Merge tag 'io_uring-6.9-20240412' of git://git.kernel.dk/linux

[thirdparty/linux.git] / mm / nommu.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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/admin-guide/mm/nommu-mmap.rst
 *
 *  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>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/export.h>
#include <linux/mm.h>
#include <linux/sched/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/backing-dev.h>
#include <linux/compiler.h>
#include <linux/mount.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/printk.h>

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

void *high_memory;
EXPORT_SYMBOL(high_memory);
struct page *mem_map;
unsigned long max_mapnr;
EXPORT_SYMBOL(max_mapnr);
unsigned long highest_memmap_pfn;
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);

/* 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(page);
}

/**
 * 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);

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

void *__vmalloc(unsigned long size, gfp_t gfp_mask)
{
        /*
         *  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_node_range(unsigned long size, unsigned long align,
                unsigned long start, unsigned long end, gfp_t gfp_mask,
                pgprot_t prot, unsigned long vm_flags, int node,
                const void *caller)
{
        return __vmalloc(size, gfp_mask);
}

void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
                int node, const void *caller)
{
        return __vmalloc(size, gfp_mask);
}

static void *__vmalloc_user_flags(unsigned long size, gfp_t flags)
{
        void *ret;

        ret = __vmalloc(size, flags);
        if (ret) {
                struct vm_area_struct *vma;

                mmap_write_lock(current->mm);
                vma = find_vma(current->mm, (unsigned long)ret);
                if (vma)
                        vm_flags_set(vma, VM_USERMAP);
                mmap_write_unlock(current->mm);
        }

        return ret;
}

void *vmalloc_user(unsigned long size)
{
        return __vmalloc_user_flags(size, GFP_KERNEL | __GFP_ZERO);
}
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_iter(struct iov_iter *iter, const char *addr, size_t count)
{
        /* Don't allow overflow */
        if ((unsigned long) addr + count < count)
                count = -(unsigned long) addr;

        return copy_to_iter(addr, count, iter);
}

/*
 *      vmalloc  -  allocate virtually contiguous memory
 *
 *      @size:          allocation size
 *
 *      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(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL);
}
EXPORT_SYMBOL(vmalloc);

void *vmalloc_huge(unsigned long size, gfp_t gfp_mask) __weak __alias(__vmalloc);

/*
 *      vzalloc - allocate virtually contiguous memory with zero fill
 *
 *      @size:          allocation size
 *
 *      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(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL | __GFP_ZERO);
}
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);

/**
 * 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 contiguous kernel virtual space.
 */
void *vmalloc_32(unsigned long size)
{
        return __vmalloc(size, GFP_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)
{
        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);

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);

int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
                        unsigned long num)
{
        return -EINVAL;
}
EXPORT_SYMBOL(vm_map_pages);

int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
                                unsigned long num)
{
        return -EINVAL;
}
EXPORT_SYMBOL(vm_map_pages_zero);

/*
 *  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_user_range(mm->brk, brk);
        return mm->brk = brk;
}

/*
 * initialise the percpu counter for VM and region record slabs
 */
void __init mmap_init(void)
{
        int ret;

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

/*
 * 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(last->vm_end <= last->vm_start);
        BUG_ON(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(region->vm_end <= region->vm_start);
                BUG_ON(region->vm_top < region->vm_end);
                BUG_ON(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((void *)from);

                atomic_long_dec(&mmap_pages_allocated);
                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)
{
        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)
                        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);
}

static void setup_vma_to_mm(struct vm_area_struct *vma, struct mm_struct *mm)
{
        vma->vm_mm = mm;

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

                i_mmap_lock_write(mapping);
                flush_dcache_mmap_lock(mapping);
                vma_interval_tree_insert(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
                i_mmap_unlock_write(mapping);
        }
}

static void cleanup_vma_from_mm(struct vm_area_struct *vma)
{
        vma->vm_mm->map_count--;
        /* remove the VMA from the mapping */
        if (vma->vm_file) {
                struct address_space *mapping;
                mapping = vma->vm_file->f_mapping;

                i_mmap_lock_write(mapping);
                flush_dcache_mmap_lock(mapping);
                vma_interval_tree_remove(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
                i_mmap_unlock_write(mapping);
        }
}

/*
 * delete a VMA from its owning mm_struct and address space
 */
static int delete_vma_from_mm(struct vm_area_struct *vma)
{
        VMA_ITERATOR(vmi, vma->vm_mm, vma->vm_start);

        vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma)) {
                pr_warn("Allocation of vma tree for process %d failed\n",
                       current->pid);
                return -ENOMEM;
        }
        cleanup_vma_from_mm(vma);

