// SPDX-License-Identifier: GPL-2.0-only

  #include <linux/mm.h>

  #include <linux/slab.h>
  #include <linux/string.h>

  #include <linux/compiler.h>

  #include <linux/export.h>

  #include <linux/err.h>

  #include <linux/sched.h>

  #include <linux/sched/mm.h>

  #include <linux/sched/signal.h>

  #include <linux/sched/task_stack.h>

  #include <linux/security.h>

  #include <linux/swap.h>

  #include <linux/swapops.h>

  #include <linux/mman.h>
  #include <linux/hugetlb.h>

  #include <linux/vmalloc.h>

  #include <linux/userfaultfd_k.h>

  #include <linux/elf.h>

  #include <linux/elf-randomize.h>
  #include <linux/personality.h>

  #include <linux/random.h>

  #include <linux/processor.h>
  #include <linux/sizes.h>
  #include <linux/compat.h>

  #include <linux/uaccess.h>

  #include "internal.h"

  /**
   * kfree_const - conditionally free memory
   * @x: pointer to the memory
   *
   * Function calls kfree only if @x is not in .rodata section.
   */
  void kfree_const(const void *x)
  {
  	if (!is_kernel_rodata((unsigned long)x))
  		kfree(x);
  }
  EXPORT_SYMBOL(kfree_const);

  /**

   * kstrdup - allocate space for and copy an existing string

   * @s: the string to duplicate
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory

   *
   * Return: newly allocated copy of @s or %NULL in case of error

   */
  char *kstrdup(const char *s, gfp_t gfp)
  {
  	size_t len;
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	len = strlen(s) + 1;

  	buf = kmalloc_track_caller(len, gfp);

  	if (buf)
  		memcpy(buf, s, len);
  	return buf;
  }
  EXPORT_SYMBOL(kstrdup);

  /**

   * kstrdup_const - conditionally duplicate an existing const string
   * @s: the string to duplicate
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory
   *

   * Note: Strings allocated by kstrdup_const should be freed by kfree_const and
   * must not be passed to krealloc().

   *
   * Return: source string if it is in .rodata section otherwise
   * fallback to kstrdup.

   */
  const char *kstrdup_const(const char *s, gfp_t gfp)
  {
  	if (is_kernel_rodata((unsigned long)s))
  		return s;
  
  	return kstrdup(s, gfp);
  }
  EXPORT_SYMBOL(kstrdup_const);
  
  /**

   * kstrndup - allocate space for and copy an existing string
   * @s: the string to duplicate
   * @max: read at most @max chars from @s
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory

   *
   * Note: Use kmemdup_nul() instead if the size is known exactly.

   *
   * Return: newly allocated copy of @s or %NULL in case of error

   */
  char *kstrndup(const char *s, size_t max, gfp_t gfp)
  {
  	size_t len;
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	len = strnlen(s, max);
  	buf = kmalloc_track_caller(len+1, gfp);
  	if (buf) {
  		memcpy(buf, s, len);
  		buf[len] = '\0';
  	}
  	return buf;
  }
  EXPORT_SYMBOL(kstrndup);
  
  /**

   * kmemdup - duplicate region of memory
   *
   * @src: memory region to duplicate
   * @len: memory region length
   * @gfp: GFP mask to use

   *
   * Return: newly allocated copy of @src or %NULL in case of error

   */
  void *kmemdup(const void *src, size_t len, gfp_t gfp)
  {
  	void *p;

  	p = kmalloc_track_caller(len, gfp);

  	if (p)
  		memcpy(p, src, len);
  	return p;
  }
  EXPORT_SYMBOL(kmemdup);

  /**

   * kmemdup_nul - Create a NUL-terminated string from unterminated data
   * @s: The data to stringify
   * @len: The size of the data
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory

   *
   * Return: newly allocated copy of @s with NUL-termination or %NULL in
   * case of error

   */
  char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
  {
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	buf = kmalloc_track_caller(len + 1, gfp);
  	if (buf) {
  		memcpy(buf, s, len);
  		buf[len] = '\0';
  	}
  	return buf;
  }
  EXPORT_SYMBOL(kmemdup_nul);
  
  /**

   * memdup_user - duplicate memory region from user space
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *

   * Return: an ERR_PTR() on failure.  Result is physically

   * contiguous, to be freed by kfree().

