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

  /*
   *  linux/mm/mmu_notifier.c
   *
   *  Copyright (C) 2008  Qumranet, Inc.
   *  Copyright (C) 2008  SGI

   *             Christoph Lameter <cl@linux.com>

   */
  
  #include <linux/rculist.h>
  #include <linux/mmu_notifier.h>

  #include <linux/export.h>

  #include <linux/mm.h>
  #include <linux/err.h>

  #include <linux/srcu.h>

  #include <linux/rcupdate.h>
  #include <linux/sched.h>

  #include <linux/sched/mm.h>

  #include <linux/slab.h>

  /* global SRCU for all MMs */

  DEFINE_STATIC_SRCU(srcu);

  #ifdef CONFIG_LOCKDEP
  struct lockdep_map __mmu_notifier_invalidate_range_start_map = {
  	.name = "mmu_notifier_invalidate_range_start"
  };
  #endif

  /*
   * This function can't run concurrently against mmu_notifier_register
   * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
   * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
   * in parallel despite there being no task using this mm any more,
   * through the vmas outside of the exit_mmap context, such as with
   * vmtruncate. This serializes against mmu_notifier_unregister with

   * the mmu_notifier_mm->lock in addition to SRCU and it serializes
   * against the other mmu notifiers with SRCU. struct mmu_notifier_mm

   * can't go away from under us as exit_mmap holds an mm_count pin
   * itself.
   */
  void __mmu_notifier_release(struct mm_struct *mm)
  {
  	struct mmu_notifier *mn;

  	int id;

  
  	/*

  	 * SRCU here will block mmu_notifier_unregister until
  	 * ->release returns.

  	 */

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
  		/*
  		 * If ->release runs before mmu_notifier_unregister it must be
  		 * handled, as it's the only way for the driver to flush all
  		 * existing sptes and stop the driver from establishing any more
  		 * sptes before all the pages in the mm are freed.
  		 */
  		if (mn->ops->release)
  			mn->ops->release(mn, mm);

  	spin_lock(&mm->mmu_notifier_mm->lock);
  	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
  		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
  				 struct mmu_notifier,
  				 hlist);
  		/*

  		 * We arrived before mmu_notifier_unregister so
  		 * mmu_notifier_unregister will do nothing other than to wait
  		 * for ->release to finish and for mmu_notifier_unregister to
  		 * return.

  		 */
  		hlist_del_init_rcu(&mn->hlist);

  	}
  	spin_unlock(&mm->mmu_notifier_mm->lock);

  	srcu_read_unlock(&srcu, id);

  
  	/*

  	 * synchronize_srcu here prevents mmu_notifier_release from returning to
  	 * exit_mmap (which would proceed with freeing all pages in the mm)
  	 * until the ->release method returns, if it was invoked by
  	 * mmu_notifier_unregister.
  	 *
  	 * The mmu_notifier_mm can't go away from under us because one mm_count
  	 * is held by exit_mmap.

  	 */

  	synchronize_srcu(&srcu);

  }
  
  /*
   * If no young bitflag is supported by the hardware, ->clear_flush_young can
   * unmap the address and return 1 or 0 depending if the mapping previously
   * existed or not.
   */
  int __mmu_notifier_clear_flush_young(struct mm_struct *mm,

  					unsigned long start,
  					unsigned long end)

  {
  	struct mmu_notifier *mn;

  	int young = 0, id;

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {

  		if (mn->ops->clear_flush_young)

  			young |= mn->ops->clear_flush_young(mn, mm, start, end);

  	}

  	srcu_read_unlock(&srcu, id);

  
  	return young;
  }

  int __mmu_notifier_clear_young(struct mm_struct *mm,
  			       unsigned long start,
  			       unsigned long end)
  {
  	struct mmu_notifier *mn;
  	int young = 0, id;
  
  	id = srcu_read_lock(&srcu);
  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
  		if (mn->ops->clear_young)
  			young |= mn->ops->clear_young(mn, mm, start, end);
  	}
  	srcu_read_unlock(&srcu, id);
  
  	return young;
  }

  int __mmu_notifier_test_young(struct mm_struct *mm,
  			      unsigned long address)
  {
  	struct mmu_notifier *mn;

  	int young = 0, id;

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {

  		if (mn->ops->test_young) {
  			young = mn->ops->test_young(mn, mm, address);
  			if (young)
  				break;
  		}
  	}

  	srcu_read_unlock(&srcu, id);

  
  	return young;
  }

  void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
  			       pte_t pte)
  {
  	struct mmu_notifier *mn;

  	int id;

