IB/core: Implement support for MMU notifiers regarding on demand paging regions

* Add an interval tree implementation for ODP umems. Create an
  interval tree for each ucontext (including a count of the number of
  ODP MRs in this context, semaphore, etc.), and register ODP umems in
  the interval tree.
* Add MMU notifiers handling functions, using the interval tree to
  notify only the relevant umems and underlying MRs.
* Register to receive MMU notifier events from the MM subsystem upon
  ODP MR registration (and unregister accordingly).
* Add a completion object to synchronize the destruction of ODP umems.
* Add mechanism to abort page faults when there's a concurrent invalidation.

The way we synchronize between concurrent invalidations and page
faults is by keeping a counter of currently running invalidations, and
a sequence number that is incremented whenever an invalidation is
caught. The page fault code checks the counter and also verifies that
the sequence number hasn't progressed before it updates the umem's
page tables. This is similar to what the kvm module does.

In order to prevent the case where we register a umem in the middle of
an ongoing notifier, we also keep a per ucontext counter of the total
number of active mmu notifiers. We only enable new umems when all the
running notifiers complete.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Shachar Raindel <raindel@mellanox.com>
Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Yuval Dagan <yuvalda@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 369 insertions, 10 deletions

diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index f889e8d793bd..6095872549e7 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -41,26 +41,235 @@
 #include <rdma/ib_umem.h>
 #include <rdma/ib_umem_odp.h>
 