   */
  void *memdup_user(const void __user *src, size_t len)
  {
  	void *p;

  	p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);

  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  
  	return p;
  }
  EXPORT_SYMBOL(memdup_user);

  /**
   * vmemdup_user - duplicate memory region from user space
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *

   * Return: an ERR_PTR() on failure.  Result may be not

   * physically contiguous.  Use kvfree() to free.
   */
  void *vmemdup_user(const void __user *src, size_t len)
  {
  	void *p;
  
  	p = kvmalloc(len, GFP_USER);
  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kvfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  
  	return p;
  }
  EXPORT_SYMBOL(vmemdup_user);

  /**

   * strndup_user - duplicate an existing string from user space

   * @s: The string to duplicate
   * @n: Maximum number of bytes to copy, including the trailing NUL.

   *

   * Return: newly allocated copy of @s or an ERR_PTR() in case of error

   */
  char *strndup_user(const char __user *s, long n)
  {
  	char *p;
  	long length;
  
  	length = strnlen_user(s, n);
  
  	if (!length)
  		return ERR_PTR(-EFAULT);
  
  	if (length > n)
  		return ERR_PTR(-EINVAL);

  	p = memdup_user(s, length);

  	if (IS_ERR(p))
  		return p;

  
  	p[length - 1] = '\0';
  
  	return p;
  }
  EXPORT_SYMBOL(strndup_user);

  /**
   * memdup_user_nul - duplicate memory region from user space and NUL-terminate
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *

   * Return: an ERR_PTR() on failure.

   */
  void *memdup_user_nul(const void __user *src, size_t len)
  {
  	char *p;
  
  	/*
  	 * Always use GFP_KERNEL, since copy_from_user() can sleep and
  	 * cause pagefault, which makes it pointless to use GFP_NOFS
  	 * or GFP_ATOMIC.
  	 */
  	p = kmalloc_track_caller(len + 1, GFP_KERNEL);
  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  	p[len] = '\0';
  
  	return p;
  }
  EXPORT_SYMBOL(memdup_user_nul);

  void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,

  		struct vm_area_struct *prev)

  {
  	struct vm_area_struct *next;
  
  	vma->vm_prev = prev;
  	if (prev) {
  		next = prev->vm_next;
  		prev->vm_next = vma;
  	} else {

  		next = mm->mmap;

  		mm->mmap = vma;

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

  void __vma_unlink_list(struct mm_struct *mm, struct vm_area_struct *vma)
  {
  	struct vm_area_struct *prev, *next;
  
  	next = vma->vm_next;
  	prev = vma->vm_prev;
  	if (prev)
  		prev->vm_next = next;
  	else
  		mm->mmap = next;
  	if (next)
  		next->vm_prev = prev;
  }

  /* Check if the vma is being used as a stack by this task */

  int vma_is_stack_for_current(struct vm_area_struct *vma)

  {

  	struct task_struct * __maybe_unused t = current;

  	return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t));
  }

  #ifndef STACK_RND_MASK
  #define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))     /* 8MB of VA */
  #endif
  
  unsigned long randomize_stack_top(unsigned long stack_top)
  {
  	unsigned long random_variable = 0;
  
  	if (current->flags & PF_RANDOMIZE) {
  		random_variable = get_random_long();
  		random_variable &= STACK_RND_MASK;
  		random_variable <<= PAGE_SHIFT;
  	}
  #ifdef CONFIG_STACK_GROWSUP
  	return PAGE_ALIGN(stack_top) + random_variable;
  #else
  	return PAGE_ALIGN(stack_top) - random_variable;
  #endif
  }

