/* * linux/mm/mmu_notifier.c * * Copyright (C) 2008 Qumranet, Inc. * Copyright (C) 2008 SGI * Christoph Lameter <clameter@sgi.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/module.h> #include <linux/mm.h> #include <linux/err.h> #include <linux/rcupdate.h> #include <linux/sched.h> /* * 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 RCU and it serializes * against the other mmu notifiers with RCU. 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; 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 ->release to finish and * mmu_notifier_unregister to return. */ hlist_del_init_rcu(&mn->hlist); /* * RCU here will block mmu_notifier_unregister until * ->release returns. */ rcu_read_lock(); spin_unlock(&mm->mmu_notifier_mm->lock); /* * 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); rcu_read_unlock(); spin_lock(&mm->mmu_notifier_mm->lock); } spin_unlock(&mm->mmu_notifier_mm->lock); /* * synchronize_rcu here prevents mmu_notifier_release to * return to exit_mmap (which would proceed 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 hold by exit_mmap. */ synchronize_rcu(); } /* * 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 address) { struct mmu_notifier *mn; struct hlist_node *n; int young = 0; rcu_read_lock(); hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) { if (mn->ops->clear_flush_young) young |= mn->ops->clear_flush_young(mn, mm, address); } rcu_read_unlock(); return young; } void __mmu_notifier_invalidate_page(struct mm_struct *mm, unsigned long address) { struct mmu_notifier *mn; struct hlist_node *n; rcu_read_lock(); hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) { if (mn->ops->invalidate_page) mn->ops->invalidate_page(mn, mm, address); } rcu_read_unlock(); } void __mmu_notifier_invalidate_range_start(struct mm_struct *mm, unsigned long start, unsigned long end) { struct mmu_notifier *mn; struct hlist_node *n; rcu_read_lock(); hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) { if (mn->ops->invalidate_range_start) mn->ops->invalidate_range_start(mn, mm, start, end); } rcu_read_unlock(); } void __mmu_notifier_invalidate_range_end(struct mm_struct *mm, unsigned long start, unsigned long end) { struct mmu_notifier *mn; struct hlist_node *n; rcu_read_lock(); hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) { if (mn->ops->invalidate_range_end) mn->ops->invalidate_range_end(mn, mm, start, end); } rcu_read_unlock(); } 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_cleanup; 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; } atomic_inc(&mm->mm_count); /* * 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_cleanup: if (take_mmap_sem) up_write(&mm->mmap_sem); /* kfree() does nothing if mmu_notifier_mm is NULL */ 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 RCU and against mmu_notifier_unregister * with the unregister lock + RCU. 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); spin_lock(&mm->mmu_notifier_mm->lock); if (!hlist_unhashed(&mn->hlist)) { hlist_del_rcu(&mn->hlist); /* * RCU here will force exit_mmap to wait ->release to finish * before freeing the pages. */ rcu_read_lock(); spin_unlock(&mm->mmu_notifier_mm->lock); /* * exit_mmap will block in mmu_notifier_release to * guarantee ->release is called before freeing the * pages. */ if (mn->ops->release) mn->ops->release(mn, mm); rcu_read_unlock(); } else spin_unlock(&mm->mmu_notifier_mm->lock); /* * Wait any running method to finish, of course including * ->release if it was run by mmu_notifier_relase instead of us. */ synchronize_rcu(); BUG_ON(atomic_read(&mm->mm_count) <= 0); mmdrop(mm); } EXPORT_SYMBOL_GPL(mmu_notifier_unregister);