nommu.c

Go to the documentation of this file.

/*
 *  linux/mm/nommu.c
 *
 *  Replacement code for mm functions to support CPU's that don't
 *  have any form of memory management unit (thus no virtual memory).
 *
 *  See Documentation/nommu-mmap.txt
 *
 *  Copyright (c) 2004-2008 David Howells <[email protected]>
 *  Copyright (c) 2000-2003 David McCullough <[email protected]>
 *  Copyright (c) 2000-2001 D Jeff Dionne <[email protected]>
 *  Copyright (c) 2002      Greg Ungerer <[email protected]>
 *  Copyright (c) 2007-2010 Paul Mundt <[email protected]>
 */

#include <linux/export.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/mount.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>

#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include "internal.h"

#if 0
#define kenter(FMT, ...) \
    printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
#define kleave(FMT, ...) \
    printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
#define kdebug(FMT, ...) \
    printk(KERN_DEBUG "xxx" FMT"yyy\n", ##__VA_ARGS__)
#else
#define kenter(FMT, ...) \
    no_printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
#define kleave(FMT, ...) \
    no_printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
#define kdebug(FMT, ...) \
    no_printk(KERN_DEBUG FMT"\n", ##__VA_ARGS__)
#endif

void *high_memory;
struct page *mem_map;
unsigned long max_mapnr;
unsigned long num_physpages;
unsigned long highest_memmap_pfn;
struct percpu_counter vm_committed_as;
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
int heap_stack_gap = 0;

atomic_long_t mmap_pages_allocated;

EXPORT_SYMBOL(mem_map);
EXPORT_SYMBOL(num_physpages);

/* list of mapped, potentially shareable regions */
static struct kmem_cache *vm_region_jar;
struct rb_root nommu_region_tree = RB_ROOT;
DECLARE_RWSEM(nommu_region_sem);

const struct vm_operations_struct generic_file_vm_ops = {
};

/*
 * Return the total memory allocated for this pointer, not
 * just what the caller asked for.
 *
 * Doesn't have to be accurate, i.e. may have races.
 */
unsigned int kobjsize(const void *objp)
{
    struct page *page;

    /*
     * If the object we have should not have ksize performed on it,
     * return size of 0
     */
    if (!objp || !virt_addr_valid(objp))
        return 0;

    page = virt_to_head_page(objp);

    /*
     * If the allocator sets PageSlab, we know the pointer came from
     * kmalloc().
     */
    if (PageSlab(page))
        return ksize(objp);

    /*
     * If it's not a compound page, see if we have a matching VMA
     * region. This test is intentionally done in reverse order,
     * so if there's no VMA, we still fall through and hand back
     * PAGE_SIZE for 0-order pages.
     */
    if (!PageCompound(page)) {
        struct vm_area_struct *vma;

        vma = find_vma(current->mm, (unsigned long)objp);
        if (vma)
            return vma->vm_end - vma->vm_start;
    }

    /*
     * The ksize() function is only guaranteed to work for pointers
     * returned by kmalloc(). So handle arbitrary pointers here.
     */
    return PAGE_SIZE << compound_order(page);
}

int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
             unsigned long start, int nr_pages, unsigned int foll_flags,
             struct page **pages, struct vm_area_struct **vmas,
             int *retry)
{
    struct vm_area_struct *vma;
    unsigned long vm_flags;
    int i;

    /* calculate required read or write permissions.
     * If FOLL_FORCE is set, we only require the "MAY" flags.
     */
    vm_flags  = (foll_flags & FOLL_WRITE) ?
            (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
    vm_flags &= (foll_flags & FOLL_FORCE) ?
            (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

    for (i = 0; i < nr_pages; i++) {
        vma = find_vma(mm, start);
        if (!vma)
            goto finish_or_fault;

        /* protect what we can, including chardevs */
        if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
            !(vm_flags & vma->vm_flags))
            goto finish_or_fault;

        if (pages) {
            pages[i] = virt_to_page(start);
            if (pages[i])
                page_cache_get(pages[i]);
        }
        if (vmas)
            vmas[i] = vma;
        start = (start + PAGE_SIZE) & PAGE_MASK;
    }

    return i;

finish_or_fault:
    return i ? : -EFAULT;
}

/*
 * get a list of pages in an address range belonging to the specified process
 * and indicate the VMA that covers each page
 * - this is potentially dodgy as we may end incrementing the page count of a
 *   slab page or a secondary page from a compound page
 * - don't permit access to VMAs that don't support it, such as I/O mappings
 */
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
    unsigned long start, int nr_pages, int write, int force,
    struct page **pages, struct vm_area_struct **vmas)
{
    int flags = 0;

    if (write)
        flags |= FOLL_WRITE;
    if (force)
        flags |= FOLL_FORCE;

    return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
                NULL);
}
EXPORT_SYMBOL(get_user_pages);

int follow_pfn(struct vm_area_struct *vma, unsigned long address,
    unsigned long *pfn)
{
    if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
        return -EINVAL;

    *pfn = address >> PAGE_SHIFT;
    return 0;
}
EXPORT_SYMBOL(follow_pfn);

DEFINE_RWLOCK(vmlist_lock);
struct vm_struct *vmlist;

void vfree(const void *addr)
{
    kfree(addr);
}
EXPORT_SYMBOL(vfree);

void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
{
    /*
     *  You can't specify __GFP_HIGHMEM with kmalloc() since kmalloc()
     * returns only a logical address.
     */
    return kmalloc(size, (gfp_mask | __GFP_COMP) & ~__GFP_HIGHMEM);
}
EXPORT_SYMBOL(__vmalloc);

void *vmalloc_user(unsigned long size)
{
    void *ret;

    ret = __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
            PAGE_KERNEL);
    if (ret) {
        struct vm_area_struct *vma;

        down_write(&current->mm->mmap_sem);
        vma = find_vma(current->mm, (unsigned long)ret);
        if (vma)
            vma->vm_flags |= VM_USERMAP;
        up_write(&current->mm->mmap_sem);
    }

    return ret;
}
EXPORT_SYMBOL(vmalloc_user);

struct page *vmalloc_to_page(const void *addr)
{
    return virt_to_page(addr);
}
EXPORT_SYMBOL(vmalloc_to_page);

unsigned long vmalloc_to_pfn(const void *addr)
{
    return page_to_pfn(virt_to_page(addr));
}
EXPORT_SYMBOL(vmalloc_to_pfn);

long vread(char *buf, char *addr, unsigned long count)
{
    memcpy(buf, addr, count);
    return count;
}

long vwrite(char *buf, char *addr, unsigned long count)
{
    /* Don't allow overflow */
    if ((unsigned long) addr + count < count)
        count = -(unsigned long) addr;

    memcpy(addr, buf, count);
    return(count);
}

/*
 *  vmalloc  -  allocate virtually continguos memory
 *
 *  @size:      allocation size
 *
 *  Allocate enough pages to cover @size from the page level
 *  allocator and map them into continguos kernel virtual space.
 *
 *  For tight control over page level allocator and protection flags
 *  use __vmalloc() instead.
 */
void *vmalloc(unsigned long size)
{
       return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc);

