/* * linux/mm/mmu_notifier.c * * Copyright (C) 2008 Qumranet, Inc. * Copyright (C) 2008 SGI * Christoph Lameter <cl@linux.com> * * This work is licensed under the terms of the GNU GPL, version 2. See * the COPYING file in the top-level directory. */ #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); /* * This function allows mmu_notifier::release callback to delay a call to * a function that will free appropriate resources. The function must be * quick and must not block. */ void mmu_notifier_call_srcu(struct rcu_head *rcu, void (*func)(struct rcu_head *rcu)) { call_srcu(&srcu, rcu, func); } EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu); void mmu_notifier_synchronize(void) { /* Wait for any running method to finish. */ srcu_barrier(&srcu); } EXPORT_SYMBOL_GPL(mmu_notifier_synchronize); /* * 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); } void __mmu_notifier_invalidate_range_start(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_start) mn->ops->invalidate_range_start(mn, mm, start, end); } srcu_read_unlock(&srcu, id); } EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start); void __mmu_notifier_invalidate_range_end(struct mm_struct *mm, unsigned long start, unsigned long end, bool only_end) { struct mmu_notifier *mn; int id; id = srcu_read_lock(&srcu); hlist_for_each_entry_rcu(mn, &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, mm, start, end); if (mn->ops->invalidate_range_end) mn->ops->invalidate_range_end(mn, mm, start, end); } srcu_read_unlock(&srcu, id); } EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end); 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); } EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range); /* * Must be called while holding mm->mmap_sem for either read or write. * The result is guaranteed to be valid until mm->mmap_sem is dropped. */ bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm) { struct mmu_notifier *mn; int id; bool ret = false; WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem)); if (!mm_has_notifiers(mm)) return ret; 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_start && !mn->ops->invalidate_range_end) continue; if (!(mn->ops->flags & MMU_INVALIDATE_DOES_NOT_BLOCK)) { ret = true; break; } } srcu_read_unlock(&srcu, id); return ret; } static int do_mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm, int take_mmap_sem) { struct mmu_notifier_mm *mmu_notifier_mm; int ret; BUG_ON(atomic_read(&mm->mm_users) <= 0); ret = -ENOMEM; mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL); if (unlikely(!mmu_notifier_mm)) goto out; if (take_mmap_sem) down_write(&mm->mmap_sem); ret = mm_take_all_locks(mm); if (unlikely(ret)) goto out_clean; if (!mm_has_notifiers(mm)) { INIT_HLIST_HEAD(&mmu_notifier_mm->list); spin_lock_init(&mmu_notifier_mm->lock); mm->mmu_notifier_mm = mmu_notifier_mm; mmu_notifier_mm = NULL; } 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(). */ spin_lock(&mm->mmu_notifier_mm->lock); hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list); spin_unlock(&mm->mmu_notifier_mm->lock); mm_drop_all_locks(mm); out_clean: if (take_mmap_sem) up_write(&mm->mmap_sem); kfree(mmu_notifier_mm); out: BUG_ON(atomic_read(&mm->mm_users) <= 0); return ret; } /* * 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 must be always called to * unregister the notifier. mm_count is automatically pinned to allow * mmu_notifier_unregister to safely run at any time later, before or * after exit_mmap. ->release will always be called before exit_mmap * frees the pages. */ int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm) { return do_mmu_notifier_register(mn, mm, 1); } EXPORT_SYMBOL_GPL(mmu_notifier_register); /* * 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) { return do_mmu_notifier_register(mn, mm, 0); } EXPORT_SYMBOL_GPL(__mmu_notifier_register); /* 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); /* * Same as mmu_notifier_unregister but no callback and no srcu synchronization. */ void mmu_notifier_unregister_no_release(struct mmu_notifier *mn, struct mm_struct *mm) { 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); BUG_ON(atomic_read(&mm->mm_count) <= 0); mmdrop(mm); } EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);