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {

  		if (mn->ops->change_pte)
  			mn->ops->change_pte(mn, mm, address, pte);

  	}

  	srcu_read_unlock(&srcu, id);

  }

  int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)

  {
  	struct mmu_notifier *mn;

  	int ret = 0;

  	int id;

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {

  		if (mn->ops->invalidate_range_start) {

  			int _ret;
  
  			if (!mmu_notifier_range_blockable(range))
  				non_block_start();
  			_ret = mn->ops->invalidate_range_start(mn, range);
  			if (!mmu_notifier_range_blockable(range))
  				non_block_end();

  			if (_ret) {
  				pr_info("%pS callback failed with %d in %sblockable context.
  ",

  					mn->ops->invalidate_range_start, _ret,

  					!mmu_notifier_range_blockable(range) ? "non-" : "");

  				WARN_ON(mmu_notifier_range_blockable(range) ||

  					_ret != -EAGAIN);

  				ret = _ret;
  			}
  		}

  	}

  	srcu_read_unlock(&srcu, id);

  
  	return ret;

  }

  void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,

  					 bool only_end)

  {
  	struct mmu_notifier *mn;

  	int id;

  	lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);

  	id = srcu_read_lock(&srcu);

  	hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {

  		/*
  		 * Call invalidate_range here too to avoid the need for the
  		 * subsystem of having to register an invalidate_range_end
  		 * call-back when there is invalidate_range already. Usually a
  		 * subsystem registers either invalidate_range_start()/end() or
  		 * invalidate_range(), so this will be no additional overhead
  		 * (besides the pointer check).

  		 *
  		 * We skip call to invalidate_range() if we know it is safe ie
  		 * call site use mmu_notifier_invalidate_range_only_end() which
  		 * is safe to do when we know that a call to invalidate_range()
  		 * already happen under page table lock.

  		 */

  		if (!only_end && mn->ops->invalidate_range)

  			mn->ops->invalidate_range(mn, range->mm,
  						  range->start,
  						  range->end);

  		if (mn->ops->invalidate_range_end) {
  			if (!mmu_notifier_range_blockable(range))
  				non_block_start();

  			mn->ops->invalidate_range_end(mn, range);

  			if (!mmu_notifier_range_blockable(range))
  				non_block_end();
  		}

  	}

  	srcu_read_unlock(&srcu, id);

  	lock_map_release(&__mmu_notifier_invalidate_range_start_map);

  }

  void __mmu_notifier_invalidate_range(struct mm_struct *mm,
  				  unsigned long start, unsigned long end)
  {
  	struct mmu_notifier *mn;
  	int id;
  
  	id = srcu_read_lock(&srcu);
  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
  		if (mn->ops->invalidate_range)
  			mn->ops->invalidate_range(mn, mm, start, end);
  	}
  	srcu_read_unlock(&srcu, id);
  }

  /*
   * Same as mmu_notifier_register but here the caller must hold the
   * mmap_sem in write mode.
   */
  int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)

  {

  	struct mmu_notifier_mm *mmu_notifier_mm = NULL;

  	int ret;

  	lockdep_assert_held_write(&mm->mmap_sem);

  	BUG_ON(atomic_read(&mm->mm_users) <= 0);

  	if (IS_ENABLED(CONFIG_LOCKDEP)) {
  		fs_reclaim_acquire(GFP_KERNEL);
  		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
  		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
  		fs_reclaim_release(GFP_KERNEL);
  	}

  	mn->mm = mm;
  	mn->users = 1;

  	if (!mm->mmu_notifier_mm) {
  		/*
  		 * kmalloc cannot be called under mm_take_all_locks(), but we
  		 * know that mm->mmu_notifier_mm can't change while we hold
  		 * the write side of the mmap_sem.
  		 */
  		mmu_notifier_mm =
  			kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
  		if (!mmu_notifier_mm)
  			return -ENOMEM;
  
  		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
  		spin_lock_init(&mmu_notifier_mm->lock);
  	}

  	ret = mm_take_all_locks(mm);
  	if (unlikely(ret))

  		goto out_clean;

  	/* Pairs with the mmdrop in mmu_notifier_unregister_* */

  	mmgrab(mm);

