsigned long prot, unsigned long pgoff, unsigned long flags)

{

        struct mm_struct *mm = current->mm;

        struct address_space *mapping;

        unsigned long end = start + size;

        struct vm_area_struct *vma;

        int err = -EINVAL;

        int has_write_lock = 0;

        if (prot)

                return err;

        /*

         * Sanitize the syscall parameters:

         */

        start = start & PAGE_MASK;

        size = size & PAGE_MASK;

        /* Does the address range wrap, or is the span zero-sized? */

        if (start + size <= start)

                return err;

        /* Can we represent this offset inside this architecture's pte's? */

#if PTE_FILE_MAX_BITS < BITS_PER_LONG

        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))

                return err;

#endif

        /* We need down_write() to change vma->vm_flags. */

        down_read(&mm->mmap_sem);

 retry:

        vma = find_vma(mm, start);

        /*

         * Make sure the vma is shared, that it supports prefaulting,

         * and that the remapped range is valid and fully within

         * the single existing vma.  vm_private_data is used as a

         * swapout cursor in a VM_NONLINEAR vma.

         */

        if (!vma || !(vma->vm_flags & VM_SHARED))

                goto out;

        if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))

                goto out;

        if (!(vma->vm_flags & VM_CAN_NONLINEAR))

                goto out;

        if (end <= start || start < vma->vm_start || end > vma->vm_end)

                goto out;

        /* Must set VM_NONLINEAR before any pages are populated. */

        if (!(vma->vm_flags & VM_NONLINEAR)) {

                /* Don't need a nonlinear mapping, exit success */

                if (pgoff == linear_page_index(vma, start)) {

                        err = 0;

                        goto out;

                }

                if (!has_write_lock) {

                        up_read(&mm->mmap_sem);

                        down_write(&mm->mmap_sem);

                        has_write_lock = 1;

                        goto retry;

                }

                mapping = vma->vm_file->f_mapping;

                /*

                 * page_mkclean doesn't work on nonlinear vmas, so if

                 * dirty pages need to be accounted, emulate with linear

                 * vmas.

                 */

                if (mapping_cap_account_dirty(mapping)) {

                        unsigned long addr;

                        flags &= MAP_NONBLOCK;

                        addr = mmap_region(vma->vm_file, start, size,

                                        flags, vma->vm_flags, pgoff, 1);

                        if (IS_ERR_VALUE(addr)) {

                                err = addr;

                        } else {

                                BUG_ON(addr != start);

                                err = 0;

                        }

                        goto out;

                }

                spin_lock(&mapping->i_mmap_lock);

                flush_dcache_mmap_lock(mapping);

                vma->vm_flags |= VM_NONLINEAR;

                vma_prio_tree_remove(vma, &mapping->i_mmap);

                vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);

                flush_dcache_mmap_unlock(mapping);

                spin_unlock(&mapping->i_mmap_lock);

        }

        err = populate_range(mm, vma, start, size, pgoff);

        if (!err && !(flags & MAP_NONBLOCK)) {

                if (unlikely(has_write_lock)) {

                        downgrade_write(&mm->mmap_sem);

                        has_write_lock = 0;

                }

                make_pages_present(start, start+size);

        }

        /*

         * We can't clear VM_NONLINEAR because we'd have to do

         * it after ->populate completes, and that would prevent

         * downgrading the lock.  (Locks can't be upgraded).

         */

out:

        if (likely(!has_write_lock))

                up_read(&mm->mmap_sem);

        else

                up_write(&mm->mmap_sem);

        return err;

}