        /* remove from the MM's tree and list */
        vma_iter_clear(&vmi);
        return 0;
}
/*
 * destroy a VMA record
 */
static void delete_vma(struct mm_struct *mm, struct vm_area_struct *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);
        vm_area_free(vma);
}

struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
                                             unsigned long start_addr,
                                             unsigned long end_addr)
{
        unsigned long index = start_addr;

        mmap_assert_locked(mm);
        return mt_find(&mm->mm_mt, &index, end_addr - 1);
}
EXPORT_SYMBOL(find_vma_intersection);

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

        return vma_iter_load(&vmi);
}
EXPORT_SYMBOL(find_vma);

/*
 * At least xtensa ends up having protection faults even with no
 * MMU.. No stack expansion, at least.
 */
struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
                        unsigned long addr, struct pt_regs *regs)
{
        struct vm_area_struct *vma;

        mmap_read_lock(mm);
        vma = vma_lookup(mm, addr);
        if (!vma)
                mmap_read_unlock(mm);
        return vma;
}

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

struct vm_area_struct *expand_stack(struct mm_struct *mm, unsigned long addr)
{
        mmap_read_unlock(mm);
        return NULL;
}

/*
 * look up the first VMA exactly that exactly matches addr
 * - should be called with mm->mmap_lock 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;
        VMA_ITERATOR(vmi, mm, addr);

        vma = vma_iter_load(&vmi);
        if (!vma)
                return NULL;
        if (vma->vm_start != addr)
                return NULL;
        if (vma->vm_end != end)
                return NULL;

        return vma;
}

/*
 * 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)
                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) {
                /* files must support mmap */
                if (!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
                 */
                if (file->f_op->mmap_capabilities) {
                        capabilities = file->f_op->mmap_capabilities(file);
                } else {
                        /* no explicit capabilities set, so assume some
                         * defaults */
                        switch (file_inode(file)->i_mode & S_IFMT) {
                        case S_IFREG:
                        case S_IFBLK:
                                capabilities = NOMMU_MAP_COPY;
                                break;

                        case S_IFCHR:
                                capabilities =
                                        NOMMU_MAP_DIRECT |
                                        NOMMU_MAP_READ |
                                        NOMMU_MAP_WRITE;
                                break;

                        default:
                                return -EINVAL;
                        }
                }

                /* eliminate any capabilities that we can't support on this
                 * device */
                if (!file->f_op->get_unmapped_area)
                        capabilities &= ~NOMMU_MAP_DIRECT;
                if (!(file->f_mode & FMODE_CAN_READ))
                        capabilities &= ~NOMMU_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 (!(capabilities & NOMMU_MAP_DIRECT))
                                return -ENODEV;

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

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

                if (capabilities & NOMMU_MAP_DIRECT) {
                        if (((prot & PROT_READ)  && !(capabilities & NOMMU_MAP_READ))  ||
                            ((prot & PROT_WRITE) && !(capabilities & NOMMU_MAP_WRITE)) ||
                            ((prot & PROT_EXEC)  && !(capabilities & NOMMU_MAP_EXEC))
                            ) {
                                capabilities &= ~NOMMU_MAP_DIRECT;
                                if (flags & MAP_SHARED) {
                                        pr_warn("MAP_SHARED not completely supported on !MMU\n");
                                        return -EINVAL;
                                }
                        }
                }

                /* handle executable mappings and implied executable
                 * mappings */
                if (path_noexec(&file->f_path)) {
                        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 & NOMMU_MAP_EXEC)
                                        prot |= PROT_EXEC;
                        }
                } else if ((prot & PROT_READ) &&
                         (prot & PROT_EXEC) &&
                         !(capabilities & NOMMU_MAP_EXEC)
                         ) {
                        /* backing file is not executable, try to copy */
                        capabilities &= ~NOMMU_MAP_DIRECT;
                }
        } else {
                /* anonymous mappings are always memory backed and can be
                 * privately mapped
                 */
                capabilities = NOMMU_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, 0) | calc_vm_flag_bits(flags);

        if (!file) {
                /*
                 * MAP_ANONYMOUS. MAP_SHARED is mapped to MAP_PRIVATE, because
                 * there is no fork().
                 */
                vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
        } else if (flags & MAP_PRIVATE) {
                /* MAP_PRIVATE file mapping */
                if (capabilities & NOMMU_MAP_DIRECT)
                        vm_flags |= (capabilities & NOMMU_VMFLAGS);
                else
                        vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

                if (!(prot & PROT_WRITE) && !current->ptrace)
                        /*
                         * R/O private file mapping which cannot be used to
                         * modify memory, especially also not via active ptrace
                         * (e.g., set breakpoints) or later by upgrading
                         * permissions (no mprotect()). We can try overlaying
                         * the file mapping, which will work e.g., on chardevs,
                         * ramfs/tmpfs/shmfs and romfs/cramf.
                         */
                        vm_flags |= VM_MAYOVERLAY;
        } else {
                /* MAP_SHARED file mapping: NOMMU_MAP_DIRECT is set. */
                vm_flags |= VM_SHARED | VM_MAYSHARE |
                            (capabilities & NOMMU_VMFLAGS);
        }