/*
 *  vzalloc - allocate virtually continguos memory with zero fill
 *
 *  @size:      allocation size
 *
 *  Allocate enough pages to cover @size from the page level
 *  allocator and map them into continguos kernel virtual space.
 *  The memory allocated is set to zero.
 *
 *  For tight control over page level allocator and protection flags
 *  use __vmalloc() instead.
 */
void *vzalloc(unsigned long size)
{
    return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
            PAGE_KERNEL);
}
EXPORT_SYMBOL(vzalloc);

void *vmalloc_node(unsigned long size, int node)
{
    return vmalloc(size);
}
EXPORT_SYMBOL(vmalloc_node);

void *vzalloc_node(unsigned long size, int node)
{
    return vzalloc(size);
}
EXPORT_SYMBOL(vzalloc_node);

#ifndef PAGE_KERNEL_EXEC
# define PAGE_KERNEL_EXEC PAGE_KERNEL
#endif

void *vmalloc_exec(unsigned long size)
{
    return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC);
}

void *vmalloc_32(unsigned long size)
{
    return __vmalloc(size, GFP_KERNEL, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc_32);

void *vmalloc_32_user(unsigned long size)
{
    /*
     * We'll have to sort out the ZONE_DMA bits for 64-bit,
     * but for now this can simply use vmalloc_user() directly.
     */
    return vmalloc_user(size);
}
EXPORT_SYMBOL(vmalloc_32_user);

void *vmap(struct page **pages, unsigned int count, unsigned long flags, pgprot_t prot)
{
    BUG();
    return NULL;
}
EXPORT_SYMBOL(vmap);

void vunmap(const void *addr)
{
    BUG();
}
EXPORT_SYMBOL(vunmap);

void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t prot)
{
    BUG();
    return NULL;
}
EXPORT_SYMBOL(vm_map_ram);

void vm_unmap_ram(const void *mem, unsigned int count)
{
    BUG();
}
EXPORT_SYMBOL(vm_unmap_ram);

void vm_unmap_aliases(void)
{
}
EXPORT_SYMBOL_GPL(vm_unmap_aliases);

/*
 * Implement a stub for vmalloc_sync_all() if the architecture chose not to
 * have one.
 */
void  __attribute__((weak)) vmalloc_sync_all(void)
{
}

struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes)
{
    BUG();
    return NULL;
}
EXPORT_SYMBOL_GPL(alloc_vm_area);

void free_vm_area(struct vm_struct *area)
{
    BUG();
}
EXPORT_SYMBOL_GPL(free_vm_area);

int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
           struct page *page)
{
    return -EINVAL;
}
EXPORT_SYMBOL(vm_insert_page);

/*
 *  sys_brk() for the most part doesn't need the global kernel
 *  lock, except when an application is doing something nasty
 *  like trying to un-brk an area that has already been mapped
 *  to a regular file.  in this case, the unmapping will need
 *  to invoke file system routines that need the global lock.
 */
SYSCALL_DEFINE1(brk, unsigned long, brk)
{
    struct mm_struct *mm = current->mm;

    if (brk < mm->start_brk || brk > mm->context.end_brk)
        return mm->brk;

    if (mm->brk == brk)
        return mm->brk;

    /*
     * Always allow shrinking brk
     */
    if (brk <= mm->brk) {
        mm->brk = brk;
        return brk;
    }

    /*
     * Ok, looks good - let it rip.
     */
    flush_icache_range(mm->brk, brk);
    return mm->brk = brk;
}

/*
 * initialise the VMA and region record slabs
 */
void __init mmap_init(void)
{
    int ret;

    ret = percpu_counter_init(&vm_committed_as, 0);
    VM_BUG_ON(ret);
    vm_region_jar = KMEM_CACHE(vm_region, SLAB_PANIC);
}

/*
 * validate the region tree
 * - the caller must hold the region lock
 */
#ifdef CONFIG_DEBUG_NOMMU_REGIONS
static noinline void validate_nommu_regions(void)
{
    struct vm_region *region, *last;
    struct rb_node *p, *lastp;

    lastp = rb_first(&nommu_region_tree);
    if (!lastp)
        return;

    last = rb_entry(lastp, struct vm_region, vm_rb);
    BUG_ON(unlikely(last->vm_end <= last->vm_start));
    BUG_ON(unlikely(last->vm_top < last->vm_end));

    while ((p = rb_next(lastp))) {
        region = rb_entry(p, struct vm_region, vm_rb);
        last = rb_entry(lastp, struct vm_region, vm_rb);

        BUG_ON(unlikely(region->vm_end <= region->vm_start));
        BUG_ON(unlikely(region->vm_top < region->vm_end));
        BUG_ON(unlikely(region->vm_start < last->vm_top));

        lastp = p;
    }
}
#else
static void validate_nommu_regions(void)
{
}
#endif

/*
 * add a region into the global tree
 */
static void add_nommu_region(struct vm_region *region)
{
    struct vm_region *pregion;
    struct rb_node **p, *parent;

    validate_nommu_regions();

    parent = NULL;
    p = &nommu_region_tree.rb_node;
    while (*p) {
        parent = *p;
        pregion = rb_entry(parent, struct vm_region, vm_rb);
        if (region->vm_start < pregion->vm_start)
            p = &(*p)->rb_left;
        else if (region->vm_start > pregion->vm_start)
            p = &(*p)->rb_right;
        else if (pregion == region)
            return;
        else
            BUG();
    }

    rb_link_node(&region->vm_rb, parent, p);
    rb_insert_color(&region->vm_rb, &nommu_region_tree);

    validate_nommu_regions();
}

/*
 * delete a region from the global tree
 */
static void delete_nommu_region(struct vm_region *region)
{
    BUG_ON(!nommu_region_tree.rb_node);

    validate_nommu_regions();
    rb_erase(&region->vm_rb, &nommu_region_tree);
    validate_nommu_regions();
}

/*
 * free a contiguous series of pages
 */
static void free_page_series(unsigned long from, unsigned long to)
{
    for (; from < to; from += PAGE_SIZE) {
        struct page *page = virt_to_page(from);

        kdebug("- free %lx", from);
        atomic_long_dec(&mmap_pages_allocated);
        if (page_count(page) != 1)
            kdebug("free page %p: refcount not one: %d",
                   page, page_count(page));
        put_page(page);
    }
}

