diff options
Diffstat (limited to 'mm/mmu_notifier.c')
| -rw-r--r-- | mm/mmu_notifier.c | 1132 |
1 files changed, 1132 insertions, 0 deletions
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c new file mode 100644 index 000000000..f45ff1b76 --- /dev/null +++ b/mm/mmu_notifier.c @@ -0,0 +1,1132 @@ +// 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/interval_tree.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 + +/* + * The mmu_notifier_subscriptions structure is allocated and installed in + * mm->notifier_subscriptions inside the mm_take_all_locks() protected + * critical section and it's released only when mm_count reaches zero + * in mmdrop(). + */ +struct mmu_notifier_subscriptions { + /* all mmu notifiers registered in this mm are queued in this list */ + struct hlist_head list; + bool has_itree; + /* to serialize the list modifications and hlist_unhashed */ + spinlock_t lock; + unsigned long invalidate_seq; + unsigned long active_invalidate_ranges; + struct rb_root_cached itree; + wait_queue_head_t wq; + struct hlist_head deferred_list; +}; + +/* + * This is a collision-retry read-side/write-side 'lock', a lot like a + * seqcount, however this allows multiple write-sides to hold it at + * once. Conceptually the write side is protecting the values of the PTEs in + * this mm, such that PTES cannot be read into SPTEs (shadow PTEs) while any + * writer exists. + * + * Note that the core mm creates nested invalidate_range_start()/end() regions + * within the same thread, and runs invalidate_range_start()/end() in parallel + * on multiple CPUs. This is designed to not reduce concurrency or block + * progress on the mm side. + * + * As a secondary function, holding the full write side also serves to prevent + * writers for the itree, this is an optimization to avoid extra locking + * during invalidate_range_start/end notifiers. + * + * The write side has two states, fully excluded: + * - mm->active_invalidate_ranges != 0 + * - subscriptions->invalidate_seq & 1 == True (odd) + * - some range on the mm_struct is being invalidated + * - the itree is not allowed to change + * + * And partially excluded: + * - mm->active_invalidate_ranges != 0 + * - subscriptions->invalidate_seq & 1 == False (even) + * - some range on the mm_struct is being invalidated + * - the itree is allowed to change + * + * Operations on notifier_subscriptions->invalidate_seq (under spinlock): + * seq |= 1 # Begin writing + * seq++ # Release the writing state + * seq & 1 # True if a writer exists + * + * The later state avoids some expensive work on inv_end in the common case of + * no mmu_interval_notifier monitoring the VA. + */ +static bool +mn_itree_is_invalidating(struct mmu_notifier_subscriptions *subscriptions) +{ + lockdep_assert_held(&subscriptions->lock); + return subscriptions->invalidate_seq & 1; +} + +static struct mmu_interval_notifier * +mn_itree_inv_start_range(struct mmu_notifier_subscriptions *subscriptions, + const struct mmu_notifier_range *range, + unsigned long *seq) +{ + struct interval_tree_node *node; + struct mmu_interval_notifier *res = NULL; + + spin_lock(&subscriptions->lock); + subscriptions->active_invalidate_ranges++; + node = interval_tree_iter_first(&subscriptions->itree, range->start, + range->end - 1); + if (node) { + subscriptions->invalidate_seq |= 1; + res = container_of(node, struct mmu_interval_notifier, + interval_tree); + } + + *seq = subscriptions->invalidate_seq; + spin_unlock(&subscriptions->lock); + return res; +} + +static struct mmu_interval_notifier * +mn_itree_inv_next(struct mmu_interval_notifier *interval_sub, + const struct mmu_notifier_range *range) +{ + struct interval_tree_node *node; + + node = interval_tree_iter_next(&interval_sub->interval_tree, + range->start, range->end - 1); + if (!node) + return NULL; + return container_of(node, struct mmu_interval_notifier, interval_tree); +} + +static void mn_itree_inv_end(struct mmu_notifier_subscriptions *subscriptions) +{ + struct mmu_interval_notifier *interval_sub; + struct hlist_node *next; + + spin_lock(&subscriptions->lock); + if (--subscriptions->active_invalidate_ranges || + !mn_itree_is_invalidating(subscriptions)) { + spin_unlock(&subscriptions->lock); + return; + } + + /* Make invalidate_seq even */ + subscriptions->invalidate_seq++; + + /* + * The inv_end incorporates a deferred mechanism like rtnl_unlock(). + * Adds and removes are queued until the final inv_end happens then + * they are progressed. This arrangement for tree updates is used to + * avoid using a blocking lock during invalidate_range_start. + */ + hlist_for_each_entry_safe(interval_sub, next, + &subscriptions->deferred_list, + deferred_item) { + if (RB_EMPTY_NODE(&interval_sub->interval_tree.rb)) + interval_tree_insert(&interval_sub->interval_tree, + &subscriptions->itree); + else + interval_tree_remove(&interval_sub->interval_tree, + &subscriptions->itree); + hlist_del(&interval_sub->deferred_item); + } + spin_unlock(&subscriptions->lock); + + wake_up_all(&subscriptions->wq); +} + +/** + * mmu_interval_read_begin - Begin a read side critical section against a VA + * range + * @interval_sub: The interval subscription + * + * mmu_iterval_read_begin()/mmu_iterval_read_retry() implement a + * collision-retry scheme similar to seqcount for the VA range under + * subscription. If the mm invokes invalidation during the critical section + * then mmu_interval_read_retry() will return true. + * + * This is useful to obtain shadow PTEs where teardown or setup of the SPTEs + * require a blocking context. The critical region formed by this can sleep, + * and the required 'user_lock' can also be a sleeping lock. + * + * The caller is required to provide a 'user_lock' to serialize both teardown + * and setup. + * + * The return value should be passed to mmu_interval_read_retry(). + */ +unsigned long +mmu_interval_read_begin(struct mmu_interval_notifier *interval_sub) +{ + struct mmu_notifier_subscriptions *subscriptions = + interval_sub->mm->notifier_subscriptions; + unsigned long seq; + bool is_invalidating; + + /* + * If the subscription has a different seq value under the user_lock + * than we started with then it has collided. + * + * If the subscription currently has the same seq value as the + * subscriptions seq, then it is currently between + * invalidate_start/end and is colliding. + * + * The locking looks broadly like this: + * mn_tree_invalidate_start(): mmu_interval_read_begin(): + * spin_lock + * seq = READ_ONCE(interval_sub->invalidate_seq); + * seq == subs->invalidate_seq + * spin_unlock + * spin_lock + * seq = ++subscriptions->invalidate_seq + * spin_unlock + * op->invalidate_range(): + * user_lock + * mmu_interval_set_seq() + * interval_sub->invalidate_seq = seq + * user_unlock + * + * [Required: mmu_interval_read_retry() == true] + * + * mn_itree_inv_end(): + * spin_lock + * seq = ++subscriptions->invalidate_seq + * spin_unlock + * + * user_lock + * mmu_interval_read_retry(): + * interval_sub->invalidate_seq != seq + * user_unlock + * + * Barriers are not needed here as any races here are closed by an + * eventual mmu_interval_read_retry(), which provides a barrier via the + * user_lock. + */ + spin_lock(&subscriptions->lock); + /* Pairs with the WRITE_ONCE in mmu_interval_set_seq() */ + seq = READ_ONCE(interval_sub->invalidate_seq); + is_invalidating = seq == subscriptions->invalidate_seq; + spin_unlock(&subscriptions->lock); + + /* + * interval_sub->invalidate_seq must always be set to an odd value via + * mmu_interval_set_seq() using the provided cur_seq from + * mn_itree_inv_start_range(). This ensures that if seq does wrap we + * will always clear the below sleep in some reasonable time as + * subscriptions->invalidate_seq is even in the idle state. + */ + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); + lock_map_release(&__mmu_notifier_invalidate_range_start_map); + if (is_invalidating) + wait_event(subscriptions->wq, + READ_ONCE(subscriptions->invalidate_seq) != seq); + + /* + * Notice that mmu_interval_read_retry() can already be true at this + * point, avoiding loops here allows the caller to provide a global + * time bound. + */ + + return seq; +} +EXPORT_SYMBOL_GPL(mmu_interval_read_begin); + +static void mn_itree_release(struct mmu_notifier_subscriptions *subscriptions, + struct mm_struct *mm) +{ + struct mmu_notifier_range range = { + .flags = MMU_NOTIFIER_RANGE_BLOCKABLE, + .event = MMU_NOTIFY_RELEASE, + .mm = mm, + .start = 0, + .end = ULONG_MAX, + }; + struct mmu_interval_notifier *interval_sub; + unsigned long cur_seq; + bool ret; + + for (interval_sub = + mn_itree_inv_start_range(subscriptions, &range, &cur_seq); + interval_sub; + interval_sub = mn_itree_inv_next(interval_sub, &range)) { + ret = interval_sub->ops->invalidate(interval_sub, &range, + cur_seq); + WARN_ON(!ret); + } + + mn_itree_inv_end(subscriptions); +} + +/* + * 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 notifier_subscriptions->lock in addition to SRCU and it serializes + * against the other mmu notifiers with SRCU. struct mmu_notifier_subscriptions + * can't go away from under us as exit_mmap holds an mm_count pin + * itself. + */ +static void mn_hlist_release(struct mmu_notifier_subscriptions *subscriptions, + struct mm_struct *mm) +{ + struct mmu_notifier *subscription; + int id; + + /* + * SRCU here will block mmu_notifier_unregister until + * ->release returns. + */ + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) + /* + * 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 (subscription->ops->release) + subscription->ops->release(subscription, mm); + + spin_lock(&subscriptions->lock); + while (unlikely(!hlist_empty(&subscriptions->list))) { + subscription = hlist_entry(subscriptions->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(&subscription->hlist); + } + spin_unlock(&subscriptions->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 notifier_subscriptions can't go away from under us because + * one mm_count is held by exit_mmap. + */ + synchronize_srcu(&srcu); +} + +void __mmu_notifier_release(struct mm_struct *mm) +{ + struct mmu_notifier_subscriptions *subscriptions = + mm->notifier_subscriptions; + + if (subscriptions->has_itree) + mn_itree_release(subscriptions, mm); + + if (!hlist_empty(&subscriptions->list)) + mn_hlist_release(subscriptions, mm); +} + +/* + * 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 *subscription; + int young = 0, id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + if (subscription->ops->clear_flush_young) + young |= subscription->ops->clear_flush_young( + subscription, 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 *subscription; + int young = 0, id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + if (subscription->ops->clear_young) + young |= subscription->ops->clear_young(subscription, + 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 *subscription; + int young = 0, id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + if (subscription->ops->test_young) { + young = subscription->ops->test_young(subscription, 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 *subscription; + int id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + if (subscription->ops->change_pte) + subscription->ops->change_pte(subscription, mm, address, + pte); + } + srcu_read_unlock(&srcu, id); +} + +static int mn_itree_invalidate(struct mmu_notifier_subscriptions *subscriptions, + const struct mmu_notifier_range *range) +{ + struct mmu_interval_notifier *interval_sub; + unsigned long cur_seq; + + for (interval_sub = + mn_itree_inv_start_range(subscriptions, range, &cur_seq); + interval_sub; + interval_sub = mn_itree_inv_next(interval_sub, range)) { + bool ret; + + ret = interval_sub->ops->invalidate(interval_sub, range, + cur_seq); + if (!ret) { + if (WARN_ON(mmu_notifier_range_blockable(range))) + continue; + goto