  #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT

  unsigned long arch_randomize_brk(struct mm_struct *mm)
  {
  	/* Is the current task 32bit ? */
  	if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
  		return randomize_page(mm->brk, SZ_32M);
  
  	return randomize_page(mm->brk, SZ_1G);
  }

  unsigned long arch_mmap_rnd(void)
  {
  	unsigned long rnd;
  
  #ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
  	if (is_compat_task())
  		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
  	else
  #endif /* CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS */
  		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  
  	return rnd << PAGE_SHIFT;
  }

  
  static int mmap_is_legacy(struct rlimit *rlim_stack)
  {
  	if (current->personality & ADDR_COMPAT_LAYOUT)
  		return 1;
  
  	if (rlim_stack->rlim_cur == RLIM_INFINITY)
  		return 1;
  
  	return sysctl_legacy_va_layout;
  }
  
  /*
   * Leave enough space between the mmap area and the stack to honour ulimit in
   * the face of randomisation.
   */
  #define MIN_GAP		(SZ_128M)
  #define MAX_GAP		(STACK_TOP / 6 * 5)
  
  static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
  {
  	unsigned long gap = rlim_stack->rlim_cur;
  	unsigned long pad = stack_guard_gap;
  
  	/* Account for stack randomization if necessary */
  	if (current->flags & PF_RANDOMIZE)
  		pad += (STACK_RND_MASK << PAGE_SHIFT);
  
  	/* Values close to RLIM_INFINITY can overflow. */
  	if (gap + pad > gap)
  		gap += pad;
  
  	if (gap < MIN_GAP)
  		gap = MIN_GAP;
  	else if (gap > MAX_GAP)
  		gap = MAX_GAP;
  
  	return PAGE_ALIGN(STACK_TOP - gap - rnd);
  }
  
  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
  {
  	unsigned long random_factor = 0UL;
  
  	if (current->flags & PF_RANDOMIZE)
  		random_factor = arch_mmap_rnd();
  
  	if (mmap_is_legacy(rlim_stack)) {
  		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
  		mm->get_unmapped_area = arch_get_unmapped_area;
  	} else {
  		mm->mmap_base = mmap_base(random_factor, rlim_stack);
  		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  	}
  }
  #elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)

  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)

  {
  	mm->mmap_base = TASK_UNMAPPED_BASE;
  	mm->get_unmapped_area = arch_get_unmapped_area;

  }
  #endif

  /**
   * __account_locked_vm - account locked pages to an mm's locked_vm
   * @mm:          mm to account against
   * @pages:       number of pages to account
   * @inc:         %true if @pages should be considered positive, %false if not
   * @task:        task used to check RLIMIT_MEMLOCK
   * @bypass_rlim: %true if checking RLIMIT_MEMLOCK should be skipped
   *
   * Assumes @task and @mm are valid (i.e. at least one reference on each), and

   * that mmap_lock is held as writer.

   *
   * Return:
   * * 0       on success
   * * -ENOMEM if RLIMIT_MEMLOCK would be exceeded.
   */
  int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
  			struct task_struct *task, bool bypass_rlim)
  {
  	unsigned long locked_vm, limit;
  	int ret = 0;

  	mmap_assert_write_locked(mm);

  
  	locked_vm = mm->locked_vm;
  	if (inc) {
  		if (!bypass_rlim) {
  			limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
  			if (locked_vm + pages > limit)
  				ret = -ENOMEM;
  		}
  		if (!ret)
  			mm->locked_vm = locked_vm + pages;
  	} else {
  		WARN_ON_ONCE(pages > locked_vm);
  		mm->locked_vm = locked_vm - pages;
  	}
  
  	pr_debug("%s: [%d] caller %ps %c%lu %lu/%lu%s
  ", __func__, task->pid,
  		 (void *)_RET_IP_, (inc) ? '+' : '-', pages << PAGE_SHIFT,
  		 locked_vm << PAGE_SHIFT, task_rlimit(task, RLIMIT_MEMLOCK),
  		 ret ? " - exceeded" : "");
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(__account_locked_vm);
  