  
  	/*
  	 * Serialize the update against mmu_notifier_unregister. A
  	 * side note: mmu_notifier_release can't run concurrently with
  	 * us because we hold the mm_users pin (either implicitly as
  	 * current->mm or explicitly with get_task_mm() or similar).
  	 * We can't race against any other mmu notifier method either
  	 * thanks to mm_take_all_locks().
  	 */

  	if (mmu_notifier_mm)
  		mm->mmu_notifier_mm = mmu_notifier_mm;

  	spin_lock(&mm->mmu_notifier_mm->lock);

  	hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list);

  	spin_unlock(&mm->mmu_notifier_mm->lock);
  
  	mm_drop_all_locks(mm);

  	BUG_ON(atomic_read(&mm->mm_users) <= 0);
  	return 0;

  out_clean:

  	kfree(mmu_notifier_mm);

  	return ret;
  }

  EXPORT_SYMBOL_GPL(__mmu_notifier_register);

  /**
   * mmu_notifier_register - Register a notifier on a mm
   * @mn: The notifier to attach
   * @mm: The mm to attach the notifier to
   *

   * Must not hold mmap_sem nor any other VM related lock when calling
   * this registration function. Must also ensure mm_users can't go down
   * to zero while this runs to avoid races with mmu_notifier_release,
   * so mm has to be current->mm or the mm should be pinned safely such
   * as with get_task_mm(). If the mm is not current->mm, the mm_users
   * pin should be released by calling mmput after mmu_notifier_register

   * returns.
   *
   * mmu_notifier_unregister() or mmu_notifier_put() must be always called to
   * unregister the notifier.
   *
   * While the caller has a mmu_notifier get the mn->mm pointer will remain
   * valid, and can be converted to an active mm pointer via mmget_not_zero().

   */
  int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
  {

  	int ret;

  	down_write(&mm->mmap_sem);
  	ret = __mmu_notifier_register(mn, mm);
  	up_write(&mm->mmap_sem);
  	return ret;

  }

  EXPORT_SYMBOL_GPL(mmu_notifier_register);

  static struct mmu_notifier *
  find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
  {
  	struct mmu_notifier *mn;
  
  	spin_lock(&mm->mmu_notifier_mm->lock);
  	hlist_for_each_entry_rcu (mn, &mm->mmu_notifier_mm->list, hlist) {
  		if (mn->ops != ops)
  			continue;
  
  		if (likely(mn->users != UINT_MAX))
  			mn->users++;
  		else
  			mn = ERR_PTR(-EOVERFLOW);
  		spin_unlock(&mm->mmu_notifier_mm->lock);
  		return mn;
  	}
  	spin_unlock(&mm->mmu_notifier_mm->lock);
  	return NULL;
  }
  
  /**
   * mmu_notifier_get_locked - Return the single struct mmu_notifier for
   *                           the mm & ops
   * @ops: The operations struct being subscribe with
   * @mm : The mm to attach notifiers too
   *
   * This function either allocates a new mmu_notifier via
   * ops->alloc_notifier(), or returns an already existing notifier on the
   * list. The value of the ops pointer is used to determine when two notifiers
   * are the same.
   *
   * Each call to mmu_notifier_get() must be paired with a call to
   * mmu_notifier_put(). The caller must hold the write side of mm->mmap_sem.
   *
   * While the caller has a mmu_notifier get the mm pointer will remain valid,
   * and can be converted to an active mm pointer via mmget_not_zero().
   */
  struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
  					     struct mm_struct *mm)
  {
  	struct mmu_notifier *mn;
  	int ret;
  
  	lockdep_assert_held_write(&mm->mmap_sem);
  
  	if (mm->mmu_notifier_mm) {
  		mn = find_get_mmu_notifier(mm, ops);
  		if (mn)
  			return mn;
  	}
  
  	mn = ops->alloc_notifier(mm);
  	if (IS_ERR(mn))
  		return mn;
  	mn->ops = ops;
  	ret = __mmu_notifier_register(mn, mm);
  	if (ret)
  		goto out_free;
  	return mn;
  out_free:
  	mn->ops->free_notifier(mn);
  	return ERR_PTR(ret);
  }
  EXPORT_SYMBOL_GPL(mmu_notifier_get_locked);

  /* this is called after the last mmu_notifier_unregister() returned */
  void __mmu_notifier_mm_destroy(struct mm_struct *mm)
  {
  	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
  	kfree(mm->mmu_notifier_mm);
  	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
  }
  
  /*
   * This releases the mm_count pin automatically and frees the mm
   * structure if it was the last user of it. It serializes against

   * running mmu notifiers with SRCU and against mmu_notifier_unregister
   * with the unregister lock + SRCU. All sptes must be dropped before

   * calling mmu_notifier_unregister. ->release or any other notifier
   * method may be invoked concurrently with mmu_notifier_unregister,
   * and only after mmu_notifier_unregister returned we're guaranteed
   * that ->release or any other method can't run anymore.
   */
  void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
  {
  	BUG_ON(atomic_read(&mm->mm_count) <= 0);

  	if (!hlist_unhashed(&mn->hlist)) {

  		/*
  		 * SRCU here will force exit_mmap to wait for ->release to
  		 * finish before freeing the pages.
  		 */

  		int id;

  		id = srcu_read_lock(&srcu);

  		/*

  		 * exit_mmap will block in mmu_notifier_release to guarantee
  		 * that ->release is called before freeing the pages.