/*
 * release a reference to a region
 * - the caller must hold the region semaphore for writing, which this releases
 * - the region may not have been added to the tree yet, in which case vm_top
 *   will equal vm_start
 */
static void __put_nommu_region(struct vm_region *region)
    __releases(nommu_region_sem)
{
    kenter("%p{%d}", region, region->vm_usage);

    BUG_ON(!nommu_region_tree.rb_node);

    if (--region->vm_usage == 0) {
        if (region->vm_top > region->vm_start)
            delete_nommu_region(region);
        up_write(&nommu_region_sem);

        if (region->vm_file)
            fput(region->vm_file);

        /* IO memory and memory shared directly out of the pagecache
         * from ramfs/tmpfs mustn't be released here */
        if (region->vm_flags & VM_MAPPED_COPY) {
            kdebug("free series");
            free_page_series(region->vm_start, region->vm_top);
        }
        kmem_cache_free(vm_region_jar, region);
    } else {
        up_write(&nommu_region_sem);
    }
}

/*
 * release a reference to a region
 */
static void put_nommu_region(struct vm_region *region)
{
    down_write(&nommu_region_sem);
    __put_nommu_region(region);
}

/*
 * update protection on a vma
 */
static void protect_vma(struct vm_area_struct *vma, unsigned long flags)
{
#ifdef CONFIG_MPU
    struct mm_struct *mm = vma->vm_mm;
    long start = vma->vm_start & PAGE_MASK;
    while (start < vma->vm_end) {
        protect_page(mm, start, flags);
        start += PAGE_SIZE;
    }
    update_protections(mm);
#endif
}

/*
 * add a VMA into a process's mm_struct in the appropriate place in the list
 * and tree and add to the address space's page tree also if not an anonymous
 * page
 * - should be called with mm->mmap_sem held writelocked
 */
static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
{
    struct vm_area_struct *pvma, *prev;
    struct address_space *mapping;
    struct rb_node **p, *parent, *rb_prev;

    kenter(",%p", vma);

    BUG_ON(!vma->vm_region);

    mm->map_count++;
    vma->vm_mm = mm;

    protect_vma(vma, vma->vm_flags);

    /* add the VMA to the mapping */
    if (vma->vm_file) {
        mapping = vma->vm_file->f_mapping;

        mutex_lock(&mapping->i_mmap_mutex);
        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_insert(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
        mutex_unlock(&mapping->i_mmap_mutex);
    }

    /* add the VMA to the tree */
    parent = rb_prev = NULL;
    p = &mm->mm_rb.rb_node;
    while (*p) {
        parent = *p;
        pvma = rb_entry(parent, struct vm_area_struct, vm_rb);

        /* sort by: start addr, end addr, VMA struct addr in that order
         * (the latter is necessary as we may get identical VMAs) */
        if (vma->vm_start < pvma->vm_start)
            p = &(*p)->rb_left;
        else if (vma->vm_start > pvma->vm_start) {
            rb_prev = parent;
            p = &(*p)->rb_right;
        } else if (vma->vm_end < pvma->vm_end)
            p = &(*p)->rb_left;
        else if (vma->vm_end > pvma->vm_end) {
            rb_prev = parent;
            p = &(*p)->rb_right;
        } else if (vma < pvma)
            p = &(*p)->rb_left;
        else if (vma > pvma) {
            rb_prev = parent;
            p = &(*p)->rb_right;
        } else
            BUG();
    }

    rb_link_node(&vma->vm_rb, parent, p);
    rb_insert_color(&vma->vm_rb, &mm->mm_rb);

    /* add VMA to the VMA list also */
    prev = NULL;
    if (rb_prev)
        prev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);

    __vma_link_list(mm, vma, prev, parent);
}

/*
 * delete a VMA from its owning mm_struct and address space
 */
static void delete_vma_from_mm(struct vm_area_struct *vma)
{
    struct address_space *mapping;
    struct mm_struct *mm = vma->vm_mm;

    kenter("%p", vma);

    protect_vma(vma, 0);

    mm->map_count--;
    if (mm->mmap_cache == vma)
        mm->mmap_cache = NULL;

    /* remove the VMA from the mapping */
    if (vma->vm_file) {
        mapping = vma->vm_file->f_mapping;

        mutex_lock(&mapping->i_mmap_mutex);
        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_remove(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
        mutex_unlock(&mapping->i_mmap_mutex);
    }

    /* remove from the MM's tree and list */
    rb_erase(&vma->vm_rb, &mm->mm_rb);

    if (vma->vm_prev)
        vma->vm_prev->vm_next = vma->vm_next;
    else
        mm->mmap = vma->vm_next;

    if (vma->vm_next)
        vma->vm_next->vm_prev = vma->vm_prev;
}

/*
 * destroy a VMA record
 */
static void delete_vma(struct mm_struct *mm, struct vm_area_struct *vma)
{
    kenter("%p", vma);
    if (vma->vm_ops && vma->vm_ops->close)
        vma->vm_ops->close(vma);
    if (vma->vm_file)
        fput(vma->vm_file);
    put_nommu_region(vma->vm_region);
    kmem_cache_free(vm_area_cachep, vma);
}

/*
 * look up the first VMA in which addr resides, NULL if none
 * - should be called with mm->mmap_sem at least held readlocked
 */
struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
{
    struct vm_area_struct *vma;

    /* check the cache first */
    vma = mm->mmap_cache;
    if (vma && vma->vm_start <= addr && vma->vm_end > addr)
        return vma;

    /* trawl the list (there may be multiple mappings in which addr
     * resides) */
    for (vma = mm->mmap; vma; vma = vma->vm_next) {
        if (vma->vm_start > addr)
            return NULL;
        if (vma->vm_end > addr) {
            mm->mmap_cache = vma;
            return vma;
        }
    }

    return NULL;
}
EXPORT_SYMBOL(find_vma);

/*
 * find a VMA
 * - we don't extend stack VMAs under NOMMU conditions
 */
struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
    return find_vma(mm, addr);
}

/*
 * expand a stack to a given address
 * - not supported under NOMMU conditions
 */
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
    return -ENOMEM;
}

/*
 * look up the first VMA exactly that exactly matches addr
 * - should be called with mm->mmap_sem at least held readlocked
 */
static struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
                         unsigned long addr,
                         unsigned long len)
{
    struct vm_area_struct *vma;
    unsigned long end = addr + len;

    /* check the cache first */
    vma = mm->mmap_cache;
    if (vma && vma->vm_start == addr && vma->vm_end == end)
        return vma;

