/*
 *  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 <dhowells@redhat.com>
 *  Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
 *  Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
 *  Copyright (c) 2002      Greg Ungerer <gerg@snapgear.com>
 *  Copyright (c) 2007-2010 Paul Mundt <lethal@linux-sh.org>
 */

#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 <linux/sched/sysctl.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;
unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */
int heap_stack_gap = 0;

atomic_long_t mmap_pages_allocated;

/*
 * The global memory commitment made in the system can be a metric
 * that can be used to drive ballooning decisions when Linux is hosted
 * as a guest. On Hyper-V, the host implements a policy engine for dynamically
 * balancing memory across competing virtual machines that are hosted.
 * Several metrics drive this policy engine including the guest reported
 * memory commitment.
 */
unsigned long vm_memory_committed(void)
{
        return percpu_counter_read_positive(&vm_committed_as);
}

EXPORT_SYMBOL_GPL(vm_memory_committed);

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);
}

long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                      unsigned long start, unsigned long nr_pages,
                      unsigned int foll_flags, struct page **pages,
                      struct vm_area_struct **vmas, int *nonblocking)
{
        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
 */
long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                    unsigned long start, unsigned long 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);

/**
 * follow_pfn - look up PFN at a user virtual address
 * @vma: memory mapping
 * @address: user virtual address
 * @pfn: location to store found PFN
 *
 * Only IO mappings and raw PFN mappings are allowed.
 *
 * Returns zero and the pfn at @pfn on success, -ve otherwise.
 */
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);

LIST_HEAD(vmap_area_list);

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);

/**
 * vmalloc_node - allocate memory on a specific node
 * @size:       allocation size
 * @node:       numa node
 *
 * Allocate enough pages to cover @size from the page level
 * allocator and map them into contiguous kernel virtual space.
 *
 * For tight control over page level allocator and protection flags
 * use __vmalloc() instead.
 */
void *vmalloc_node(unsigned long size, int node)
{
        return vmalloc(size);
}
EXPORT_SYMBOL(vmalloc_node);

/**
 * vzalloc_node - allocate memory on a specific node with zero fill
 * @size:       allocation size
 * @node:       numa node
 *
 * Allocate enough pages to cover @size from the page level
 * allocator and map them into contiguous 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_node(unsigned long size, int node)
{
        return vzalloc(size);
}
EXPORT_SYMBOL(vzalloc_node);

#ifndef PAGE_KERNEL_EXEC
# define PAGE_KERNEL_EXEC PAGE_KERNEL
#endif

/**
 *      vmalloc_exec  -  allocate virtually contiguous, executable memory
 *      @size:          allocation size
 *
 *      Kernel-internal function to allocate enough pages to cover @size
 *      the page level allocator and map them into contiguous and
 *      executable kernel virtual space.
 *
 *      For tight control over page level allocator and protection flags
 *      use __vmalloc() instead.
 */

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

/**
 * vmalloc_32  -  allocate virtually contiguous memory (32bit addressable)
 *      @size:          allocation size
 *
 *      Allocate enough 32bit PA addressable pages to cover @size from the
 *      page level allocator and map them into continguos kernel virtual space.
 */
void *vmalloc_32(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc_32);

/**
 * vmalloc_32_user - allocate zeroed virtually contiguous 32bit memory
 *      @size:          allocation size
 *
 * The resulting memory area is 32bit addressable and zeroed so it can be
 * mapped to userspace without leaking data.
 *
 * VM_USERMAP is set on the corresponding VMA so that subsequent calls to
 * remap_vmalloc_range() are permissible.
 */
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)
{
}

/**
 *      alloc_vm_area - allocate a range of kernel address space
 *      @size:          size of the area
 *
 *      Returns:        NULL on failure, vm_struct on success
 *
 *      This function reserves a range of kernel address space, and
 *      allocates pagetables to map that range.  No actual mappings
 *      are created.  If the kernel address space is not shared
 *      between processes, it syncs the pagetable across all
 *      processes.
 */
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 = ACCESS_ONCE(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_inode(file)->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_inode(file)->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_inode(file)) &&
                            (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        if (locks_verify_locked(file_inode(file)))
                                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,
                            unsigned long *populate)
{
        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);

        *populate = 0;

        /* 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 (file_inode(pregion->vm_file) !=
                            file_inode(file))
                                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
 */
static 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;
}

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_mask(struct vm_area_struct *vma,
                              unsigned long address, unsigned int flags,
                              unsigned int *page_mask)
{
        *page_mask = 0;
        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 vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
{
        unsigned long pfn = start >> PAGE_SHIFT;
        unsigned long vm_len = vma->vm_end - vma->vm_start;

        pfn += vma->vm_pgoff;
        return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
}
EXPORT_SYMBOL(vm_iomap_memory);

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, reserve;

        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 += get_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;

                /*
                 * Reserve some for root
                 */
                if (!cap_sys_admin)
                        free -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);

                if (free > pages)
                        return 0;

                goto error;
        }

        allowed = totalram_pages * sysctl_overcommit_ratio / 100;
        /*
         * Reserve some 3% for root
         */
        if (!cap_sys_admin)
                allowed -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
        allowed += total_swap_pages;

        /*
         * Don't let a single process grow so big a user can't recover
         */
        if (mm) {
                reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);
                allowed -= min(mm->total_vm / 32, reserve);
        }

        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;
}

/**
 * @access_remote_vm - access another process' address space
 * @mm:         the mm_struct of the target address space
 * @addr:       start address to access
 * @buf:        source or destination buffer
 * @len:        number of bytes to transfer
 * @write:      whether the access is a write
 *
 * The caller must hold a reference on @mm.
 */
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;
}

/**
 * nommu_shrink_inode_mappings - Shrink the shared mappings on an inode
 * @inode: The inode to check
 * @size: The current filesize of the inode
 * @newsize: The proposed filesize of the inode
 *
 * Check the shared mappings on an inode on behalf of a shrinking truncate to
 * make sure that that any outstanding VMAs aren't broken and then shrink the
 * vm_regions that extend that beyond so that do_mmap_pgoff() doesn't
 * automatically grant mappings that are too large.
 */
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;
}

/*
 * Initialise sysctl_user_reserve_kbytes.
 *
 * This is intended to prevent a user from starting a single memory hogging
 * process, such that they cannot recover (kill the hog) in OVERCOMMIT_NEVER
 * mode.
 *
 * The default value is min(3% of free memory, 128MB)
 * 128MB is enough to recover with sshd/login, bash, and top/kill.
 */
static int __meminit init_user_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = global_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);

        sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
        return 0;
}
module_init(init_user_reserve)

/*
 * Initialise sysctl_admin_reserve_kbytes.
 *
 * The purpose of sysctl_admin_reserve_kbytes is to allow the sys admin
 * to log in and kill a memory hogging process.
 *
 * Systems with more than 256MB will reserve 8MB, enough to recover
 * with sshd, bash, and top in OVERCOMMIT_GUESS. Smaller systems will
 * only reserve 3% of free pages by default.
 */
static int __meminit init_admin_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = global_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);

        sysctl_admin_reserve_kbytes = min(free_kbytes / 32, 1UL << 13);
        return 0;
}
module_init(init_admin_reserve)