        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 = call_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)
{
        unsigned long total, point;
        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_MAYOVERLAY will be set if
         * it may attempt to share, which will make is_nommu_shared_mapping()
         * happy.
         */
        if (capabilities & NOMMU_MAP_DIRECT) {
                ret = call_mmap(vma->vm_file, vma);
                /* shouldn't return success if we're not sharing */
                if (WARN_ON_ONCE(!is_nommu_shared_mapping(vma->vm_flags)))
                        ret = -ENOSYS;
                if (ret == 0) {
                        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);
        total = 1 << order;
        point = len >> PAGE_SHIFT;

        /* we don't want to allocate a power-of-2 sized page set */
        if (sysctl_nr_trim_pages && total - point >= sysctl_nr_trim_pages)
                total = point;

        base = alloc_pages_exact(total << PAGE_SHIFT, GFP_KERNEL);
        if (!base)
                goto enomem;

        atomic_long_add(total, &mmap_pages_allocated);

        vm_flags_set(vma, VM_MAPPED_COPY);
        region->vm_flags = vma->vm_flags;
        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 */
                loff_t fpos;

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

                ret = kernel_read(vma->vm_file, base, len, &fpos);
                if (ret < 0)
                        goto error_free;

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

        } else {
                vma_set_anonymous(vma);
        }

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

/*
 * handle mapping creation for uClinux
 */
unsigned long do_mmap(struct file *file,
                        unsigned long addr,
                        unsigned long len,
                        unsigned long prot,
                        unsigned long flags,
                        vm_flags_t vm_flags,
                        unsigned long pgoff,
                        unsigned long *populate,
                        struct list_head *uf)
{
        struct vm_area_struct *vma;
        struct vm_region *region;
        struct rb_node *rb;
        unsigned long capabilities, result;
        int ret;
        VMA_ITERATOR(vmi, current->mm, 0);

        *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)
                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 = vm_area_alloc(current->mm);
        if (!vma)
                goto error_getting_vma;

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

        vm_flags_init(vma, 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 (is_nommu_shared_mapping(vm_flags)) {
                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 (!is_nommu_shared_mapping(pregion->vm_flags))
                                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 & NOMMU_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)
                                vm_flags_set(vma, VM_MAPPED_COPY);
                        else {
                                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 & NOMMU_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 & NOMMU_MAP_COPY))
                                        goto error_just_free;

                                capabilities &= ~NOMMU_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 NOMMU_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 &&
            (!IS_ENABLED(CONFIG_MMAP_ALLOW_UNINITIALIZED) ||
             !(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:
        BUG_ON(!vma->vm_region);
        vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma))
                goto error_just_free;

        setup_vma_to_mm(vma, current->mm);
        current->mm->map_count++;
        /* add the VMA to the tree */
        vma_iter_store(&vmi, 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_user_range(region->vm_start, region->vm_end);
                region->vm_icache_flushed = true;
        }

        up_write(&nommu_region_sem);

        return result;

error_just_free:
        up_write(&nommu_region_sem);
error:
        vma_iter_free(&vmi);
        if (region->vm_file)
                fput(region->vm_file);
        kmem_cache_free(vm_region_jar, region);
        if (vma->vm_file)
                fput(vma->vm_file);
        vm_area_free(vma);
        return ret;

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

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

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

unsigned long ksys_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;
        }

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

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

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
                unsigned long, prot, unsigned long, flags,
                unsigned long, fd, unsigned long, pgoff)
{
        return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
}

#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 (offset_in_page(a.offset))
                return -EINVAL;

        return ksys_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.
 */
static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
                     unsigned long addr, int new_below)
{
        struct vm_area_struct *new;
        struct vm_region *region;
        unsigned long npages;
        struct mm_struct *mm;

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

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

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

        new = vm_area_dup(vma);
        if (!new)
                goto err_vma_dup;

        /* most fields are the same, copy all, and then fixup */
        *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;
        }

        vma_iter_config(vmi, new->vm_start, new->vm_end);
        if (vma_iter_prealloc(vmi, vma)) {
                pr_warn("Allocation of vma tree for process %d failed\n",
                        current->pid);
                goto err_vmi_preallocate;
        }