  		 */
  		if (mn->ops->release)
  			mn->ops->release(mn, mm);

  		srcu_read_unlock(&srcu, id);

  		spin_lock(&mm->mmu_notifier_mm->lock);

  		/*

  		 * Can not use list_del_rcu() since __mmu_notifier_release
  		 * can delete it before we hold the lock.

  		 */

  		hlist_del_init_rcu(&mn->hlist);

  		spin_unlock(&mm->mmu_notifier_mm->lock);

  	}

  
  	/*

  	 * Wait for any running method to finish, of course including

  	 * ->release if it was run by mmu_notifier_release instead of us.

  	 */

  	synchronize_srcu(&srcu);

  
  	BUG_ON(atomic_read(&mm->mm_count) <= 0);
  
  	mmdrop(mm);
  }
  EXPORT_SYMBOL_GPL(mmu_notifier_unregister);

  static void mmu_notifier_free_rcu(struct rcu_head *rcu)
  {
  	struct mmu_notifier *mn = container_of(rcu, struct mmu_notifier, rcu);
  	struct mm_struct *mm = mn->mm;
  
  	mn->ops->free_notifier(mn);
  	/* Pairs with the get in __mmu_notifier_register() */
  	mmdrop(mm);
  }
  
  /**
   * mmu_notifier_put - Release the reference on the notifier
   * @mn: The notifier to act on
   *
   * This function must be paired with each mmu_notifier_get(), it releases the
   * reference obtained by the get. If this is the last reference then process
   * to free the notifier will be run asynchronously.
   *
   * Unlike mmu_notifier_unregister() the get/put flow only calls ops->release
   * when the mm_struct is destroyed. Instead free_notifier is always called to
   * release any resources held by the user.
   *
   * As ops->release is not guaranteed to be called, the user must ensure that
   * all sptes are dropped, and no new sptes can be established before
   * mmu_notifier_put() is called.
   *
   * This function can be called from the ops->release callback, however the
   * caller must still ensure it is called pairwise with mmu_notifier_get().
   *
   * Modules calling this function must call mmu_notifier_synchronize() in
   * their __exit functions to ensure the async work is completed.
   */
  void mmu_notifier_put(struct mmu_notifier *mn)
  {
  	struct mm_struct *mm = mn->mm;
  
  	spin_lock(&mm->mmu_notifier_mm->lock);
  	if (WARN_ON(!mn->users) || --mn->users)
  		goto out_unlock;
  	hlist_del_init_rcu(&mn->hlist);
  	spin_unlock(&mm->mmu_notifier_mm->lock);
  
  	call_srcu(&srcu, &mn->rcu, mmu_notifier_free_rcu);
  	return;
  
  out_unlock:
  	spin_unlock(&mm->mmu_notifier_mm->lock);
  }
  EXPORT_SYMBOL_GPL(mmu_notifier_put);
  
  /**
   * mmu_notifier_synchronize - Ensure all mmu_notifiers are freed
   *
   * This function ensures that all outstanding async SRU work from
   * mmu_notifier_put() is completed. After it returns any mmu_notifier_ops
   * associated with an unused mmu_notifier will no longer be called.
   *
   * Before using the caller must ensure that all of its mmu_notifiers have been
   * fully released via mmu_notifier_put().
   *
   * Modules using the mmu_notifier_put() API should call this in their __exit
   * function to avoid module unloading races.
   */
  void mmu_notifier_synchronize(void)
  {
  	synchronize_srcu(&srcu);
  }
  EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);

  bool
  mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range)
  {
  	if (!range->vma || range->event != MMU_NOTIFY_PROTECTION_VMA)
  		return false;
  	/* Return true if the vma still have the read flag set. */
  	return range->vma->vm_flags & VM_READ;
  }
  EXPORT_SYMBOL_GPL(mmu_notifier_range_update_to_read_only);