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 // 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/vmacache.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 <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);
 
 LIST_HEAD(vmap_area_list);
 
 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)
             vma->vm_flags |= 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(char *buf, char *addr, unsigned long count)
 {
     /* Don't allow overflow */
     if ((unsigned long) buf + count < count)
         count = -(unsigned long) buf;
 
     memcpy(buf, addr, count);
     return count;
 }
 
 /*
  *  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);
 }
 
 /*
  * 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_lock 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;
 
     BUG_ON(!vma->vm_region);
 
     mm->map_count++;
     vma->vm_mm = mm;
 
     /* add the VMA to the mapping */
     if (vma->vm_file) {
         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);
     }
 
     /* 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);
 }
 
 /*
  * delete a VMA from its owning mm_struct and address space
  */
 static void delete_vma_from_mm(struct vm_area_struct *vma)
 {
     int i;
     struct address_space *mapping;
     struct mm_struct *mm = vma->vm_mm;
     struct task_struct *curr = current;
 
     mm->map_count--;
     for (i = 0; i < VMACACHE_SIZE; i++) {
         /* if the vma is cached, invalidate the entire cache */
         if (curr->vmacache.vmas[i] == vma) {
             vmacache_invalidate(mm);
             break;
         }
     }
 
     /* remove the VMA from the mapping */
     if (vma->vm_file) {
         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);
     }
 
     /* remove from the MM's tree and list */
     rb_erase(&vma->vm_rb, &mm->mm_rb);
 
     __vma_unlink_list(mm, vma);
 }
 
 /*
  * 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);
 }
 
 /*
  * 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)
 {
     struct vm_area_struct *vma;
 
     /* check the cache first */
     vma = vmacache_find(mm, addr);
     if (likely(vma))
         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) {
             vmacache_update(addr, 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_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;
 
     /* check the cache first */
     vma = vmacache_find_exact(mm, addr, end);
     if (vma)
         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) {
             vmacache_update(addr, 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)
         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);
     /* vm_flags |= mm->def_flags; */
 
     if (!(capabilities & NOMMU_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 & NOMMU_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 = 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_MAYSHARE will be set if it may attempt to share
      */
     if (capabilities & NOMMU_MAP_DIRECT) {
         ret = call_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);
     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);
 
     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 */
         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_free_areas(0, NULL);
     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,
             unsigned long pgoff,
             unsigned long *populate,
             struct list_head *uf)
 {
     struct vm_area_struct *vma;
     struct vm_region *region;
     struct rb_node *rb;
     vm_flags_t vm_flags;
     unsigned long capabilities, result;
     int ret;
 
     *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;
 
     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 & 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)
                 vma->vm_flags |= 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:
     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_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:
     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_free_areas(0, NULL);
     return -ENOMEM;
 
 error_getting_region:
     pr_warn("Allocation of vm region for %lu byte allocation from process %d failed\n",
             len, current->pid);
     show_free_areas(0, NULL);
     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.
  */
 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;
 
     /* 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 = vm_area_dup(vma);
     if (!new) {
         kmem_cache_free(vm_region_jar, region);
         return -ENOMEM;
     }
 
     /* 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;
     }
 
     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;
 
     /* 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 list_head *uf)
 {
     struct vm_area_struct *vma;
     unsigned long end;
     int ret;
 
     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;
         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->vm_next;
         } 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(mm, vma, start, 1);
             if (ret < 0)
                 return ret;
         }
         return shrink_vma(mm, vma, start, end);
     }
 
 erase_whole_vma:
     delete_vma_from_mm(vma);
     delete_vma(mm, vma);
     return 0;
 }
 
 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)
 {
     struct vm_area_struct *vma;
 
     if (!mm)
         return;
 
     mm->total_vm = 0;
 
     while ((vma = mm->mmap)) {
         mm->mmap = vma->vm_next;
         delete_vma_from_mm(vma);
         delete_vma(mm, vma);
         cond_resched();
     }
 }
 
 int 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 (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 (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;
 
     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;
 
     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);
 
 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);
 
 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 = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
 
     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 = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
 
     sysctl_admin_reserve_kbytes = min(free_kbytes / 32, 1UL << 13);
     return 0;
 }
 subsys_initcall(init_admin_reserve);

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