1 files changed, 277 insertions, 0 deletions

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
new file mode 100644
index 000000000000..5f4ef0250bee
--- /dev/null
+++ b/mm/mmu_notifier.c
@@ -0,0 +1,277 @@
+/*
+ *  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);