    /* trawl the list (there may be multiple mappings in which addr
     * resides) */
    for (vma = mm->mmap; vma; vma = vma->vm_next) {
        if (vma->vm_start < addr)
            continue;
        if (vma->vm_start > addr)
            return NULL;
        if (vma->vm_end == end) {
            mm->mmap_cache = vma;
            return vma;
        }
    }

    return NULL;
}

/*
 * determine whether a mapping should be permitted and, if so, what sort of
 * mapping we're capable of supporting
 */
static int validate_mmap_request(struct file *file,
                 unsigned long addr,
                 unsigned long len,
                 unsigned long prot,
                 unsigned long flags,
                 unsigned long pgoff,
                 unsigned long *_capabilities)
{
    unsigned long capabilities, rlen;
    int ret;

    /* do the simple checks first */
    if (flags & MAP_FIXED) {
        printk(KERN_DEBUG
               "%d: Can't do fixed-address/overlay mmap of RAM\n",
               current->pid);
        return -EINVAL;
    }

    if ((flags & MAP_TYPE) != MAP_PRIVATE &&
        (flags & MAP_TYPE) != MAP_SHARED)
        return -EINVAL;

    if (!len)
        return -EINVAL;

    /* Careful about overflows.. */
    rlen = PAGE_ALIGN(len);
    if (!rlen || rlen > TASK_SIZE)
        return -ENOMEM;

    /* offset overflow? */
    if ((pgoff + (rlen >> PAGE_SHIFT)) < pgoff)
        return -EOVERFLOW;

    if (file) {
        /* validate file mapping requests */
        struct address_space *mapping;

        /* files must support mmap */
        if (!file->f_op || !file->f_op->mmap)
            return -ENODEV;

        /* work out if what we've got could possibly be shared
         * - we support chardevs that provide their own "memory"
         * - we support files/blockdevs that are memory backed
         */
        mapping = file->f_mapping;
        if (!mapping)
            mapping = file->f_path.dentry->d_inode->i_mapping;

        capabilities = 0;
        if (mapping && mapping->backing_dev_info)
            capabilities = mapping->backing_dev_info->capabilities;

        if (!capabilities) {
            /* no explicit capabilities set, so assume some
             * defaults */
            switch (file->f_path.dentry->d_inode->i_mode & S_IFMT) {
            case S_IFREG:
            case S_IFBLK:
                capabilities = BDI_CAP_MAP_COPY;
                break;

            case S_IFCHR:
                capabilities =
                    BDI_CAP_MAP_DIRECT |
                    BDI_CAP_READ_MAP |
                    BDI_CAP_WRITE_MAP;
                break;

            default:
                return -EINVAL;
            }
        }

        /* eliminate any capabilities that we can't support on this
         * device */
        if (!file->f_op->get_unmapped_area)
            capabilities &= ~BDI_CAP_MAP_DIRECT;
        if (!file->f_op->read)
            capabilities &= ~BDI_CAP_MAP_COPY;

        /* The file shall have been opened with read permission. */
        if (!(file->f_mode & FMODE_READ))
            return -EACCES;

        if (flags & MAP_SHARED) {
            /* do checks for writing, appending and locking */
            if ((prot & PROT_WRITE) &&
                !(file->f_mode & FMODE_WRITE))
                return -EACCES;

            if (IS_APPEND(file->f_path.dentry->d_inode) &&
                (file->f_mode & FMODE_WRITE))
                return -EACCES;

            if (locks_verify_locked(file->f_path.dentry->d_inode))
                return -EAGAIN;

            if (!(capabilities & BDI_CAP_MAP_DIRECT))
                return -ENODEV;

            /* we mustn't privatise shared mappings */
            capabilities &= ~BDI_CAP_MAP_COPY;
        }
        else {
            /* we're going to read the file into private memory we
             * allocate */
            if (!(capabilities & BDI_CAP_MAP_COPY))
                return -ENODEV;

            /* we don't permit a private writable mapping to be
             * shared with the backing device */
            if (prot & PROT_WRITE)
                capabilities &= ~BDI_CAP_MAP_DIRECT;
        }

        if (capabilities & BDI_CAP_MAP_DIRECT) {
            if (((prot & PROT_READ)  && !(capabilities & BDI_CAP_READ_MAP))  ||
                ((prot & PROT_WRITE) && !(capabilities & BDI_CAP_WRITE_MAP)) ||
                ((prot & PROT_EXEC)  && !(capabilities & BDI_CAP_EXEC_MAP))
                ) {
                capabilities &= ~BDI_CAP_MAP_DIRECT;
                if (flags & MAP_SHARED) {
                    printk(KERN_WARNING
                           "MAP_SHARED not completely supported on !MMU\n");
                    return -EINVAL;
                }
            }
        }

        /* handle executable mappings and implied executable
         * mappings */
        if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
            if (prot & PROT_EXEC)
                return -EPERM;
        }
        else if ((prot & PROT_READ) && !(prot & PROT_EXEC)) {
            /* handle implication of PROT_EXEC by PROT_READ */
            if (current->personality & READ_IMPLIES_EXEC) {
                if (capabilities & BDI_CAP_EXEC_MAP)
                    prot |= PROT_EXEC;
            }
        }
        else if ((prot & PROT_READ) &&
             (prot & PROT_EXEC) &&
             !(capabilities & BDI_CAP_EXEC_MAP)
             ) {
            /* backing file is not executable, try to copy */
            capabilities &= ~BDI_CAP_MAP_DIRECT;
        }
    }
    else {
        /* anonymous mappings are always memory backed and can be
         * privately mapped
         */
        capabilities = BDI_CAP_MAP_COPY;

        /* handle PROT_EXEC implication by PROT_READ */
        if ((prot & PROT_READ) &&
            (current->personality & READ_IMPLIES_EXEC))
            prot |= PROT_EXEC;
    }

    /* allow the security API to have its say */
    ret = security_mmap_addr(addr);
    if (ret < 0)
        return ret;

    /* looks okay */
    *_capabilities = capabilities;
    return 0;
}

/*
 * we've determined that we can make the mapping, now translate what we
 * now know into VMA flags
 */
static unsigned long determine_vm_flags(struct file *file,
                    unsigned long prot,
                    unsigned long flags,
                    unsigned long capabilities)
{
    unsigned long vm_flags;

    vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags);
    /* vm_flags |= mm->def_flags; */

    if (!(capabilities & BDI_CAP_MAP_DIRECT)) {
        /* attempt to share read-only copies of mapped file chunks */
        vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
        if (file && !(prot & PROT_WRITE))
            vm_flags |= VM_MAYSHARE;
    } else {
        /* overlay a shareable mapping on the backing device or inode
         * if possible - used for chardevs, ramfs/tmpfs/shmfs and
         * romfs/cramfs */
        vm_flags |= VM_MAYSHARE | (capabilities & BDI_CAP_VMFLAGS);
        if (flags & MAP_SHARED)
            vm_flags |= VM_SHARED;
    }