+static void ib_umem_notifier_start_account(struct ib_umem *item)
+{
+	mutex_lock(&item->odp_data->umem_mutex);
+
+	/* Only update private counters for this umem if it has them.
+	 * Otherwise skip it. All page faults will be delayed for this umem. */
+	if (item->odp_data->mn_counters_active) {
+		int notifiers_count = item->odp_data->notifiers_count++;
+
+		if (notifiers_count == 0)
+			/* Initialize the completion object for waiting on
+			 * notifiers. Since notifier_count is zero, no one
+			 * should be waiting right now. */
+			reinit_completion(&item->odp_data->notifier_completion);
+	}
+	mutex_unlock(&item->odp_data->umem_mutex);
+}
+
+static void ib_umem_notifier_end_account(struct ib_umem *item)
+{
+	mutex_lock(&item->odp_data->umem_mutex);
+
+	/* Only update private counters for this umem if it has them.
+	 * Otherwise skip it. All page faults will be delayed for this umem. */
+	if (item->odp_data->mn_counters_active) {
+		/*
+		 * This sequence increase will notify the QP page fault that
+		 * the page that is going to be mapped in the spte could have
+		 * been freed.
+		 */
+		++item->odp_data->notifiers_seq;
+		if (--item->odp_data->notifiers_count == 0)
+			complete_all(&item->odp_data->notifier_completion);
+	}
+	mutex_unlock(&item->odp_data->umem_mutex);
+}
+
+/* Account for a new mmu notifier in an ib_ucontext. */
+static void ib_ucontext_notifier_start_account(struct ib_ucontext *context)
+{
+	atomic_inc(&context->notifier_count);
+}
+
+/* Account for a terminating mmu notifier in an ib_ucontext.
+ *
+ * Must be called with the ib_ucontext->umem_rwsem semaphore unlocked, since
+ * the function takes the semaphore itself. */
+static void ib_ucontext_notifier_end_account(struct ib_ucontext *context)
+{
+	int zero_notifiers = atomic_dec_and_test(&context->notifier_count);
+
+	if (zero_notifiers &&
+	    !list_empty(&context->no_private_counters)) {
+		/* No currently running mmu notifiers. Now is the chance to
+		 * add private accounting to all previously added umems. */
+		struct ib_umem_odp *odp_data, *next;
+
+		/* Prevent concurrent mmu notifiers from working on the
+		 * no_private_counters list. */
+		down_write(&context->umem_rwsem);
+
+		/* Read the notifier_count again, with the umem_rwsem
+		 * semaphore taken for write. */
+		if (!atomic_read(&context->notifier_count)) {
+			list_for_each_entry_safe(odp_data, next,
+						 &context->no_private_counters,
+						 no_private_counters) {
+				mutex_lock(&odp_data->umem_mutex);
+				odp_data->mn_counters_active = true;
+				list_del(&odp_data->no_private_counters);
+				complete_all(&odp_data->notifier_completion);
+				mutex_unlock(&odp_data->umem_mutex);
+			}
+		}
+
+		up_write(&context->umem_rwsem);
+	}
+}
+
+static int ib_umem_notifier_release_trampoline(struct ib_umem *item, u64 start,
+					       u64 end, void *cookie) {
+	/*
+	 * Increase the number of notifiers running, to
+	 * prevent any further fault handling on this MR.
+	 */
+	ib_umem_notifier_start_account(item);
+	item->odp_data->dying = 1;
+	/* Make sure that the fact the umem is dying is out before we release
+	 * all pending page faults. */
+	smp_wmb();
+	complete_all(&item->odp_data->notifier_completion);
+	item->context->invalidate_range(item, ib_umem_start(item),
+					ib_umem_end(item));
+	return 0;
+}
+
+static void ib_umem_notifier_release(struct mmu_notifier *mn,
+				     struct mm_struct *mm)
+{
+	struct ib_ucontext *context = container_of(mn, struct ib_ucontext, mn);
+
+	if (!context->invalidate_range)
+		return;
+
+	ib_ucontext_notifier_start_account(context);
+	down_read(&context->umem_rwsem);
+	rbt_ib_umem_for_each_in_range(&context->umem_tree, 0,
+				      ULLONG_MAX,
+				      ib_umem_notifier_release_trampoline,
+				      NULL);
+	up_read(&context->umem_rwsem);
+}
+
+static int invalidate_page_trampoline(struct ib_umem *item, u64 start,
+				      u64 end, void *cookie)
+{
+	ib_umem_notifier_start_account(item);
+	item->context->invalidate_range(item, start, start + PAGE_SIZE);
+	ib_umem_notifier_end_account(item);
+	return 0;
+}
+
+static void ib_umem_notifier_invalidate_page(struct mmu_notifier *mn,
+					     struct mm_struct *mm,
+					     unsigned long address)
+{
+	struct ib_ucontext *context = container_of(mn, struct ib_ucontext, mn);
+
+	if (!context->invalidate_range)
+		return;
+
+	ib_ucontext_notifier_start_account(context);
+	down_read(&context->umem_rwsem);
+	rbt_ib_umem_for_each_in_range(&context->umem_tree, address,
+				      address + PAGE_SIZE,
+				      invalidate_page_trampoline, NULL);
+	up_read(&context->umem_rwsem);
+	ib_ucontext_notifier_end_account(context);
+}
+
+static int invalidate_range_start_trampoline(struct ib_umem *item, u64 start,
+					     u64 end, void *cookie)
+{
+	ib_umem_notifier_start_account(item);
+	item->context->invalidate_range(item, start, end);
+	return 0;
+}
+
+static void ib_umem_notifier_invalidate_range_start(struct mmu_notifier *mn,
+						    struct mm_struct *mm,
+						    unsigned long start,
+						    unsigned long end)
+{
+	struct ib_ucontext *context = container_of(mn, struct ib_ucontext, mn);
+
+	if (!context->invalidate_range)
+		return;
+
+	ib_ucontext_notifier_start_account(context);
+	down_read(&context->umem_rwsem);
+	rbt_ib_umem_for_each_in_range(&context->umem_tree, start,
+				      end,
+				      invalidate_range_start_trampoline, NULL);
+	up_read(&context->umem_rwsem);
+}
+
+static int invalidate_range_end_trampoline(struct ib_umem *item, u64 start,
+					   u64 end, void *cookie)
+{
+	ib_umem_notifier_end_account(item);
+	return 0;
+}
+
+static void ib_umem_notifier_invalidate_range_end(struct mmu_notifier *mn,
+						  struct mm_struct *mm,
+						  unsigned long start,
+						  unsigned long end)
+{
+	struct ib_ucontext *context = container_of(mn, struct ib_ucontext, mn);
+
+	if (!context->invalidate_range)
+		return;
+
+	down_read(&context->umem_rwsem);
+	rbt_ib_umem_for_each_in_range(&context->umem_tree, start,
+				      end,
+				      invalidate_range_end_trampoline, NULL);
+	up_read(&context->umem_rwsem);
+	ib_ucontext_notifier_end_account(context);
+}
+
+static struct mmu_notifier_ops ib_umem_notifiers = {
+	.release                    = ib_umem_notifier_release,
+	.invalidate_page            = ib_umem_notifier_invalidate_page,
+	.invalidate_range_start     = ib_umem_notifier_invalidate_range_start,
+	.invalidate_range_end       = ib_umem_notifier_invalidate_range_end,
+};
+
 int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem)
 {
 	int ret_val;
 	struct pid *our_pid;
+	struct mm_struct *mm = get_task_mm(current);
+
+	if (!mm)
+		return -EINVAL;
 
