/*
 *      mm/mremap.c
 *
 *      (C) Copyright 1996 Linus Torvalds
 *
 *      Address space accounting code   <alan@redhat.com>
 *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
 */

#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/slab.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/security.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pmd_t *pmd;
        pte_t *pte = NULL;

        pgd = pgd_offset(mm, addr);
        if (pgd_none(*pgd))
                goto end;
        if (pgd_bad(*pgd)) {
                pgd_ERROR(*pgd);
                pgd_clear(pgd);
                goto end;
        }

        pmd = pmd_offset(pgd, addr);
        if (pmd_none(*pmd))
                goto end;
        if (pmd_bad(*pmd)) {
                pmd_ERROR(*pmd);
                pmd_clear(pmd);
                goto end;
        }

        pte = pte_offset_map_nested(pmd, addr);
        if (pte_none(*pte)) {
                pte_unmap_nested(pte);
                pte = NULL;
        }
end:
        return pte;
}

static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pmd_t *pmd;

        pgd = pgd_offset(mm, addr);
        if (pgd_none(*pgd))
                return NULL;
        pmd = pmd_offset(pgd, addr);
        if (!pmd_present(*pmd))
                return NULL;
        return pte_offset_map(pmd, addr);
}

static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr)
{
        pmd_t *pmd;
        pte_t *pte = NULL;

        pmd = pmd_alloc(mm, pgd_offset(mm, addr), addr);
        if (pmd)
                pte = pte_alloc_map(mm, pmd, addr);
        return pte;
}

static int
move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
                unsigned long new_addr)
{
        struct address_space *mapping = NULL;
        struct mm_struct *mm = vma->vm_mm;
        int error = 0;
        pte_t *src, *dst;

        if (vma->vm_file) {
                /*
                 * Subtle point from Rajesh Venkatasubramanian: before
                 * moving file-based ptes, we must lock vmtruncate out,
                 * since it might clean the dst vma before the src vma,
                 * and we propagate stale pages into the dst afterward.
                 */
                mapping = vma->vm_file->f_mapping;
                spin_lock(&mapping->i_mmap_lock);
        }
        spin_lock(&mm->page_table_lock);

        src = get_one_pte_map_nested(mm, old_addr);
        if (src) {
                /*
                 * Look to see whether alloc_one_pte_map needs to perform a
                 * memory allocation.  If it does then we need to drop the
                 * atomic kmap
                 */
                dst = get_one_pte_map(mm, new_addr);
                if (unlikely(!dst)) {
                        pte_unmap_nested(src);
                        if (mapping)
                                spin_unlock(&mapping->i_mmap_lock);
                        dst = alloc_one_pte_map(mm, new_addr);
                        if (mapping && !spin_trylock(&mapping->i_mmap_lock)) {
                                spin_unlock(&mm->page_table_lock);
                                spin_lock(&mapping->i_mmap_lock);
                                spin_lock(&mm->page_table_lock);
                        }
                        src = get_one_pte_map_nested(mm, old_addr);
                }
                /*
                 * Since alloc_one_pte_map can drop and re-acquire
                 * page_table_lock, we should re-check the src entry...
                 */
                if (src) {
                        if (dst) {
                                pte_t pte;
                                pte = ptep_clear_flush(vma, old_addr, src);
                                set_pte(dst, pte);
                        } else
                                error = -ENOMEM;
                        pte_unmap_nested(src);
                }
                if (dst)
                        pte_unmap(dst);
        }
        spin_unlock(&mm->page_table_lock);
        if (mapping)
                spin_unlock(&mapping->i_mmap_lock);
        return error;
}

static unsigned long move_page_tables(struct vm_area_struct *vma,
                unsigned long new_addr, unsigned long old_addr,
                unsigned long len)
{
        unsigned long offset;

        flush_cache_range(vma, old_addr, old_addr + len);

