[PATCH v3 10/14] iommu/ioasid: Introduce notification APIs

[Jacob Pan]

Relations among IOASID users largely follow a publisher-subscriber
pattern. E.g. to support guest SVA on Intel Scalable I/O Virtualization
(SIOV) enabled platforms, VFIO, IOMMU, device drivers, KVM are all users
of IOASIDs. When a state change occurs, VFIO publishes the change event
that needs to be processed by other users/subscribers.

This patch introduced two types of notifications: global and per
ioasid_set. The latter is intended for users who only needs to handle
events related to the IOASID of a given set.
For more information, refer to the kernel documentation at
Documentation/ioasid.rst.

Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/ioasid.c | 141 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/ioasid.h |  57 +++++++++++++++++++-
 2 files changed, 197 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 378fef8f23d9..894b17c06ead 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -10,12 +10,35 @@
 #include <linux/spinlock.h>
 #include <linux/xarray.h>
 
+/*
+ * An IOASID can have multiple consumers where each consumer may have
+ * hardware contexts associated with the IOASID.
+ * When a status change occurs, like on IOASID deallocation, notifier chains
+ * are used to keep the consumers in sync.
+ * This is a publisher-subscriber pattern where publisher can change the
+ * state of each IOASID, e.g. alloc/free, bind IOASID to a device and mm.
+ * On the other hand, subscribers get notified for the state change and
+ * keep local states in sync.
+ */
+static ATOMIC_NOTIFIER_HEAD(ioasid_notifier);
+/* List to hold pending notification block registrations */
+static LIST_HEAD(ioasid_nb_pending_list);
+static DEFINE_SPINLOCK(ioasid_nb_lock);
+
 /* Default to PCIe standard 20 bit PASID */
 #define PCI_PASID_MAX 0x100000
 static ioasid_t ioasid_capacity = PCI_PASID_MAX;
 static ioasid_t ioasid_capacity_avail = PCI_PASID_MAX;
 static DEFINE_XARRAY_ALLOC(ioasid_sets);
 
+struct ioasid_set_nb {
+	struct list_head	list;
+	struct notifier_block	*nb;
+	void			*token;
+	struct ioasid_set	*set;
+	bool			active;
+};
+
 enum ioasid_state {
 	IOASID_STATE_INACTIVE,
 	IOASID_STATE_ACTIVE,
@@ -365,6 +388,42 @@ void ioasid_detach_data(ioasid_t ioasid)
 }
 EXPORT_SYMBOL_GPL(ioasid_detach_data);
 
+/**
+ * ioasid_notify - Send notification on a given IOASID for status change.
+ *
+ * @data:	The IOASID data to which the notification will send
+ * @cmd:	Notification event sent by IOASID external users, can be
+ *		IOASID_BIND or IOASID_UNBIND.
+ *
+ * @flags:	Special instructions, e.g. notify within a set or global by
+ *		IOASID_NOTIFY_FLAG_SET or IOASID_NOTIFY_FLAG_ALL flags
+ * Caller must hold ioasid_allocator_lock and reference to the IOASID
+ */
+static int ioasid_notify(struct ioasid_data *data,
+			 enum ioasid_notify_val cmd, unsigned int flags)
+{
+	struct ioasid_nb_args args = { 0 };
+	int ret = 0;
+
+	/* IOASID_FREE/ALLOC are internal events emitted by IOASID core only */
+	if (cmd <= IOASID_NOTIFY_FREE)
+		return -EINVAL;
+
+	if (flags & ~(IOASID_NOTIFY_FLAG_ALL | IOASID_NOTIFY_FLAG_SET))
+		return -EINVAL;
+
+	args.id = data->id;
+	args.set = data->set;
+	args.pdata = data->private;
+	args.spid = data->spid;
+	if (flags & IOASID_NOTIFY_FLAG_ALL)
+		ret = atomic_notifier_call_chain(&ioasid_notifier, cmd, &args);
+	if (flags & IOASID_NOTIFY_FLAG_SET)
+		ret = atomic_notifier_call_chain(&data->set->nh, cmd, &args);
+
+	return ret;
+}
+
 static ioasid_t ioasid_find_by_spid_locked(struct ioasid_set *set, ioasid_t spid)
 {
 	ioasid_t ioasid = INVALID_IOASID;
@@ -417,6 +476,7 @@ int ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid)
 		goto done_unlock;
 	}
 	data->spid = spid;
+	ioasid_notify(data, IOASID_NOTIFY_BIND, IOASID_NOTIFY_FLAG_SET);
 