 	/* Prevent creating ODP MRs in child processes */
 	rcu_read_lock();
 	our_pid = get_task_pid(current->group_leader, PIDTYPE_PID);
 	rcu_read_unlock();
 	put_pid(our_pid);
-	if (context->tgid != our_pid)
-		return -EINVAL;
+	if (context->tgid != our_pid) {
+		ret_val = -EINVAL;
+		goto out_mm;
+	}
 
 	umem->hugetlb = 0;
 	umem->odp_data = kzalloc(sizeof(*umem->odp_data), GFP_KERNEL);
-	if (!umem->odp_data)
-		return -ENOMEM;
+	if (!umem->odp_data) {
+		ret_val = -ENOMEM;
+		goto out_mm;
+	}
+	umem->odp_data->umem = umem;
 
 	mutex_init(&umem->odp_data->umem_mutex);
 
+	init_completion(&umem->odp_data->notifier_completion);
+
 	umem->odp_data->page_list = vzalloc(ib_umem_num_pages(umem) *
 					    sizeof(*umem->odp_data->page_list));
 	if (!umem->odp_data->page_list) {
@@ -75,17 +284,72 @@ int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem)
 		goto out_page_list;
 	}
 
+	/*
+	 * When using MMU notifiers, we will get a
+	 * notification before the "current" task (and MM) is
+	 * destroyed. We use the umem_rwsem semaphore to synchronize.
+	 */
+	down_write(&context->umem_rwsem);
+	context->odp_mrs_count++;
+	if (likely(ib_umem_start(umem) != ib_umem_end(umem)))
+		rbt_ib_umem_insert(&umem->odp_data->interval_tree,
+				   &context->umem_tree);
+	if (likely(!atomic_read(&context->notifier_count)))
+		umem->odp_data->mn_counters_active = true;
+	else
+		list_add(&umem->odp_data->no_private_counters,
+			 &context->no_private_counters);
+	downgrade_write(&context->umem_rwsem);
+
+	if (context->odp_mrs_count == 1) {
+		/*
+		 * Note that at this point, no MMU notifier is running
+		 * for this context!
+		 */
+		atomic_set(&context->notifier_count, 0);
+		INIT_HLIST_NODE(&context->mn.hlist);
+		context->mn.ops = &ib_umem_notifiers;
+		/*
+		 * Lock-dep detects a false positive for mmap_sem vs.
+		 * umem_rwsem, due to not grasping downgrade_write correctly.
+		 */
+		lockdep_off();
+		ret_val = mmu_notifier_register(&context->mn, mm);
+		lockdep_on();
+		if (ret_val) {
+			pr_err("Failed to register mmu_notifier %d\n", ret_val);
+			ret_val = -EBUSY;
+			goto out_mutex;
+		}
+	}
+
+	up_read(&context->umem_rwsem);
+
+	/*
+	 * Note that doing an mmput can cause a notifier for the relevant mm.
+	 * If the notifier is called while we hold the umem_rwsem, this will
+	 * cause a deadlock. Therefore, we release the reference only after we
+	 * released the semaphore.
+	 */
+	mmput(mm);
 	return 0;
 