        /*
         * This is not the clever way to do this, but we're taking the
         * easy way out on the assumption that most remappings will be
         * only a few pages.. This also makes error recovery easier.
         */
        for (offset = 0; offset < len; offset += PAGE_SIZE) {
                if (move_one_page(vma, old_addr+offset, new_addr+offset) < 0)
                        break;
                cond_resched();
        }
        return offset;
}

static unsigned long move_vma(struct vm_area_struct *vma,
                unsigned long old_addr, unsigned long old_len,
                unsigned long new_len, unsigned long new_addr)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma;
        unsigned long vm_flags = vma->vm_flags;
        unsigned long new_pgoff;
        unsigned long moved_len;
        unsigned long excess = 0;
        int split = 0;

        /*
         * We'd prefer to avoid failure later on in do_munmap:
         * which may split one vma into three before unmapping.
         */
        if (mm->map_count >= sysctl_max_map_count - 3)
                return -ENOMEM;

        new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
        new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);
        if (!new_vma)
                return -ENOMEM;

        moved_len = move_page_tables(vma, new_addr, old_addr, old_len);
        if (moved_len < old_len) {
                /*
                 * On error, move entries back from new area to old,
                 * which will succeed since page tables still there,
                 * and then proceed to unmap new area instead of old.
                 */
                move_page_tables(new_vma, old_addr, new_addr, moved_len);
                vma = new_vma;
                old_len = new_len;
                old_addr = new_addr;
                new_addr = -ENOMEM;
        }

        /* Conceal VM_ACCOUNT so old reservation is not undone */
        if (vm_flags & VM_ACCOUNT) {
                vma->vm_flags &= ~VM_ACCOUNT;
                excess = vma->vm_end - vma->vm_start - old_len;
                if (old_addr > vma->vm_start &&
                    old_addr + old_len < vma->vm_end)
                        split = 1;
        }

        if (do_munmap(mm, old_addr, old_len) < 0) {
                /* OOM: unable to split vma, just get accounts right */
                vm_unacct_memory(excess >> PAGE_SHIFT);
                excess = 0;
        }

        /* Restore VM_ACCOUNT if one or two pieces of vma left */
        if (excess) {
                vma->vm_flags |= VM_ACCOUNT;
                if (split)
                        vma->vm_next->vm_flags |= VM_ACCOUNT;
        }

        mm->total_vm += new_len >> PAGE_SHIFT;
        __vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                mm->locked_vm += new_len >> PAGE_SHIFT;
                if (new_len > old_len)
                        make_pages_present(new_addr + old_len,
                                           new_addr + new_len);
        }

        return new_addr;
}

/*
 * Expand (or shrink) an existing mapping, potentially moving it at the
 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 * This option implies MREMAP_MAYMOVE.
 */
unsigned long do_mremap(unsigned long addr,
        unsigned long old_len, unsigned long new_len,
        unsigned long flags, unsigned long new_addr)
{
        struct vm_area_struct *vma;
        unsigned long ret = -EINVAL;
        unsigned long charged = 0;

        if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
                goto out;

        if (addr & ~PAGE_MASK)
                goto out;

        old_len = PAGE_ALIGN(old_len);
        new_len = PAGE_ALIGN(new_len);

        /*
         * We allow a zero old-len as a special case
         * for DOS-emu "duplicate shm area" thing. But
         * a zero new-len is nonsensical.
         */
        if (!new_len)
                goto out;

        /* new_addr is only valid if MREMAP_FIXED is specified */
        if (flags & MREMAP_FIXED) {
                if (new_addr & ~PAGE_MASK)
                        goto out;
                if (!(flags & MREMAP_MAYMOVE))
                        goto out;

                if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
                        goto out;

                /* Check if the location we're moving into overlaps the
                 * old location at all, and fail if it does.
                 */
                if ((new_addr <= addr) && (new_addr+new_len) > addr)
                        goto out;

                if ((addr <= new_addr) && (addr+old_len) > new_addr)
                        goto out;

                ret = do_munmap(current->mm, new_addr, new_len);
                if (ret)
                        goto out;
        }