  /**
   * account_locked_vm - account locked pages to an mm's locked_vm
   * @mm:          mm to account against, may be NULL
   * @pages:       number of pages to account
   * @inc:         %true if @pages should be considered positive, %false if not
   *
   * Assumes a non-NULL @mm is valid (i.e. at least one reference on it).
   *
   * Return:
   * * 0       on success, or if mm is NULL
   * * -ENOMEM if RLIMIT_MEMLOCK would be exceeded.
   */
  int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc)
  {
  	int ret;
  
  	if (pages == 0 || !mm)
  		return 0;

  	mmap_write_lock(mm);

  	ret = __account_locked_vm(mm, pages, inc, current,
  				  capable(CAP_IPC_LOCK));

  	mmap_write_unlock(mm);

  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(account_locked_vm);

  unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
  	unsigned long len, unsigned long prot,

  	unsigned long flag, unsigned long pgoff)

  {
  	unsigned long ret;
  	struct mm_struct *mm = current->mm;

  	unsigned long populate;

  	LIST_HEAD(uf);

  
  	ret = security_mmap_file(file, prot, flag);
  	if (!ret) {

  		if (mmap_write_lock_killable(mm))

  			return -EINTR;

  		ret = do_mmap(file, addr, len, prot, flag, pgoff, &populate,
  			      &uf);

  		mmap_write_unlock(mm);

  		userfaultfd_unmap_complete(mm, &uf);

  		if (populate)
  			mm_populate(ret, populate);

  	}
  	return ret;
  }
  
  unsigned long vm_mmap(struct file *file, unsigned long addr,
  	unsigned long len, unsigned long prot,
  	unsigned long flag, unsigned long offset)
  {
  	if (unlikely(offset + PAGE_ALIGN(len) < offset))
  		return -EINVAL;

  	if (unlikely(offset_in_page(offset)))

  		return -EINVAL;

  	return vm_mmap_pgoff(file, addr, len, prot, flag, offset >> PAGE_SHIFT);

  }
  EXPORT_SYMBOL(vm_mmap);

  /**
   * kvmalloc_node - attempt to allocate physically contiguous memory, but upon
   * failure, fall back to non-contiguous (vmalloc) allocation.
   * @size: size of the request.
   * @flags: gfp mask for the allocation - must be compatible (superset) with GFP_KERNEL.
   * @node: numa node to allocate from
   *
   * Uses kmalloc to get the memory but if the allocation fails then falls back
   * to the vmalloc allocator. Use kvfree for freeing the memory.
   *

   * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported.
   * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is
   * preferable to the vmalloc fallback, due to visible performance drawbacks.

   *

   * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not
   * fall back to vmalloc.

   *
   * Return: pointer to the allocated memory of %NULL in case of failure

   */
  void *kvmalloc_node(size_t size, gfp_t flags, int node)
  {
  	gfp_t kmalloc_flags = flags;
  	void *ret;
  
  	/*
  	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
  	 * so the given set of flags has to be compatible.
  	 */

  	if ((flags & GFP_KERNEL) != GFP_KERNEL)
  		return kmalloc_node(size, flags, node);

  
  	/*

  	 * We want to attempt a large physically contiguous block first because
  	 * it is less likely to fragment multiple larger blocks and therefore
  	 * contribute to a long term fragmentation less than vmalloc fallback.
  	 * However make sure that larger requests are not too disruptive - no
  	 * OOM killer and no allocation failure warnings as we have a fallback.