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

        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);

        setup_vma_to_mm(vma, mm);
        setup_vma_to_mm(new, mm);
        vma_iter_store(vmi, new);
        mm->map_count++;
        return 0;

err_vmi_preallocate:
        vm_area_free(new);
err_vma_dup:
        kmem_cache_free(vm_region_jar, region);
        return -ENOMEM;
}

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

        /* adjust the VMA's pointers, which may reposition it in the MM's tree
         * and list */
        if (from > vma->vm_start) {
                if (vma_iter_clear_gfp(vmi, from, vma->vm_end, GFP_KERNEL))
                        return -ENOMEM;
                vma->vm_end = from;
        } else {
                if (vma_iter_clear_gfp(vmi, vma->vm_start, to, GFP_KERNEL))
                        return -ENOMEM;
                vma->vm_start = to;
        }

        /* 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 list_head *uf)
{
        VMA_ITERATOR(vmi, mm, start);
        struct vm_area_struct *vma;
        unsigned long end;
        int ret = 0;

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

        end = start + len;

        /* find the first potentially overlapping VMA */
        vma = vma_find(&vmi, end);
        if (!vma) {
                static int limit;
                if (limit < 5) {
                        pr_warn("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)
                                return -EINVAL;
                        if (end == vma->vm_end)
                                goto erase_whole_vma;
                        vma = vma_find(&vmi, end);
                } while (vma);
                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)
                        return -EINVAL;
                if (offset_in_page(start))
                        return -EINVAL;
                if (end != vma->vm_end && offset_in_page(end))
                        return -EINVAL;
                if (start != vma->vm_start && end != vma->vm_end) {
                        ret = split_vma(&vmi, vma, start, 1);
                        if (ret < 0)
                                return ret;
                }
                return vmi_shrink_vma(&vmi, vma, start, end);
        }

erase_whole_vma:
        if (delete_vma_from_mm(vma))
                ret = -ENOMEM;
        else
                delete_vma(mm, vma);
        return ret;
}

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

        mmap_write_lock(mm);
        ret = do_munmap(mm, addr, len, NULL);
        mmap_write_unlock(mm);
        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)
{
        VMA_ITERATOR(vmi, mm, 0);
        struct vm_area_struct *vma;

        if (!mm)
                return;

        mm->total_vm = 0;

        /*
         * Lock the mm to avoid assert complaining even though this is the only
         * user of the mm
         */
        mmap_write_lock(mm);
        for_each_vma(vmi, vma) {
                cleanup_vma_from_mm(vma);
                delete_vma(mm, vma);
                cond_resched();
        }
        __mt_destroy(&mm->mm_mt);
        mmap_write_unlock(mm);
}

/*
 * 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 (offset_in_page(addr))
                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 (is_nommu_shared_mapping(vma->vm_flags))
                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;

        mmap_write_lock(current->mm);
        ret = do_mremap(addr, old_len, new_len, flags, new_addr);
        mmap_write_unlock(current->mm);
        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;

        vm_flags_set(vma, 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);

vm_fault_t filemap_fault(struct vm_fault *vmf)
{
        BUG();
        return 0;
}
EXPORT_SYMBOL(filemap_fault);

vm_fault_t filemap_map_pages(struct vm_fault *vmf,
                pgoff_t start_pgoff, pgoff_t end_pgoff)
{
        BUG();
        return 0;
}
EXPORT_SYMBOL(filemap_map_pages);

static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
                              void *buf, int len, unsigned int gup_flags)
{
        struct vm_area_struct *vma;
        int write = gup_flags & FOLL_WRITE;

        if (mmap_read_lock_killable(mm))
                return 0;

        /* 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;
        }

        mmap_read_unlock(mm);

        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
 * @gup_flags:  flags modifying lookup behaviour
 *
 * The caller must hold a reference on @mm.
 */
int access_remote_vm(struct mm_struct *mm, unsigned long addr,
                void *buf, int len, unsigned int gup_flags)
{
        return __access_remote_vm(mm, addr, buf, len, gup_flags);
}

/*
 * 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,
                unsigned int gup_flags)
{
        struct mm_struct *mm;

        if (addr + len < addr)
                return 0;

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

        len = __access_remote_vm(mm, addr, buf, len, gup_flags);

        mmput(mm);
        return len;
}
EXPORT_SYMBOL_GPL(access_process_vm);

/**
 * 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 any outstanding VMAs aren't broken and then shrink the
 * vm_regions that extend beyond so that do_mmap() 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);
        i_mmap_lock_read(inode->i_mapping);

        /* 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) {
                        i_mmap_unlock_read(inode->i_mapping);
                        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;
                }
        }

        i_mmap_unlock_read(inode->i_mapping);
        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 = K(global_zone_page_state(NR_FREE_PAGES));

        sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
        return 0;
}
subsys_initcall(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 = K(global_zone_page_state(NR_FREE_PAGES));

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