    /* refuse to let anyone share private mappings with this process if
     * it's being traced - otherwise breakpoints set in it may interfere
     * with another untraced process
     */
    if ((flags & MAP_PRIVATE) && current->ptrace)
        vm_flags &= ~VM_MAYSHARE;

    return vm_flags;
}

/*
 * set up a shared mapping on a file (the driver or filesystem provides and
 * pins the storage)
 */
static int do_mmap_shared_file(struct vm_area_struct *vma)
{
    int ret;

    ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
    if (ret == 0) {
        vma->vm_region->vm_top = vma->vm_region->vm_end;
        return 0;
    }
    if (ret != -ENOSYS)
        return ret;

    /* getting -ENOSYS indicates that direct mmap isn't possible (as
     * opposed to tried but failed) so we can only give a suitable error as
     * it's not possible to make a private copy if MAP_SHARED was given */
    return -ENODEV;
}

/*
 * set up a private mapping or an anonymous shared mapping
 */
static int do_mmap_private(struct vm_area_struct *vma,
               struct vm_region *region,
               unsigned long len,
               unsigned long capabilities)
{
    struct page *pages;
    unsigned long total, point, n;
    void *base;
    int ret, order;

    /* invoke the file's mapping function so that it can keep track of
     * shared mappings on devices or memory
     * - VM_MAYSHARE will be set if it may attempt to share
     */
    if (capabilities & BDI_CAP_MAP_DIRECT) {
        ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
        if (ret == 0) {
            /* shouldn't return success if we're not sharing */
            BUG_ON(!(vma->vm_flags & VM_MAYSHARE));
            vma->vm_region->vm_top = vma->vm_region->vm_end;
            return 0;
        }
        if (ret != -ENOSYS)
            return ret;

        /* getting an ENOSYS error indicates that direct mmap isn't
         * possible (as opposed to tried but failed) so we'll try to
         * make a private copy of the data and map that instead */
    }


    /* allocate some memory to hold the mapping
     * - note that this may not return a page-aligned address if the object
     *   we're allocating is smaller than a page
     */
    order = get_order(len);
    kdebug("alloc order %d for %lx", order, len);

    pages = alloc_pages(GFP_KERNEL, order);
    if (!pages)
        goto enomem;

    total = 1 << order;
    atomic_long_add(total, &mmap_pages_allocated);

    point = len >> PAGE_SHIFT;

    /* we allocated a power-of-2 sized page set, so we may want to trim off
     * the excess */
    if (sysctl_nr_trim_pages && total - point >= sysctl_nr_trim_pages) {
        while (total > point) {
            order = ilog2(total - point);
            n = 1 << order;
            kdebug("shave %lu/%lu @%lu", n, total - point, total);
            atomic_long_sub(n, &mmap_pages_allocated);
            total -= n;
            set_page_refcounted(pages + total);
            __free_pages(pages + total, order);
        }
    }

    for (point = 1; point < total; point++)
        set_page_refcounted(&pages[point]);

    base = page_address(pages);
    region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
    region->vm_start = (unsigned long) base;
    region->vm_end   = region->vm_start + len;
    region->vm_top   = region->vm_start + (total << PAGE_SHIFT);

    vma->vm_start = region->vm_start;
    vma->vm_end   = region->vm_start + len;

    if (vma->vm_file) {
        /* read the contents of a file into the copy */
        mm_segment_t old_fs;
        loff_t fpos;

        fpos = vma->vm_pgoff;
        fpos <<= PAGE_SHIFT;

        old_fs = get_fs();
        set_fs(KERNEL_DS);
        ret = vma->vm_file->f_op->read(vma->vm_file, base, len, &fpos);
        set_fs(old_fs);

        if (ret < 0)
            goto error_free;

        /* clear the last little bit */
        if (ret < len)
            memset(base + ret, 0, len - ret);

    }

    return 0;

error_free:
    free_page_series(region->vm_start, region->vm_top);
    region->vm_start = vma->vm_start = 0;
    region->vm_end   = vma->vm_end = 0;
    region->vm_top   = 0;
    return ret;

enomem:
    printk("Allocation of length %lu from process %d (%s) failed\n",
           len, current->pid, current->comm);
    show_free_areas(0);
    return -ENOMEM;
}

/*
 * handle mapping creation for uClinux
 */
unsigned long do_mmap_pgoff(struct file *file,
                unsigned long addr,
                unsigned long len,
                unsigned long prot,
                unsigned long flags,
                unsigned long pgoff)
{
    struct vm_area_struct *vma;
    struct vm_region *region;
    struct rb_node *rb;
    unsigned long capabilities, vm_flags, result;
    int ret;

    kenter(",%lx,%lx,%lx,%lx,%lx", addr, len, prot, flags, pgoff);

    /* decide whether we should attempt the mapping, and if so what sort of
     * mapping */
    ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
                    &capabilities);
    if (ret < 0) {
        kleave(" = %d [val]", ret);
        return ret;
    }

    /* we ignore the address hint */
    addr = 0;
    len = PAGE_ALIGN(len);

    /* we've determined that we can make the mapping, now translate what we
     * now know into VMA flags */
    vm_flags = determine_vm_flags(file, prot, flags, capabilities);

    /* we're going to need to record the mapping */
    region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
    if (!region)
        goto error_getting_region;

    vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
    if (!vma)
        goto error_getting_vma;

    region->vm_usage = 1;
    region->vm_flags = vm_flags;
    region->vm_pgoff = pgoff;

    INIT_LIST_HEAD(&vma->anon_vma_chain);
    vma->vm_flags = vm_flags;
    vma->vm_pgoff = pgoff;

    if (file) {
        region->vm_file = get_file(file);
        vma->vm_file = get_file(file);
    }

    down_write(&nommu_region_sem);

    /* if we want to share, we need to check for regions created by other
     * mmap() calls that overlap with our proposed mapping
     * - we can only share with a superset match on most regular files
     * - shared mappings on character devices and memory backed files are
     *   permitted to overlap inexactly as far as we are concerned for in
     *   these cases, sharing is handled in the driver or filesystem rather
     *   than here
     */
    if (vm_flags & VM_MAYSHARE) {
        struct vm_region *pregion;
        unsigned long pglen, rpglen, pgend, rpgend, start;

        pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        pgend = pgoff + pglen;

        for (rb = rb_first(&nommu_region_tree); rb; rb = rb_next(rb)) {
            pregion = rb_entry(rb, struct vm_region, vm_rb);

            if (!(pregion->vm_flags & VM_MAYSHARE))
                continue;