  	 */

  	if (size > PAGE_SIZE) {
  		kmalloc_flags |= __GFP_NOWARN;

  		if (!(kmalloc_flags & __GFP_RETRY_MAYFAIL))

  			kmalloc_flags |= __GFP_NORETRY;
  	}

  
  	ret = kmalloc_node(size, kmalloc_flags, node);
  
  	/*
  	 * It doesn't really make sense to fallback to vmalloc for sub page
  	 * requests
  	 */
  	if (ret || size <= PAGE_SIZE)
  		return ret;

  	return __vmalloc_node(size, 1, flags, node,

  			__builtin_return_address(0));

  }
  EXPORT_SYMBOL(kvmalloc_node);

  /**

   * kvfree() - Free memory.
   * @addr: Pointer to allocated memory.

   *

   * kvfree frees memory allocated by any of vmalloc(), kmalloc() or kvmalloc().
   * It is slightly more efficient to use kfree() or vfree() if you are certain
   * that you know which one to use.
   *

   * Context: Either preemptible task context or not-NMI interrupt.

   */

  void kvfree(const void *addr)
  {
  	if (is_vmalloc_addr(addr))
  		vfree(addr);
  	else
  		kfree(addr);
  }
  EXPORT_SYMBOL(kvfree);

  /**
   * kvfree_sensitive - Free a data object containing sensitive information.
   * @addr: address of the data object to be freed.
   * @len: length of the data object.
   *
   * Use the special memzero_explicit() function to clear the content of a
   * kvmalloc'ed object containing sensitive data to make sure that the
   * compiler won't optimize out the data clearing.
   */
  void kvfree_sensitive(const void *addr, size_t len)
  {
  	if (likely(!ZERO_OR_NULL_PTR(addr))) {
  		memzero_explicit((void *)addr, len);
  		kvfree(addr);
  	}
  }
  EXPORT_SYMBOL(kvfree_sensitive);

  static inline void *__page_rmapping(struct page *page)
  {
  	unsigned long mapping;
  
  	mapping = (unsigned long)page->mapping;
  	mapping &= ~PAGE_MAPPING_FLAGS;
  
  	return (void *)mapping;
  }
  
  /* Neutral page->mapping pointer to address_space or anon_vma or other */
  void *page_rmapping(struct page *page)
  {
  	page = compound_head(page);
  	return __page_rmapping(page);
  }

  /*
   * Return true if this page is mapped into pagetables.
   * For compound page it returns true if any subpage of compound page is mapped.
   */
  bool page_mapped(struct page *page)
  {
  	int i;
  
  	if (likely(!PageCompound(page)))
  		return atomic_read(&page->_mapcount) >= 0;
  	page = compound_head(page);
  	if (atomic_read(compound_mapcount_ptr(page)) >= 0)
  		return true;
  	if (PageHuge(page))
  		return false;

  	for (i = 0; i < compound_nr(page); i++) {

  		if (atomic_read(&page[i]._mapcount) >= 0)
  			return true;
  	}
  	return false;
  }
  EXPORT_SYMBOL(page_mapped);

  struct anon_vma *page_anon_vma(struct page *page)
  {
  	unsigned long mapping;
  
  	page = compound_head(page);
  	mapping = (unsigned long)page->mapping;
  	if ((mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
  		return NULL;
  	return __page_rmapping(page);
  }

  struct address_space *page_mapping(struct page *page)
  {

  	struct address_space *mapping;
  
  	page = compound_head(page);

  	/* This happens if someone calls flush_dcache_page on slab page */
  	if (unlikely(PageSlab(page)))
  		return NULL;

  	if (unlikely(PageSwapCache(page))) {
  		swp_entry_t entry;
  
  		entry.val = page_private(page);

  		return swap_address_space(entry);
  	}

  	mapping = page->mapping;

  	if ((unsigned long)mapping & PAGE_MAPPING_ANON)

  		return NULL;

  
  	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);

  }

  EXPORT_SYMBOL(page_mapping);

