[PATCH v8 3/4] tee: optee: support tracking system threads

[Etienne Carriere]

Adds support in the OP-TEE driver to keep track of reserved system
threads. The optee_cq_*() functions are updated to handle this if
enabled. The SMC ABI part of the driver enables this tracking, but the
FF-A ABI part does not.

The call queue list optee_call_queue::waiters is replaced by 2 lists,
one for regular sessions and one system sessions. The struct also
stores count of TEE thread contexts provisioned/used/reserved to
track use of TEE resources. The logic allows at most 1 OP-TEE entry
can be reserved to TEE system sessions. For sake of simplicity,
initialization of call queue management is factorized into new
helper function optee_cq_init().

Co-developed-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
Signed-off-by: Etienne Carriere <etienne.carriere@xxxxxxxxxx>
---
Changes since v7:
- Changes the logic to reserve at most 1 call entry for system sessions
  as per patches v6 and v7 discussion threads (the 2 below bullets)
  and updates commit message accordingly.
- Field optee_call_queue::res_sys_thread_count is replaced with 2 fields:
  sys_thread_req_count and boolean sys_thread_in_use.
- Field optee_call_waiter::sys_thread is replaced with 2 fields:
  sys_thread_req and sys_thread_used.
- Adds inline description comments for struct optee_call_queue and
  struct optee_call_waiter.

Changes since v6:
- Moved out changes related to adding boolean system thread attribute
  into optee driver call queue and SMC/FF-A ABIs API functions. These
  changes were squashed into patch 1/4 of this patch v7 series.
- Comment about adding a specific commit for call queue refactoring
  was not addressed such a patch would only introduce function
  optee_cq_init()  with very little content in (mutex & list init).
- Added Co-developed-by tag for Jens contribution as he's not responsible
  for the changes I made in this patch v7.

No change since v5

Changes since v4:
- New change that supersedes implementation proposed in PATCH v4
  (tee: system invocation"). Thanks to Jens implementation we don't need
  the new OP-TEE services that my previous patch versions introduced to
  monitor system threads entry. Now, Linux optee SMC ABI driver gets TEE
  provisioned thread contexts count once and monitors thread entries in
  OP-TEE on that basis and the system thread capability of the related
  tee session. By the way, I dropped the WARN_ONCE() call I suggested
  on tee thread exhaustion as it does not provides useful information.
---
 drivers/tee/optee/call.c          | 131 ++++++++++++++++++++++++++++--
 drivers/tee/optee/ffa_abi.c       |   3 +-
 drivers/tee/optee/optee_private.h |  30 ++++++-
 drivers/tee/optee/smc_abi.c       |  16 +++-
 4 files changed, 167 insertions(+), 13 deletions(-)

diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c
index 152ae9bb1785..7aec64f0f7e0 100644
--- a/drivers/tee/optee/call.c
+++ b/drivers/tee/optee/call.c
@@ -39,9 +39,28 @@ struct optee_shm_arg_entry {
 	DECLARE_BITMAP(map, MAX_ARG_COUNT_PER_ENTRY);
 };
 
+void optee_cq_init(struct optee_call_queue *cq, int thread_count)
+{
+	mutex_init(&cq->mutex);
+	INIT_LIST_HEAD(&cq->normal_waiters);
+	INIT_LIST_HEAD(&cq->sys_waiters);
+	/*
+	 * If cq->total_thread_count is 0 then we're not trying to keep
+	 * track of how many free threads we have, instead we're relying on
+	 * the secure world to tell us when we're out of thread and have to
+	 * wait for another thread to become available.
+	 */
+	cq->total_thread_count = thread_count;
+	cq->free_normal_thread_count = thread_count;
+}
+
 void optee_cq_wait_init(struct optee_call_queue *cq,
 			struct optee_call_waiter *w, bool sys_thread)
 {
+	bool need_wait = false;
+
+	memset(w, 0, sizeof(*w));
+
 	/*
 	 * We're preparing to make a call to secure world. In case we can't
 	 * allocate a thread in secure world we'll end up waiting in
@@ -53,15 +72,46 @@ void optee_cq_wait_init(struct optee_call_queue *cq,
 	mutex_lock(&cq->mutex);
 
 	/*
-	 * We add ourselves to the queue, but we don't wait. This
-	 * guarantees that we don't lose a completion if secure world
-	 * returns busy and another thread just exited and try to complete
-	 * someone.
+	 * We add ourselves to a queue, but we don't wait. This guarantees
+	 * that we don't lose a completion if secure world returns busy and
+	 * another thread just exited and try to complete someone.
 	 */
 	init_completion(&w->c);
-	list_add_tail(&w->list_node, &cq->waiters);
+	w->sys_thread_req = sys_thread;
+	if (sys_thread) {
+		list_add_tail(&w->list_node, &cq->sys_waiters);
+		if (cq->sys_thread_in_use) {
+			need_wait = true;
+		} else {
+			cq->sys_thread_in_use = true;
+			w->sys_thread_used = true;
+		}
+	} else {
+		list_add_tail(&w->list_node, &cq->normal_waiters);
+		if (cq->total_thread_count) {
+			/*
+			 * Claim a normal thread if one is available, else
+			 * we'll need to wait for a normal thread to be
+			 * released.
+			 */
+			if (cq->free_normal_thread_count > 0)
+				cq->free_normal_thread_count--;
+			else
+				need_wait = true;
+		}
+	}
 
 	mutex_unlock(&cq->mutex);
+
+	while (need_wait) {
+		optee_cq_wait_for_completion(cq, w);
+		mutex_lock(&cq->mutex);
+		if (cq->free_normal_thread_count > 0) {
+			cq->free_normal_thread_count--;
+			need_wait = false;
+		}
+		mutex_unlock(&cq->mutex);
+	}
 }
 