+out_mutex:
+	up_read(&context->umem_rwsem);
+	vfree(umem->odp_data->dma_list);
 out_page_list:
 	vfree(umem->odp_data->page_list);
 out_odp_data:
 	kfree(umem->odp_data);
+out_mm:
+	mmput(mm);
 	return ret_val;
 }
 
 void ib_umem_odp_release(struct ib_umem *umem)
 {
+	struct ib_ucontext *context = umem->context;
+
 	/*
 	 * Ensure that no more pages are mapped in the umem.
 	 *
@@ -95,6 +359,54 @@ void ib_umem_odp_release(struct ib_umem *umem)
 	ib_umem_odp_unmap_dma_pages(umem, ib_umem_start(umem),
 				    ib_umem_end(umem));
 
+	down_write(&context->umem_rwsem);
+	if (likely(ib_umem_start(umem) != ib_umem_end(umem)))
+		rbt_ib_umem_remove(&umem->odp_data->interval_tree,
+				   &context->umem_tree);
+	context->odp_mrs_count--;
+	if (!umem->odp_data->mn_counters_active) {
+		list_del(&umem->odp_data->no_private_counters);
+		complete_all(&umem->odp_data->notifier_completion);
+	}
+
+	/*
+	 * Downgrade the lock to a read lock. This ensures that the notifiers
+	 * (who lock the mutex for reading) will be able to finish, and we
+	 * will be able to enventually obtain the mmu notifiers SRCU. Note
+	 * that since we are doing it atomically, no other user could register
+	 * and unregister while we do the check.
+	 */
+	downgrade_write(&context->umem_rwsem);
+	if (!context->odp_mrs_count) {
+		struct task_struct *owning_process = NULL;
+		struct mm_struct *owning_mm        = NULL;
+
+		owning_process = get_pid_task(context->tgid,
+					      PIDTYPE_PID);
+		if (owning_process == NULL)
+			/*
+			 * The process is already dead, notifier were removed
+			 * already.
+			 */
+			goto out;
+
+		owning_mm = get_task_mm(owning_process);
+		if (owning_mm == NULL)
+			/*
+			 * The process' mm is already dead, notifier were
+			 * removed already.
+			 */
+			goto out_put_task;
+		mmu_notifier_unregister(&context->mn, owning_mm);
+
+		mmput(owning_mm);
+
+out_put_task:
+		put_task_struct(owning_process);
+	}
+out:
+	up_read(&context->umem_rwsem);
+
 	vfree(umem->odp_data->dma_list);
 	vfree(umem->odp_data->page_list);
 	kfree(umem->odp_data);
@@ -112,7 +424,8 @@ void ib_umem_odp_release(struct ib_umem *umem)
  *               the sequence number is taken from
  *               umem->odp_data->notifiers_seq.
  *
- * The function returns -EFAULT if the DMA mapping operation fails.
+ * The function returns -EFAULT if the DMA mapping operation fails. It returns
+ * -EAGAIN if a concurrent invalidation prevents us from updating the page.
  *
  * The page is released via put_page even if the operation failed. For
  * on-demand pinning, the page is released whenever it isn't stored in the
@@ -121,6 +434,7 @@ void ib_umem_odp_release(struct ib_umem *umem)
 static int ib_umem_odp_map_dma_single_page(
 		struct ib_umem *umem,
 		int page_index,
+		u64 base_virt_addr,
 		struct page *page,
 		u64 access_mask,
 		unsigned long current_seq)
@@ -128,9 +442,19 @@ static int ib_umem_odp_map_dma_single_page(
 	struct ib_device *dev = umem->context->device;
 	dma_addr_t dma_addr;
 	int stored_page = 0;
+	int remove_existing_mapping = 0;
 	int ret = 0;
 
 	mutex_lock(&umem->odp_data->umem_mutex);
+	/*
+	 * Note: we avoid writing if seq is different from the initial seq, to
+	 * handle case of a racing notifier. This check also allows us to bail
+	 * early if we have a notifier running in parallel with us.
+	 */
+	if (ib_umem_mmu_notifier_retry(umem, current_seq)) {
+		ret = -EAGAIN;
+		goto out;
+	}
 	if (!(umem->odp_data->dma_list[page_index])) {
 		dma_addr = ib_dma_map_page(dev,
 					   page,
@@ -148,14 +472,27 @@ static int ib_umem_odp_map_dma_single_page(
 	} else {
 		pr_err("error: got different pages in IB device and from get_user_pages. IB device page: %p, gup page: %p\n",
 		       umem->odp_data->page_list[page_index], page);
+		/* Better remove the mapping now, to prevent any further
+		 * damage. */
+		remove_existing_mapping = 1;
 	}
 
 out:
 	mutex_unlock(&umem->odp_data->umem_mutex);
 