  /*
   * For file cache pages, return the address_space, otherwise return NULL
   */
  struct address_space *page_mapping_file(struct page *page)
  {
  	if (unlikely(PageSwapCache(page)))
  		return NULL;
  	return page_mapping(page);
  }

  /* Slow path of page_mapcount() for compound pages */
  int __page_mapcount(struct page *page)
  {
  	int ret;
  
  	ret = atomic_read(&page->_mapcount) + 1;

  	/*
  	 * For file THP page->_mapcount contains total number of mapping
  	 * of the page: no need to look into compound_mapcount.
  	 */
  	if (!PageAnon(page) && !PageHuge(page))
  		return ret;

  	page = compound_head(page);
  	ret += atomic_read(compound_mapcount_ptr(page)) + 1;
  	if (PageDoubleMap(page))
  		ret--;
  	return ret;
  }
  EXPORT_SYMBOL_GPL(__page_mapcount);

  int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
  int sysctl_overcommit_ratio __read_mostly = 50;
  unsigned long sysctl_overcommit_kbytes __read_mostly;
  int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
  unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
  unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */

  int overcommit_ratio_handler(struct ctl_table *table, int write, void *buffer,
  		size_t *lenp, loff_t *ppos)

  {
  	int ret;
  
  	ret = proc_dointvec(table, write, buffer, lenp, ppos);
  	if (ret == 0 && write)
  		sysctl_overcommit_kbytes = 0;
  	return ret;
  }

  static void sync_overcommit_as(struct work_struct *dummy)
  {
  	percpu_counter_sync(&vm_committed_as);
  }
  
  int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
  		size_t *lenp, loff_t *ppos)
  {
  	struct ctl_table t;
  	int new_policy;
  	int ret;
  
  	/*
  	 * The deviation of sync_overcommit_as could be big with loose policy
  	 * like OVERCOMMIT_ALWAYS/OVERCOMMIT_GUESS. When changing policy to
  	 * strict OVERCOMMIT_NEVER, we need to reduce the deviation to comply
  	 * with the strict "NEVER", and to avoid possible race condtion (even
  	 * though user usually won't too frequently do the switching to policy
  	 * OVERCOMMIT_NEVER), the switch is done in the following order:
  	 *	1. changing the batch
  	 *	2. sync percpu count on each CPU
  	 *	3. switch the policy
  	 */
  	if (write) {
  		t = *table;
  		t.data = &new_policy;
  		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
  		if (ret)
  			return ret;
  
  		mm_compute_batch(new_policy);
  		if (new_policy == OVERCOMMIT_NEVER)
  			schedule_on_each_cpu(sync_overcommit_as);
  		sysctl_overcommit_memory = new_policy;
  	} else {
  		ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
  	}
  
  	return ret;
  }

  int overcommit_kbytes_handler(struct ctl_table *table, int write, void *buffer,
  		size_t *lenp, loff_t *ppos)

  {
  	int ret;
  
  	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  	if (ret == 0 && write)
  		sysctl_overcommit_ratio = 0;
  	return ret;
  }

  /*
   * Committed memory limit enforced when OVERCOMMIT_NEVER policy is used
   */
  unsigned long vm_commit_limit(void)
  {

  	unsigned long allowed;
  
  	if (sysctl_overcommit_kbytes)
  		allowed = sysctl_overcommit_kbytes >> (PAGE_SHIFT - 10);
  	else

  		allowed = ((totalram_pages() - hugetlb_total_pages())

  			   * sysctl_overcommit_ratio / 100);
  	allowed += total_swap_pages;
  
  	return allowed;

  }

  /*
   * Make sure vm_committed_as in one cacheline and not cacheline shared with
   * other variables. It can be updated by several CPUs frequently.
   */
  struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
  
  /*
   * The global memory commitment made in the system can be a metric
   * that can be used to drive ballooning decisions when Linux is hosted
   * as a guest. On Hyper-V, the host implements a policy engine for dynamically
   * balancing memory across competing virtual machines that are hosted.
   * Several metrics drive this policy engine including the guest reported
   * memory commitment.