            /* search for overlapping mappings on the same file */
            if (pregion->vm_file->f_path.dentry->d_inode !=
                file->f_path.dentry->d_inode)
                continue;

            if (pregion->vm_pgoff >= pgend)
                continue;

            rpglen = pregion->vm_end - pregion->vm_start;
            rpglen = (rpglen + PAGE_SIZE - 1) >> PAGE_SHIFT;
            rpgend = pregion->vm_pgoff + rpglen;
            if (pgoff >= rpgend)
                continue;

            /* handle inexactly overlapping matches between
             * mappings */
            if ((pregion->vm_pgoff != pgoff || rpglen != pglen) &&
                !(pgoff >= pregion->vm_pgoff && pgend <= rpgend)) {
                /* new mapping is not a subset of the region */
                if (!(capabilities & BDI_CAP_MAP_DIRECT))
                    goto sharing_violation;
                continue;
            }

            /* we've found a region we can share */
            pregion->vm_usage++;
            vma->vm_region = pregion;
            start = pregion->vm_start;
            start += (pgoff - pregion->vm_pgoff) << PAGE_SHIFT;
            vma->vm_start = start;
            vma->vm_end = start + len;

            if (pregion->vm_flags & VM_MAPPED_COPY) {
                kdebug("share copy");
                vma->vm_flags |= VM_MAPPED_COPY;
            } else {
                kdebug("share mmap");
                ret = do_mmap_shared_file(vma);
                if (ret < 0) {
                    vma->vm_region = NULL;
                    vma->vm_start = 0;
                    vma->vm_end = 0;
                    pregion->vm_usage--;
                    pregion = NULL;
                    goto error_just_free;
                }
            }
            fput(region->vm_file);
            kmem_cache_free(vm_region_jar, region);
            region = pregion;
            result = start;
            goto share;
        }

        /* obtain the address at which to make a shared mapping
         * - this is the hook for quasi-memory character devices to
         *   tell us the location of a shared mapping
         */
        if (capabilities & BDI_CAP_MAP_DIRECT) {
            addr = file->f_op->get_unmapped_area(file, addr, len,
                                 pgoff, flags);
            if (IS_ERR_VALUE(addr)) {
                ret = addr;
                if (ret != -ENOSYS)
                    goto error_just_free;

                /* the driver refused to tell us where to site
                 * the mapping so we'll have to attempt to copy
                 * it */
                ret = -ENODEV;
                if (!(capabilities & BDI_CAP_MAP_COPY))
                    goto error_just_free;

                capabilities &= ~BDI_CAP_MAP_DIRECT;
            } else {
                vma->vm_start = region->vm_start = addr;
                vma->vm_end = region->vm_end = addr + len;
            }
        }
    }

    vma->vm_region = region;

    /* set up the mapping
     * - the region is filled in if BDI_CAP_MAP_DIRECT is still set
     */
    if (file && vma->vm_flags & VM_SHARED)
        ret = do_mmap_shared_file(vma);
    else
        ret = do_mmap_private(vma, region, len, capabilities);
    if (ret < 0)
        goto error_just_free;
    add_nommu_region(region);

    /* clear anonymous mappings that don't ask for uninitialized data */
    if (!vma->vm_file && !(flags & MAP_UNINITIALIZED))
        memset((void *)region->vm_start, 0,
               region->vm_end - region->vm_start);

    /* okay... we have a mapping; now we have to register it */
    result = vma->vm_start;

    current->mm->total_vm += len >> PAGE_SHIFT;

share:
    add_vma_to_mm(current->mm, vma);

    /* we flush the region from the icache only when the first executable
     * mapping of it is made  */
    if (vma->vm_flags & VM_EXEC && !region->vm_icache_flushed) {
        flush_icache_range(region->vm_start, region->vm_end);
        region->vm_icache_flushed = true;
    }

    up_write(&nommu_region_sem);

    kleave(" = %lx", result);
    return result;

error_just_free:
    up_write(&nommu_region_sem);
error:
    if (region->vm_file)
        fput(region->vm_file);
    kmem_cache_free(vm_region_jar, region);
    if (vma->vm_file)
        fput(vma->vm_file);
    kmem_cache_free(vm_area_cachep, vma);
    kleave(" = %d", ret);
    return ret;

sharing_violation:
    up_write(&nommu_region_sem);
    printk(KERN_WARNING "Attempt to share mismatched mappings\n");
    ret = -EINVAL;
    goto error;

error_getting_vma:
    kmem_cache_free(vm_region_jar, region);
    printk(KERN_WARNING "Allocation of vma for %lu byte allocation"
           " from process %d failed\n",
           len, current->pid);
    show_free_areas(0);
    return -ENOMEM;

error_getting_region:
    printk(KERN_WARNING "Allocation of vm region for %lu byte allocation"
           " from process %d failed\n",
           len, current->pid);
    show_free_areas(0);
    return -ENOMEM;
}

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
        unsigned long, prot, unsigned long, flags,
        unsigned long, fd, unsigned long, pgoff)
{
    struct file *file = NULL;
    unsigned long retval = -EBADF;

    audit_mmap_fd(fd, flags);
    if (!(flags & MAP_ANONYMOUS)) {
        file = fget(fd);
        if (!file)
            goto out;
    }

    flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);

    retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);

    if (file)
        fput(file);
out:
    return retval;
}

#ifdef __ARCH_WANT_SYS_OLD_MMAP
struct mmap_arg_struct {
    unsigned long addr;
    unsigned long len;
    unsigned long prot;
    unsigned long flags;
    unsigned long fd;
    unsigned long offset;
};

SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
{
    struct mmap_arg_struct a;

    if (copy_from_user(&a, arg, sizeof(a)))
        return -EFAULT;
    if (a.offset & ~PAGE_MASK)
        return -EINVAL;

    return sys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                  a.offset >> PAGE_SHIFT);
}
#endif /* __ARCH_WANT_SYS_OLD_MMAP */

/*
 * split a vma into two pieces at address 'addr', a new vma is allocated either
 * for the first part or the tail.
 */
int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
          unsigned long addr, int new_below)
{
    struct vm_area_struct *new;
    struct vm_region *region;
    unsigned long npages;

    kenter("");

    /* we're only permitted to split anonymous regions (these should have
     * only a single usage on the region) */
    if (vma->vm_file)
        return -ENOMEM;

    if (mm->map_count >= sysctl_max_map_count)
        return -ENOMEM;

    region = kmem_cache_alloc(vm_region_jar, GFP_KERNEL);
    if (!region)
        return -ENOMEM;

    new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
    if (!new) {
        kmem_cache_free(vm_region_jar, region);
        return -ENOMEM;
    }