-	if (!stored_page)
+	/* On Demand Paging - avoid pinning the page */
+	if (umem->context->invalidate_range || !stored_page)
 		put_page(page);
 
+	if (remove_existing_mapping && umem->context->invalidate_range) {
+		invalidate_page_trampoline(
+			umem,
+			base_virt_addr + (page_index * PAGE_SIZE),
+			base_virt_addr + ((page_index+1)*PAGE_SIZE),
+			NULL);
+		ret = -EAGAIN;
+	}
+
 	return ret;
 }
 
@@ -168,6 +505,8 @@ out:
  *
  * Returns the number of pages mapped in success, negative error code
  * for failure.
+ * An -EAGAIN error code is returned when a concurrent mmu notifier prevents
+ * the function from completing its task.
  *
  * @umem: the umem to map and pin
  * @user_virt: the address from which we need to map.
@@ -189,6 +528,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
 	struct page       **local_page_list = NULL;
 	u64 off;
 	int j, k, ret = 0, start_idx, npages = 0;
+	u64 base_virt_addr;
 
 	if (access_mask == 0)
 		return -EINVAL;
@@ -203,6 +543,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
 
 	off = user_virt & (~PAGE_MASK);
 	user_virt = user_virt & PAGE_MASK;
+	base_virt_addr = user_virt;
 	bcnt += off; /* Charge for the first page offset as well. */
 
 	owning_process = get_pid_task(umem->context->tgid, PIDTYPE_PID);
@@ -246,8 +587,8 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
 		user_virt += npages << PAGE_SHIFT;
 		for (j = 0; j < npages; ++j) {
 			ret = ib_umem_odp_map_dma_single_page(
-				umem, k, local_page_list[j], access_mask,
-				current_seq);
+				umem, k, base_virt_addr, local_page_list[j],
+				access_mask, current_seq);
 			if (ret < 0)
 				break;
 			k++;
@@ -286,6 +627,11 @@ void ib_umem_odp_unmap_dma_pages(struct ib_umem *umem, u64 virt,
 
 	virt  = max_t(u64, virt,  ib_umem_start(umem));
 	bound = min_t(u64, bound, ib_umem_end(umem));
+	/* Note that during the run of this function, the
+	 * notifiers_count of the MR is > 0, preventing any racing
+	 * faults from completion. We might be racing with other
+	 * invalidations, so we must make sure we free each page only
+	 * once. */
 	for (addr = virt; addr < bound; addr += (u64)umem->page_size) {
 		idx = (addr - ib_umem_start(umem)) / PAGE_SIZE;
 		mutex_lock(&umem->odp_data->umem_mutex);
@@ -300,8 +646,21 @@ void ib_umem_odp_unmap_dma_pages(struct ib_umem *umem, u64 virt,
 			ib_dma_unmap_page(dev, dma_addr, PAGE_SIZE,
 					  DMA_BIDIRECTIONAL);
 			if (dma & ODP_WRITE_ALLOWED_BIT)
-				set_page_dirty_lock(head_page);
-			put_page(page);
+				/*
+				 * set_page_dirty prefers being called with
+				 * the page lock. However, MMU notifiers are
+				 * called sometimes with and sometimes without
+				 * the lock. We rely on the umem_mutex instead
+				 * to prevent other mmu notifiers from
+				 * continuing and allowing the page mapping to
+				 * be removed.
+				 */
+				set_page_dirty(head_page);
+			/* on demand pinning support */
+			if (!umem->context->invalidate_range)
+				put_page(page);
+			umem->odp_data->page_list[idx] = NULL;
+			umem->odp_data->dma_list[idx] = 0;
 		}
 		mutex_unlock(&umem->odp_data->umem_mutex);
 	}