   *
   * The time cost of this is very low for small platforms, and for big
   * platform like a 2S/36C/72T Skylake server, in worst case where
   * vm_committed_as's spinlock is under severe contention, the time cost
   * could be about 30~40 microseconds.

   */
  unsigned long vm_memory_committed(void)
  {

  	return percpu_counter_sum_positive(&vm_committed_as);

  }
  EXPORT_SYMBOL_GPL(vm_memory_committed);
  
  /*
   * Check that a process has enough memory to allocate a new virtual
   * mapping. 0 means there is enough memory for the allocation to
   * succeed and -ENOMEM implies there is not.
   *
   * We currently support three overcommit policies, which are set via the

   * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting.rst

   *
   * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
   * Additional code 2002 Jul 20 by Robert Love.
   *
   * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
   *
   * Note this is a helper function intended to be used by LSMs which
   * wish to use this logic.
   */
  int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
  {

  	long allowed;

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

  		if (pages > totalram_pages() + total_swap_pages)

  			goto error;

  		return 0;

  	}
  
  	allowed = vm_commit_limit();
  	/*
  	 * Reserve some for root
  	 */
  	if (!cap_sys_admin)
  		allowed -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
  
  	/*
  	 * Don't let a single process grow so big a user can't recover
  	 */
  	if (mm) {

  		long reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);

  		allowed -= min_t(long, mm->total_vm / 32, reserve);
  	}
  
  	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
  		return 0;
  error:
  	vm_unacct_memory(pages);
  
  	return -ENOMEM;
  }

  /**
   * get_cmdline() - copy the cmdline value to a buffer.
   * @task:     the task whose cmdline value to copy.
   * @buffer:   the buffer to copy to.
   * @buflen:   the length of the buffer. Larger cmdline values are truncated
   *            to this length.

   *
   * Return: the size of the cmdline field copied. Note that the copy does

   * not guarantee an ending NULL byte.
   */
  int get_cmdline(struct task_struct *task, char *buffer, int buflen)
  {
  	int res = 0;
  	unsigned int len;
  	struct mm_struct *mm = get_task_mm(task);

  	unsigned long arg_start, arg_end, env_start, env_end;

  	if (!mm)
  		goto out;
  	if (!mm->arg_end)
  		goto out_mm;	/* Shh! No looking before we're done */

  	spin_lock(&mm->arg_lock);

  	arg_start = mm->arg_start;
  	arg_end = mm->arg_end;
  	env_start = mm->env_start;
  	env_end = mm->env_end;

  	spin_unlock(&mm->arg_lock);

  
  	len = arg_end - arg_start;

  
  	if (len > buflen)
  		len = buflen;

  	res = access_process_vm(task, arg_start, buffer, len, FOLL_FORCE);

  
  	/*
  	 * If the nul at the end of args has been overwritten, then
  	 * assume application is using setproctitle(3).
  	 */
  	if (res > 0 && buffer[res-1] != '\0' && len < buflen) {
  		len = strnlen(buffer, res);
  		if (len < res) {
  			res = len;
  		} else {

  			len = env_end - env_start;

  			if (len > buflen - res)
  				len = buflen - res;

  			res += access_process_vm(task, env_start,

  						 buffer+res, len,
  						 FOLL_FORCE);

  			res = strnlen(buffer, res);
  		}
  	}
  out_mm:
  	mmput(mm);
  out:
  	return res;
  }

  int __weak memcmp_pages(struct page *page1, struct page *page2)

  {
  	char *addr1, *addr2;
  	int ret;
  
  	addr1 = kmap_atomic(page1);
  	addr2 = kmap_atomic(page2);
  	ret = memcmp(addr1, addr2, PAGE_SIZE);
  	kunmap_atomic(addr2);
  	kunmap_atomic(addr1);
  	return ret;
  }