    /* most fields are the same, copy all, and then fixup */
    *new = *vma;
    *region = *vma->vm_region;
    new->vm_region = region;

    npages = (addr - vma->vm_start) >> PAGE_SHIFT;

    if (new_below) {
        region->vm_top = region->vm_end = new->vm_end = addr;
    } else {
        region->vm_start = new->vm_start = addr;
        region->vm_pgoff = new->vm_pgoff += npages;
    }

    if (new->vm_ops && new->vm_ops->open)
        new->vm_ops->open(new);

    delete_vma_from_mm(vma);
    down_write(&nommu_region_sem);
    delete_nommu_region(vma->vm_region);
    if (new_below) {
        vma->vm_region->vm_start = vma->vm_start = addr;
        vma->vm_region->vm_pgoff = vma->vm_pgoff += npages;
    } else {
        vma->vm_region->vm_end = vma->vm_end = addr;
        vma->vm_region->vm_top = addr;
    }
    add_nommu_region(vma->vm_region);
    add_nommu_region(new->vm_region);
    up_write(&nommu_region_sem);
    add_vma_to_mm(mm, vma);
    add_vma_to_mm(mm, new);
    return 0;
}

/*
 * shrink a VMA by removing the specified chunk from either the beginning or
 * the end
 */
static int shrink_vma(struct mm_struct *mm,
              struct vm_area_struct *vma,
              unsigned long from, unsigned long to)
{
    struct vm_region *region;

    kenter("");

    /* adjust the VMA's pointers, which may reposition it in the MM's tree
     * and list */
    delete_vma_from_mm(vma);
    if (from > vma->vm_start)
        vma->vm_end = from;
    else
        vma->vm_start = to;
    add_vma_to_mm(mm, vma);

    /* cut the backing region down to size */
    region = vma->vm_region;
    BUG_ON(region->vm_usage != 1);

    down_write(&nommu_region_sem);
    delete_nommu_region(region);
    if (from > region->vm_start) {
        to = region->vm_top;
        region->vm_top = region->vm_end = from;
    } else {
        region->vm_start = to;
    }
    add_nommu_region(region);
    up_write(&nommu_region_sem);

    free_page_series(from, to);
    return 0;
}

/*
 * release a mapping
 * - under NOMMU conditions the chunk to be unmapped must be backed by a single
 *   VMA, though it need not cover the whole VMA
 */
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
{
    struct vm_area_struct *vma;
    unsigned long end;
    int ret;

    kenter(",%lx,%zx", start, len);

    len = PAGE_ALIGN(len);
    if (len == 0)
        return -EINVAL;

    end = start + len;

    /* find the first potentially overlapping VMA */
    vma = find_vma(mm, start);
    if (!vma) {
        static int limit = 0;
        if (limit < 5) {
            printk(KERN_WARNING
                   "munmap of memory not mmapped by process %d"
                   " (%s): 0x%lx-0x%lx\n",
                   current->pid, current->comm,
                   start, start + len - 1);
            limit++;
        }
        return -EINVAL;
    }

    /* we're allowed to split an anonymous VMA but not a file-backed one */
    if (vma->vm_file) {
        do {
            if (start > vma->vm_start) {
                kleave(" = -EINVAL [miss]");
                return -EINVAL;
            }
            if (end == vma->vm_end)
                goto erase_whole_vma;
            vma = vma->vm_next;
        } while (vma);
        kleave(" = -EINVAL [split file]");
        return -EINVAL;
    } else {
        /* the chunk must be a subset of the VMA found */
        if (start == vma->vm_start && end == vma->vm_end)
            goto erase_whole_vma;
        if (start < vma->vm_start || end > vma->vm_end) {
            kleave(" = -EINVAL [superset]");
            return -EINVAL;
        }
        if (start & ~PAGE_MASK) {
            kleave(" = -EINVAL [unaligned start]");
            return -EINVAL;
        }
        if (end != vma->vm_end && end & ~PAGE_MASK) {
            kleave(" = -EINVAL [unaligned split]");
            return -EINVAL;
        }
        if (start != vma->vm_start && end != vma->vm_end) {
            ret = split_vma(mm, vma, start, 1);
            if (ret < 0) {
                kleave(" = %d [split]", ret);
                return ret;
            }
        }
        return shrink_vma(mm, vma, start, end);
    }

erase_whole_vma:
    delete_vma_from_mm(vma);
    delete_vma(mm, vma);
    kleave(" = 0");
    return 0;
}
EXPORT_SYMBOL(do_munmap);

int vm_munmap(unsigned long addr, size_t len)
{
    struct mm_struct *mm = current->mm;
    int ret;

    down_write(&mm->mmap_sem);
    ret = do_munmap(mm, addr, len);
    up_write(&mm->mmap_sem);
    return ret;
}
EXPORT_SYMBOL(vm_munmap);

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
    return vm_munmap(addr, len);
}

/*
 * release all the mappings made in a process's VM space
 */
void exit_mmap(struct mm_struct *mm)
{
    struct vm_area_struct *vma;

    if (!mm)
        return;

    kenter("");

    mm->total_vm = 0;

    while ((vma = mm->mmap)) {
        mm->mmap = vma->vm_next;
        delete_vma_from_mm(vma);
        delete_vma(mm, vma);
        cond_resched();
    }

    kleave("");
}

unsigned long vm_brk(unsigned long addr, unsigned long len)
{
    return -ENOMEM;
}

/*
 * expand (or shrink) an existing mapping, potentially moving it at the same
 * time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * under NOMMU conditions, we only permit changing a mapping's size, and only
 * as long as it stays within the region allocated by do_mmap_private() and the
 * block is not shareable
 *
 * MREMAP_FIXED is not supported under NOMMU conditions
 */
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;

    /* insanity checks first */
    old_len = PAGE_ALIGN(old_len);
    new_len = PAGE_ALIGN(new_len);
    if (old_len == 0 || new_len == 0)
        return (unsigned long) -EINVAL;

    if (addr & ~PAGE_MASK)
        return -EINVAL;

    if (flags & MREMAP_FIXED && new_addr != addr)
        return (unsigned long) -EINVAL;

    vma = find_vma_exact(current->mm, addr, old_len);
    if (!vma)
        return (unsigned long) -EINVAL;

    if (vma->vm_end != vma->vm_start + old_len)
        return (unsigned long) -EFAULT;

    if (vma->vm_flags & VM_MAYSHARE)
        return (unsigned long) -EPERM;

    if (new_len > vma->vm_region->vm_end - vma->vm_region->vm_start)
        return (unsigned long) -ENOMEM;

    /* all checks complete - do it */
    vma->vm_end = vma->vm_start + new_len;
    return vma->vm_start;
}
EXPORT_SYMBOL(do_mremap);