 done_unlock:
 	spin_unlock(&ioasid_allocator_lock);
@@ -436,6 +496,7 @@ void ioasid_detach_spid(ioasid_t ioasid)
 		goto done_unlock;
 	}
 	data->spid = INVALID_IOASID;
+	ioasid_notify(data, IOASID_NOTIFY_UNBIND, IOASID_NOTIFY_FLAG_SET);
 
 done_unlock:
 	spin_unlock(&ioasid_allocator_lock);
@@ -469,6 +530,28 @@ static inline bool ioasid_set_is_valid(struct ioasid_set *set)
 	return xa_load(&ioasid_sets, set->id) == set;
 }
 
+static void ioasid_add_pending_nb(struct ioasid_set *set)
+{
+	struct ioasid_set_nb *curr;
+
+	if (set->type != IOASID_SET_TYPE_MM)
+		return;
+
+	/*
+	 * Check if there are any pending nb requests for the given token, if so
+	 * add them to the notifier chain.
+	 */
+	spin_lock(&ioasid_nb_lock);
+	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
+		if (curr->token == set->token && !curr->active) {
+			atomic_notifier_chain_register(&set->nh, curr->nb);
+			curr->set = set;
+			curr->active = true;
+		}
+	}
+	spin_unlock(&ioasid_nb_lock);
+}
+
 /**
  * ioasid_set_alloc - Allocate a new IOASID set for a given token
  *
@@ -556,6 +639,13 @@ struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, int type)
 	set->quota = quota;
 	set->id = id;
 	refcount_set(&set->ref, 1);
+	ATOMIC_INIT_NOTIFIER_HEAD(&set->nh);
+
+	/*
+	 * Check if there are any pending nb requests for the given token, if so
+	 * add them to the notifier chain.
+	 */
+	ioasid_add_pending_nb(set);
 
 	/*
 	 * Per set XA is used to store private IDs within the set, get ready
@@ -641,6 +731,7 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 		goto exit_free;
 	}
 	set->nr_ioasids++;
+	ioasid_notify(data, IOASID_NOTIFY_ALLOC, IOASID_NOTIFY_FLAG_SET);
 	goto done_unlock;
 exit_free:
 	kfree(data);
@@ -687,6 +778,8 @@ static void ioasid_free_locked(struct ioasid_set *set, ioasid_t ioasid)
 		return;
 
 	data->state = IOASID_STATE_FREE_PENDING;
+	ioasid_notify(data, IOASID_NOTIFY_FREE,
+		      IOASID_NOTIFY_FLAG_ALL | IOASID_NOTIFY_FLAG_ALL);
 	if (!refcount_dec_and_test(&data->users))
 		return;
 
@@ -726,6 +819,7 @@ EXPORT_SYMBOL_GPL(ioasid_set_get);
 
 static void ioasid_set_put_locked(struct ioasid_set *set)
 {
+	struct ioasid_set_nb *curr;
 	struct ioasid_data *entry;
 	unsigned long index;
 
@@ -757,6 +851,16 @@ static void ioasid_set_put_locked(struct ioasid_set *set)
 	/* Return the quota back to system pool */
 	ioasid_capacity_avail += set->quota;
 
+	/* Restore pending status of the set NBs */
+	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
+		if (curr->token == set->token) {
+			if (curr->active)
+				curr->active = false;
+			else
+				pr_warn("Set token exists but not active!\n");
+		}
+	}
+
 	/*
 	 * Token got released right away after the ioasid_set is freed.
 	 * If a new set is created immediately with the newly released token,
@@ -778,7 +882,9 @@ static void ioasid_set_put_locked(struct ioasid_set *set)
 void ioasid_set_put(struct ioasid_set *set)
 {
 	spin_lock(&ioasid_allocator_lock);
+	spin_lock(&ioasid_nb_lock);
 	ioasid_set_put_locked(set);
+	spin_unlock(&ioasid_nb_lock);
 	spin_unlock(&ioasid_allocator_lock);
 }
 EXPORT_SYMBOL_GPL(ioasid_set_put);
@@ -980,6 +1086,41 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 }
 EXPORT_SYMBOL_GPL(ioasid_find);
 