        /*
         * Always allow a shrinking remap: that just unmaps
         * the unnecessary pages..
         * do_munmap does all the needed commit accounting
         */
        if (old_len >= new_len) {
                ret = do_munmap(current->mm, addr+new_len, old_len - new_len);
                if (ret && old_len != new_len)
                        goto out;
                ret = addr;
                if (!(flags & MREMAP_FIXED) || (new_addr == addr))
                        goto out;
                old_len = new_len;
        }

        /*
         * Ok, we need to grow..  or relocate.
         */
        ret = -EFAULT;
        vma = find_vma(current->mm, addr);
        if (!vma || vma->vm_start > addr)
                goto out;
        if (is_vm_hugetlb_page(vma)) {
                ret = -EINVAL;
                goto out;
        }
        /* We can't remap across vm area boundaries */
        if (old_len > vma->vm_end - addr)
                goto out;
        if (vma->vm_flags & VM_DONTEXPAND) {
                if (new_len > old_len)
                        goto out;
        }
        if (vma->vm_flags & VM_LOCKED) {
                unsigned long locked, lock_limit;
                locked = current->mm->locked_vm << PAGE_SHIFT;
                lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
                locked += new_len - old_len;
                ret = -EAGAIN;
                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                        goto out;
        }
        ret = -ENOMEM;
        if ((current->mm->total_vm << PAGE_SHIFT) + (new_len - old_len)
            > current->rlim[RLIMIT_AS].rlim_cur)
                goto out;

        if (vma->vm_flags & VM_ACCOUNT) {
                charged = (new_len - old_len) >> PAGE_SHIFT;
                if (security_vm_enough_memory(charged))
                        goto out_nc;
        }

        /* old_len exactly to the end of the area..
         * And we're not relocating the area.
         */
        if (old_len == vma->vm_end - addr &&
            !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
            (old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
                unsigned long max_addr = TASK_SIZE;
                if (vma->vm_next)
                        max_addr = vma->vm_next->vm_start;
                /* can we just expand the current mapping? */
                if (max_addr - addr >= new_len) {
                        int pages = (new_len - old_len) >> PAGE_SHIFT;

                        vma_adjust(vma, vma->vm_start,
                                addr + new_len, vma->vm_pgoff, NULL);

                        current->mm->total_vm += pages;
                        __vm_stat_account(vma->vm_mm, vma->vm_flags,
                                                        vma->vm_file, pages);
                        if (vma->vm_flags & VM_LOCKED) {
                                current->mm->locked_vm += pages;
                                make_pages_present(addr + old_len,
                                                   addr + new_len);
                        }
                        ret = addr;
                        goto out;
                }
        }

        /*
         * We weren't able to just expand or shrink the area,
         * we need to create a new one and move it..
         */
        ret = -ENOMEM;
        if (flags & MREMAP_MAYMOVE) {
                if (!(flags & MREMAP_FIXED)) {
                        unsigned long map_flags = 0;
                        if (vma->vm_flags & VM_MAYSHARE)
                                map_flags |= MAP_SHARED;

                        new_addr = get_unmapped_area_prot(vma->vm_file, 0, new_len, 
                                vma->vm_pgoff, map_flags, vma->vm_flags & VM_EXEC);
                        ret = new_addr;
                        if (new_addr & ~PAGE_MASK)
                                goto out;
                }
                ret = move_vma(vma, addr, old_len, new_len, new_addr);
        }
out:
        if (ret & ~PAGE_MASK)
                vm_unacct_memory(charged);
out_nc:
        return ret;
}

asmlinkage unsigned long sys_mremap(unsigned long addr,
        unsigned long old_len, unsigned long new_len,
        unsigned long flags, unsigned long new_addr)
{
        unsigned long ret;

        down_write(&current->mm->mmap_sem);
        ret = do_mremap(addr, old_len, new_len, flags, new_addr);
        up_write(&current->mm->mmap_sem);
        return ret;
}