SYSCALL_DEFINE5(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;
}

struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
            unsigned int foll_flags)
{
    return NULL;
}

int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
        unsigned long pfn, unsigned long size, pgprot_t prot)
{
    if (addr != (pfn << PAGE_SHIFT))
        return -EINVAL;

    vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
    return 0;
}
EXPORT_SYMBOL(remap_pfn_range);

int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
            unsigned long pgoff)
{
    unsigned int size = vma->vm_end - vma->vm_start;

    if (!(vma->vm_flags & VM_USERMAP))
        return -EINVAL;

    vma->vm_start = (unsigned long)(addr + (pgoff << PAGE_SHIFT));
    vma->vm_end = vma->vm_start + size;

    return 0;
}
EXPORT_SYMBOL(remap_vmalloc_range);

unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
    unsigned long len, unsigned long pgoff, unsigned long flags)
{
    return -ENOMEM;
}

void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
{
}

void unmap_mapping_range(struct address_space *mapping,
             loff_t const holebegin, loff_t const holelen,
             int even_cows)
{
}
EXPORT_SYMBOL(unmap_mapping_range);

/*
 * Check that a process has enough memory to allocate a new virtual
 * mapping. 0 means there is enough memory for the allocation to
 * succeed and -ENOMEM implies there is not.
 *
 * We currently support three overcommit policies, which are set via the
 * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
 *
 * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
 * Additional code 2002 Jul 20 by Robert Love.
 *
 * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
 *
 * Note this is a helper function intended to be used by LSMs which
 * wish to use this logic.
 */
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
    unsigned long free, allowed;

    vm_acct_memory(pages);

    /*
     * Sometimes we want to use more memory than we have
     */
    if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
        return 0;

    if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
        free = global_page_state(NR_FREE_PAGES);
        free += global_page_state(NR_FILE_PAGES);

        /*
         * shmem pages shouldn't be counted as free in this
         * case, they can't be purged, only swapped out, and
         * that won't affect the overall amount of available
         * memory in the system.
         */
        free -= global_page_state(NR_SHMEM);

        free += nr_swap_pages;

        /*
         * Any slabs which are created with the
         * SLAB_RECLAIM_ACCOUNT flag claim to have contents
         * which are reclaimable, under pressure.  The dentry
         * cache and most inode caches should fall into this
         */
        free += global_page_state(NR_SLAB_RECLAIMABLE);

        /*
         * Leave reserved pages. The pages are not for anonymous pages.
         */
        if (free <= totalreserve_pages)
            goto error;
        else
            free -= totalreserve_pages;

        /*
         * Leave the last 3% for root
         */
        if (!cap_sys_admin)
            free -= free / 32;

        if (free > pages)
            return 0;

        goto error;
    }

    allowed = totalram_pages * sysctl_overcommit_ratio / 100;
    /*
     * Leave the last 3% for root
     */
    if (!cap_sys_admin)
        allowed -= allowed / 32;
    allowed += total_swap_pages;

    /* Don't let a single process grow too big:
       leave 3% of the size of this process for other processes */
    if (mm)
        allowed -= mm->total_vm / 32;

    if (percpu_counter_read_positive(&vm_committed_as) < allowed)
        return 0;

error:
    vm_unacct_memory(pages);

    return -ENOMEM;
}

int in_gate_area_no_mm(unsigned long addr)
{
    return 0;
}

int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
    BUG();
    return 0;
}
EXPORT_SYMBOL(filemap_fault);

int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
                 unsigned long size, pgoff_t pgoff)
{
    BUG();
    return 0;
}
EXPORT_SYMBOL(generic_file_remap_pages);

static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
        unsigned long addr, void *buf, int len, int write)
{
    struct vm_area_struct *vma;

    down_read(&mm->mmap_sem);

    /* the access must start within one of the target process's mappings */
    vma = find_vma(mm, addr);
    if (vma) {
        /* don't overrun this mapping */
        if (addr + len >= vma->vm_end)
            len = vma->vm_end - addr;

        /* only read or write mappings where it is permitted */
        if (write && vma->vm_flags & VM_MAYWRITE)
            copy_to_user_page(vma, NULL, addr,
                     (void *) addr, buf, len);
        else if (!write && vma->vm_flags & VM_MAYREAD)
            copy_from_user_page(vma, NULL, addr,
                        buf, (void *) addr, len);
        else
            len = 0;
    } else {
        len = 0;
    }

    up_read(&mm->mmap_sem);

    return len;
}

int access_remote_vm(struct mm_struct *mm, unsigned long addr,
        void *buf, int len, int write)
{
    return __access_remote_vm(NULL, mm, addr, buf, len, write);
}

/*
 * Access another process' address space.
 * - source/target buffer must be kernel space
 */
int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
{
    struct mm_struct *mm;

    if (addr + len < addr)
        return 0;

    mm = get_task_mm(tsk);
    if (!mm)
        return 0;

    len = __access_remote_vm(tsk, mm, addr, buf, len, write);

    mmput(mm);
    return len;
}

int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
                size_t newsize)
{
    struct vm_area_struct *vma;
    struct vm_region *region;
    pgoff_t low, high;
    size_t r_size, r_top;

    low = newsize >> PAGE_SHIFT;
    high = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;

    down_write(&nommu_region_sem);
    mutex_lock(&inode->i_mapping->i_mmap_mutex);

    /* search for VMAs that fall within the dead zone */
    vma_interval_tree_foreach(vma, &inode->i_mapping->i_mmap, low, high) {
        /* found one - only interested if it's shared out of the page
         * cache */
        if (vma->vm_flags & VM_SHARED) {
            mutex_unlock(&inode->i_mapping->i_mmap_mutex);
            up_write(&nommu_region_sem);
            return -ETXTBSY; /* not quite true, but near enough */
        }
    }

    /* reduce any regions that overlap the dead zone - if in existence,
     * these will be pointed to by VMAs that don't overlap the dead zone
     *
     * we don't check for any regions that start beyond the EOF as there
     * shouldn't be any
     */
    vma_interval_tree_foreach(vma, &inode->i_mapping->i_mmap,
                  0, ULONG_MAX) {
        if (!(vma->vm_flags & VM_SHARED))
            continue;

        region = vma->vm_region;
        r_size = region->vm_top - region->vm_start;
        r_top = (region->vm_pgoff << PAGE_SHIFT) + r_size;

        if (r_top > newsize) {
            region->vm_top -= r_top - newsize;
            if (region->vm_end > region->vm_top)
                region->vm_end = region->vm_top;
        }
    }

    mutex_unlock(&inode->i_mapping->i_mmap_mutex);
    up_write(&nommu_region_sem);
    return 0;
}