+int ioasid_register_notifier(struct ioasid_set *set, struct notifier_block *nb)
+{
+	if (set)
+		return atomic_notifier_chain_register(&set->nh, nb);
+	else
+		return atomic_notifier_chain_register(&ioasid_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(ioasid_register_notifier);
+
+void ioasid_unregister_notifier(struct ioasid_set *set,
+				struct notifier_block *nb)
+{
+	struct ioasid_set_nb *curr;
+
+	spin_lock(&ioasid_nb_lock);
+	/*
+	 * Pending list is registered with a token without an ioasid_set,
+	 * therefore should not be unregistered directly.
+	 */
+	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
+		if (curr->nb == nb) {
+			pr_warn("Cannot unregister NB from pending list\n");
+			spin_unlock(&ioasid_nb_lock);
+			return;
+		}
+	}
+	spin_unlock(&ioasid_nb_lock);
+
+	if (set)
+		atomic_notifier_chain_unregister(&set->nh, nb);
+	else
+		atomic_notifier_chain_unregister(&ioasid_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(ioasid_unregister_notifier);
+
 MODULE_AUTHOR("Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>");
 MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>");
 MODULE_DESCRIPTION("IO Address Space ID (IOASID) allocator");
diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 2dfe85e6cb7e..1b551c99d568 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -23,6 +23,7 @@ enum ioasid_set_type {
 
 /**
  * struct ioasid_set - Meta data about ioasid_set
+ * @nh:		List of notifiers private to that set
  * @xa:		XArray to store ioasid_set private IDs, can be used for
  *		guest-host IOASID mapping, or just a private IOASID namespace.
  * @token:	Unique to identify an IOASID set
@@ -33,6 +34,7 @@ enum ioasid_set_type {
  * @ref:	Reference count of the users
  */
 struct ioasid_set {
+	struct atomic_notifier_head nh;
 	struct xarray xa;
 	void *token;
 	int type;
@@ -58,6 +60,47 @@ struct ioasid_allocator_ops {
 	void *pdata;
 };
 
+/* Notification data when IOASID status changed */
+enum ioasid_notify_val {
+	IOASID_NOTIFY_ALLOC = 1,
+	IOASID_NOTIFY_FREE,
+	IOASID_NOTIFY_BIND,
+	IOASID_NOTIFY_UNBIND,
+};
+
+#define IOASID_NOTIFY_FLAG_ALL BIT(0)
+#define IOASID_NOTIFY_FLAG_SET BIT(1)
+/**
+ * enum ioasid_notifier_prios - IOASID event notification order
+ *
+ * When status of an IOASID changes, users might need to take actions to
+ * reflect the new state. For example, when an IOASID is freed due to
+ * exception, the hardware context in virtual CPU, DMA device, and IOMMU
+ * shall be cleared and drained. Order is required to prevent life cycle
+ * problems.
+ */
+enum ioasid_notifier_prios {
+	IOASID_PRIO_LAST,
+	IOASID_PRIO_DEVICE,
+	IOASID_PRIO_IOMMU,
+	IOASID_PRIO_CPU,
+};
+
+/**
+ * struct ioasid_nb_args - Argument provided by IOASID core when notifier
+ * is called.
+ * @id:		The IOASID being notified
+ * @spid:	The set private ID associated with the IOASID
+ * @set:	The IOASID set of @id
+ * @pdata:	The private data attached to the IOASID
+ */
+struct ioasid_nb_args {
+	ioasid_t id;
+	ioasid_t spid;
+	struct ioasid_set *set;
+	void *pdata;
+};
+
 #if IS_ENABLED(CONFIG_IOASID)
 void ioasid_install_capacity(ioasid_t total);
 ioasid_t ioasid_get_capacity(void);
@@ -82,7 +125,10 @@ void ioasid_detach_data(ioasid_t ioasid);
 int ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid);
 void ioasid_detach_spid(ioasid_t ioasid);
 ioasid_t ioasid_find_by_spid(struct ioasid_set *set, ioasid_t spid);
-
+int ioasid_register_notifier(struct ioasid_set *set,
+			struct notifier_block *nb);
+void ioasid_unregister_notifier(struct ioasid_set *set,
+				struct notifier_block *nb);
 void ioasid_set_for_each_ioasid(struct ioasid_set *sdata,
 				void (*fn)(ioasid_t id, void *data),
 				void *data);
@@ -145,6 +191,15 @@ static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid, bool (*
 	return NULL;
 }
 
+static inline int ioasid_register_notifier(struct notifier_block *nb)
+{
+	return -ENOTSUPP;
+}
+
+static inline void ioasid_unregister_notifier(struct notifier_block *nb)
+{
+}
+
 static inline int ioasid_register_allocator(struct ioasid_allocator_ops *allocator)
 {
 	return -ENOTSUPP;
-- 
2.7.4