out_would_block; + } + } + return 0; + +out_would_block: + /* + * On -EAGAIN the non-blocking caller is not allowed to call + * invalidate_range_end() + */ + mn_itree_inv_end(subscriptions); + return -EAGAIN; +} + +static int mn_hlist_invalidate_range_start( + struct mmu_notifier_subscriptions *subscriptions, + struct mmu_notifier_range *range) +{ + struct mmu_notifier *subscription; + int ret = 0; + int id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + const struct mmu_notifier_ops *ops = subscription->ops; + + if (ops->invalidate_range_start) { + int _ret; + + if (!mmu_notifier_range_blockable(range)) + non_block_start(); + _ret = ops->invalidate_range_start(subscription, range); + if (!mmu_notifier_range_blockable(range)) + non_block_end(); + if (_ret) { + pr_info("%pS callback failed with %d in %sblockable context.\n", + ops->invalidate_range_start, _ret, + !mmu_notifier_range_blockable(range) ? + "non-" : + ""); + WARN_ON(mmu_notifier_range_blockable(range) || + _ret != -EAGAIN); + /* + * We call all the notifiers on any EAGAIN, + * there is no way for a notifier to know if + * its start method failed, thus a start that + * does EAGAIN can't also do end. + */ + WARN_ON(ops->invalidate_range_end); + ret = _ret; + } + } + } + + if (ret) { + /* + * Must be non-blocking to get here. If there are multiple + * notifiers and one or more failed start, any that succeeded + * start are expecting their end to be called. Do so now. + */ + hlist_for_each_entry_rcu(subscription, &subscriptions->list, + hlist, srcu_read_lock_held(&srcu)) { + if (!subscription->ops->invalidate_range_end) + continue; + + subscription->ops->invalidate_range_end(subscription, + range); + } + } + srcu_read_unlock(&srcu, id); + + return ret; +} + +int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range) +{ + struct mmu_notifier_subscriptions *subscriptions = + range->mm->notifier_subscriptions; + int ret; + + if (subscriptions->has_itree) { + ret = mn_itree_invalidate(subscriptions, range); + if (ret) + return ret; + } + if (!hlist_empty(&subscriptions->list)) + return mn_hlist_invalidate_range_start(subscriptions, range); + return 0; +} + +static void +mn_hlist_invalidate_end(struct mmu_notifier_subscriptions *subscriptions, + struct mmu_notifier_range *range, bool only_end) +{ + struct mmu_notifier *subscription; + int id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, &subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + /* + * 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 && subscription->ops->invalidate_range) + subscription->ops->invalidate_range(subscription, + range->mm, + range->start, + range->end); + if (subscription->ops->invalidate_range_end) { + if (!mmu_notifier_range_blockable(range)) + non_block_start(); + subscription->ops->invalidate_range_end(subscription, + range); + if (!mmu_notifier_range_blockable(range)) + non_block_end(); + } + } + srcu_read_unlock(&srcu, id); +} + +void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range, + bool only_end) +{ + struct mmu_notifier_subscriptions *subscriptions = + range->mm->notifier_subscriptions; + + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); + if (subscriptions->has_itree) + mn_itree_inv_end(subscriptions); + + if (!hlist_empty(&subscriptions->list)) + mn_hlist_invalidate_end(subscriptions, range, only_end); + 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 *subscription; + int id; + + id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + srcu_read_lock_held(&srcu)) { + if (subscription->ops->invalidate_range) + subscription->ops->invalidate_range(subscription, mm, + start, end); + } + srcu_read_unlock(&srcu, id); +} + +/* + * Same as mmu_notifier_register but here the caller must hold the mmap_lock in + * write mode. A NULL mn signals the notifier is being registered for itree + * mode. + */ +int __mmu_notifier_register(struct mmu_notifier *subscription, + struct mm_struct *mm) +{ + struct mmu_notifier_subscriptions *subscriptions = NULL; + int ret; + + mmap_assert_write_locked(mm); + BUG_ON(atomic_read(&mm->mm_users) <= 0); + + if (!mm->notifier_subscriptions) { + /* + * kmalloc cannot be called under mm_take_all_locks(), but we + * know that mm->notifier_subscriptions can't change while we + * hold the write side of the mmap_lock. + */ + subscriptions = kzalloc( + sizeof(struct mmu_notifier_subscriptions), GFP_KERNEL); + if (!subscriptions) + return -ENOMEM; + + INIT_HLIST_HEAD(&subscriptions->list); + spin_lock_init(&subscriptions->lock); + subscriptions->invalidate_seq = 2; + subscriptions->itree = RB_ROOT_CACHED; + init_waitqueue_head(&subscriptions->wq); + INIT_HLIST_HEAD(&subscriptions->deferred_list); + } + + ret = mm_take_all_locks(mm); + if (unlikely(ret)) + goto out_clean; + + /* + * 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(). + * + * release semantics on the initialization of the + * mmu_notifier_subscriptions's contents are provided for unlocked + * readers. acquire can only be used while holding the mmgrab or + * mmget, and is safe because once created the + * mmu_notifier_subscriptions is not freed until the mm is destroyed. + * As above, users holding the mmap_lock or one of the + * mm_take_all_locks() do not need to use acquire semantics. + */ + if (subscriptions) + smp_store_release(&mm->notifier_subscriptions, subscriptions); + + if (subscription) { + /* Pairs with the mmdrop in mmu_notifier_unregister_* */ + mmgrab(mm); + subscription->mm = mm; + subscription->users = 1; + + spin_lock(&mm->notifier_subscriptions->lock); + hlist_add_head_rcu(&subscription->hlist, + &mm->notifier_subscriptions->list); + spin_unlock(&mm->notifier_subscriptions->lock); + } else + mm->notifier_subscriptions->has_itree = true; + + mm_drop_all_locks(mm); + BUG_ON(atomic_read(&mm->mm_users) <= 0); + return 0; + +out_clean: + kfree(subscriptions); + return ret; +} +EXPORT_SYMBOL_GPL(__mmu_notifier_register); + +/** + * mmu_notifier_register - Register a notifier on a mm + * @subscription: The notifier to attach + * @mm: The mm to attach the notifier to + * + * Must not hold mmap_lock 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 subscription->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 *subscription, + struct mm_struct *mm) +{ + int ret; + + mmap_write_lock(mm); + ret = __mmu_notifier_register(subscription, mm); + mmap_write_unlock(mm); + 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 *subscription; + + spin_lock(&mm->notifier_subscriptions->lock); + hlist_for_each_entry_rcu(subscription, + &mm->notifier_subscriptions->list, hlist, + lockdep_is_held(&mm->notifier_subscriptions->lock)) { + if (subscription->ops != ops) + continue; + + if (likely(subscription->users != UINT_MAX)) + subscription->users++; + else + subscription = ERR_PTR(-EOVERFLOW); + spin_unlock(&mm->notifier_subscriptions->lock); + return subscription; + } + spin_unlock(&mm->notifier_subscriptions->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_lock. + * + * 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 *subscription; + int ret; + + mmap_assert_write_locked(mm); + + if (mm->notifier_subscriptions) { + subscription = find_get_mmu_notifier(mm, ops); + if (subscription) + return subscription; + } + + subscription = ops->alloc_notifier(mm); + if (IS_ERR(subscription)) + return subscription; + subscription->ops = ops; + ret = __mmu_notifier_register(subscription, mm); + if (ret) + goto out_free; + return subscription; +out_free: + subscription->ops->free_notifier(subscription); + return ERR_PTR(ret); +} +EXPORT_SYMBOL_GPL(mmu_notifier_get_locked); + +/* this is called after the last mmu_notifier_unregister() returned */ +void __mmu_notifier_subscriptions_destroy(struct mm_struct *mm) +{ + BUG_ON(!hlist_empty(&mm->notifier_subscriptions->list)); + kfree(mm->notifier_subscriptions); + mm->notifier_subscriptions = 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 *subscription, + struct mm_struct *mm) +{ + BUG_ON(atomic_read(&mm->mm_count) <= 0); + + if (!hlist_unhashed(&subscription->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 (subscription->ops->release) + subscription->ops->release(subscription, mm); + srcu_read_unlock(&srcu, id); + + spin_lock(&mm->notifier_subscriptions->lock); + /* + * Can not use list_del_rcu() since __mmu_notifier_release + * can delete it before we hold the lock. + */ + hlist_del_init_rcu(&subscription->hlist); + spin_unlock(&mm->notifier_subscriptions->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 *subscription = + container_of(rcu, struct mmu_notifier, rcu); + struct mm_struct *mm = subscription->mm; + + subscription->ops->free_notifier(subscription); + /* Pairs with the get in __mmu_notifier_register() */ + mmdrop(mm); +} + +/** + * mmu_notifier_put - Release the reference on the notifier + * @subscription: 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 *subscription) +{ + struct mm_struct *mm = subscription->mm; + + spin_lock(&mm->notifier_subscriptions->lock); + if (WARN_ON(!subscription->users) || --subscription->users) + goto out_unlock; + hlist_del_init_rcu(&subscription->hlist); + spin_unlock(&mm->notifier_subscriptions->lock); + + call_srcu(&srcu, &subscription->rcu, mmu_notifier_free_rcu); + return; + +out_unlock: + spin_unlock(&mm->notifier_subscriptions->lock); +} +EXPORT_SYMBOL_GPL(mmu_notifier_put); + +static int __mmu_interval_notifier_insert( + struct mmu_interval_notifier *interval_sub, struct mm_struct *mm, + struct mmu_notifier_subscriptions *subscriptions, unsigned long start, + unsigned long length, const struct mmu_interval_notifier_ops *ops) +{ + interval_sub->mm = mm; + interval_sub->ops = ops; + RB_CLEAR_NODE(&interval_sub->interval_tree.rb); + interval_sub->interval_tree.start = start; + /* + * Note that the representation of the intervals in the interval tree + * considers the ending point as contained in the interval. + */ + if (length == 0 || + check_add_overflow(start, length - 1, + &interval_sub->interval_tree.last)) + return -EOVERFLOW; + + /* Must call with a mmget() held */ + if (WARN_ON(atomic_read(&mm->mm_users) <= 0)) + return -EINVAL; + + /* pairs with mmdrop in mmu_interval_notifier_remove() */ + mmgrab(mm); + + /* + * If some invalidate_range_start/end region is going on in parallel + * we don't know what VA ranges are affected, so we must assume this + * new range is included. + * + * If the itree is invalidating then we are not allowed to change + * it. Retrying until invalidation is done is tricky due to the + * possibility for live lock, instead defer the add to + * mn_itree_inv_end() so this algorithm is deterministic. + * + * In all cases the value for the interval_sub->invalidate_seq should be + * odd, see mmu_interval_read_begin() + */ + spin_lock(&subscriptions->lock); + if (subscriptions->active_invalidate_ranges) { + if (mn_itree_is_invalidating(subscriptions)) + hlist_add_head(&interval_sub->deferred_item, + &subscriptions->deferred_list); + else { + subscriptions->invalidate_seq |= 1; + interval_tree_insert(&interval_sub->interval_tree, + &subscriptions->itree); + } + interval_sub->invalidate_seq = subscriptions->invalidate_seq; + } else { + WARN_ON(mn_itree_is_invalidating(subscriptions)); + /* + * The starting seq for a subscription not under invalidation + * should be odd, not equal to the current invalidate_seq and + * invalidate_seq should not 'wrap' to the new seq any time + * soon. + */ + interval_sub->invalidate_seq = + subscriptions->invalidate_seq - 1; + interval_tree_insert(&interval_sub->interval_tree, + &subscriptions->itree); + } + spin_unlock(&subscriptions->lock); + return 0; +} + +/** + * mmu_interval_notifier_insert - Insert an interval notifier + * @interval_sub: Interval subscription to register + * @start: Starting virtual address to monitor + * @length: Length of the range to monitor + * @mm: mm_struct to attach to + * @ops: Interval notifier operations to be called on matching events + * + * This function subscribes the interval notifier for notifications from the + * mm. Upon return the ops related to mmu_interval_notifier will be called + * whenever an event that intersects with the given range occurs. + * + * Upon return the range_notifier may not be present in the interval tree yet. + * The caller must use the normal interval notifier read flow via + * mmu_interval_read_begin() to establish SPTEs for this range. + */ +int mmu_interval_notifier_insert(struct mmu_interval_notifier *interval_sub, + struct mm_struct *mm, unsigned long start, + unsigned long length, + const struct mmu_interval_notifier_ops *ops) +{ + struct mmu_notifier_subscriptions *subscriptions; + int ret; + + might_lock(&mm->mmap_lock); + + subscriptions = smp_load_acquire(&mm->notifier_subscriptions); + if (!subscriptions || !subscriptions->has_itree) { + ret = mmu_notifier_register(NULL, mm); + if (ret) + return ret; + subscriptions = mm->notifier_subscriptions; + } + return __mmu_interval_notifier_insert(interval_sub, mm, subscriptions, + start, length, ops); +} +EXPORT_SYMBOL_GPL(mmu_interval_notifier_insert); + +int mmu_interval_notifier_insert_locked( + struct mmu_interval_notifier *interval_sub, struct mm_struct *mm, + unsigned long start, unsigned long length, + const struct mmu_interval_notifier_ops *ops) +{ + struct mmu_notifier_subscriptions *subscriptions = + mm->notifier_subscriptions; + int ret; + + mmap_assert_write_locked(mm); + + if (!subscriptions || !subscriptions->has_itree) { + ret = __mmu_notifier_register(NULL, mm); + if (ret) + return ret; + subscriptions = mm->notifier_subscriptions; + } + return __mmu_interval_notifier_insert(interval_sub, mm, subscriptions, + start, length, ops); +} +EXPORT_SYMBOL_GPL(mmu_interval_notifier_insert_locked); + +static bool +mmu_interval_seq_released(struct mmu_notifier_subscriptions *subscriptions, + unsigned long seq) +{ + bool ret; + + spin_lock(&subscriptions->lock); + ret = subscriptions->invalidate_seq != seq; + spin_unlock(&subscriptions->lock); + return ret; +} + +/** + * mmu_interval_notifier_remove - Remove a interval notifier + * @interval_sub: Interval subscription to unregister + * + * This function must be paired with mmu_interval_notifier_insert(). It cannot + * be called from any ops callback. + * + * Once this returns ops callbacks are no longer running on other CPUs and + * will not be called in future. + */ +void mmu_interval_notifier_remove(struct mmu_interval_notifier *interval_sub) +{ + struct mm_struct *mm = interval_sub->mm; + struct mmu_notifier_subscriptions *subscriptions = + mm->notifier_subscriptions; + unsigned long seq = 0; + + might_sleep(); + + spin_lock(&subscriptions->lock); + if (mn_itree_is_invalidating(subscriptions)) { + /* + * remove is being called after insert put this on the + * deferred list, but before the deferred list was processed. + */ + if (RB_EMPTY_NODE(&interval_sub->interval_tree.rb)) { + hlist_del(&interval_sub->deferred_item); + } else { + hlist_add_head(&interval_sub->deferred_item, + &subscriptions->deferred_list); + seq = subscriptions->invalidate_seq; + } + } else { + WARN_ON(RB_EMPTY_NODE(&interval_sub->interval_tree.rb)); + interval_tree_remove(&interval_sub->interval_tree, + &subscriptions->itree); + } + spin_unlock(&subscriptions->lock); + + /* + * The possible sleep on progress in the invalidation requires the + * caller not hold any locks held by invalidation callbacks. + */ + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); + lock_map_release(&__mmu_notifier_invalidate_range_start_map); + if (seq) + wait_event(subscriptions->wq, + mmu_interval_seq_released(subscriptions, seq)); + + /* pairs with mmgrab in mmu_interval_notifier_insert() */ + mmdrop(mm); +} +EXPORT_SYMBOL_GPL(mmu_interval_notifier_remove); + +/** + * 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); |