 void optee_cq_wait_for_completion(struct optee_call_queue *cq,
@@ -74,7 +124,10 @@ void optee_cq_wait_for_completion(struct optee_call_queue *cq,
 	/* Move to end of list to get out of the way for other waiters */
 	list_del(&w->list_node);
 	reinit_completion(&w->c);
-	list_add_tail(&w->list_node, &cq->waiters);
+	if (w->sys_thread_req)
+		list_add_tail(&w->list_node, &cq->sys_waiters);
+	else
+		list_add_tail(&w->list_node, &cq->normal_waiters);
 
 	mutex_unlock(&cq->mutex);
 }
@@ -83,10 +136,19 @@ static void optee_cq_complete_one(struct optee_call_queue *cq)
 {
 	struct optee_call_waiter *w;
 
-	list_for_each_entry(w, &cq->waiters, list_node) {
+	list_for_each_entry(w, &cq->sys_waiters, list_node) {
 		if (!completion_done(&w->c)) {
 			complete(&w->c);
-			break;
+			return;
+		}
+	}
+
+	if (!cq->total_thread_count || cq->free_normal_thread_count > 0) {
+		list_for_each_entry(w, &cq->normal_waiters, list_node) {
+			if (!completion_done(&w->c)) {
+				complete(&w->c);
+				break;
+			}
 		}
 	}
 }
@@ -104,6 +166,11 @@ void optee_cq_wait_final(struct optee_call_queue *cq,
 	/* Get out of the list */
 	list_del(&w->list_node);
 
+	if (w->sys_thread_used)
+		cq->sys_thread_in_use = false;
+	else
+		cq->free_normal_thread_count++; /* Release a normal thread */
+
 	/* Wake up one eventual waiting task */
 	optee_cq_complete_one(cq);
 
@@ -119,6 +186,31 @@ void optee_cq_wait_final(struct optee_call_queue *cq,
 	mutex_unlock(&cq->mutex);
 }
 
+bool optee_cq_inc_sys_thread_count(struct optee_call_queue *cq)
+{
+	if (cq->total_thread_count <= 1)
+		return false;
+
+	mutex_lock(&cq->mutex);
+	if (!cq->sys_thread_req_count)
+		cq->free_normal_thread_count--;
+	cq->sys_thread_req_count++;
+	mutex_unlock(&cq->mutex);
+
+	return true;
+}
+
+void optee_cq_dec_sys_thread_count(struct optee_call_queue *cq)
+{
+	mutex_lock(&cq->mutex);
+	cq->sys_thread_req_count--;
+	if (!cq->sys_thread_req_count)
+		cq->free_normal_thread_count++;
+	/* If there's someone waiting, let it resume */
+	optee_cq_complete_one(cq);
+	mutex_unlock(&cq->mutex);
+}
+
 /* Requires the filpstate mutex to be held */
 static struct optee_session *find_session(struct optee_context_data *ctxdata,
 					  u32 session_id)
@@ -361,6 +453,27 @@ int optee_open_session(struct tee_context *ctx,
 	return rc;
 }
 
+int optee_system_session(struct tee_context *ctx, u32 session)
+{
+	struct optee_context_data *ctxdata = ctx->data;
+	struct optee *optee = tee_get_drvdata(ctx->teedev);
+	struct optee_session *sess;
+	int rc = -EINVAL;
+
+	mutex_lock(&ctxdata->mutex);
+
+	sess = find_session(ctxdata, session);
+	if (sess && !sess->use_sys_thread &&
+	    optee_cq_inc_sys_thread_count(&optee->call_queue)) {
+		rc = 0;
+		sess->use_sys_thread = true;
+	}
+
+	mutex_unlock(&ctxdata->mutex);
+
+	return rc;
+}
+
 int optee_close_session_helper(struct tee_context *ctx, u32 session,
 			       bool system_thread)
 {
@@ -378,6 +491,8 @@ int optee_close_session_helper(struct tee_context *ctx, u32 session,
 	msg_arg->session = session;
 	optee->ops->do_call_with_arg(ctx, shm, offs, system_thread);
 
+	if (system_thread)
+		optee_cq_dec_sys_thread_count(&optee->call_queue);
 	optee_free_msg_arg(ctx, entry, offs);
 
 	return 0;
diff --git a/drivers/tee/optee/ffa_abi.c b/drivers/tee/optee/ffa_abi.c
index 5fde9d4100e3..0c9055691343 100644
--- a/drivers/tee/optee/ffa_abi.c
+++ b/drivers/tee/optee/ffa_abi.c
@@ -852,8 +852,7 @@ static int optee_ffa_probe(struct ffa_device *ffa_dev)
 	if (rc)
 		goto err_unreg_supp_teedev;
 	mutex_init(&optee->ffa.mutex);
-	mutex_init(&optee->call_queue.mutex);
-	INIT_LIST_HEAD(&optee->call_queue.waiters);
+	optee_cq_init(&optee->call_queue, 0);
 	optee_supp_init(&optee->supp);
 	optee_shm_arg_cache_init(optee, arg_cache_flags);
 	ffa_dev_set_drvdata(ffa_dev, optee);
diff --git a/drivers/tee/optee/optee_private.h b/drivers/tee/optee/optee_private.h
index b68273051454..b8f22d7b34a6 100644
--- a/drivers/tee/optee/optee_private.h
+++ b/drivers/tee/optee/optee_private.h
@@ -40,15 +40,39 @@ typedef void (optee_invoke_fn)(unsigned long, unsigned long, unsigned long,
 				unsigned long, unsigned long,
 				struct arm_smccc_res *);
 
+/*
+ * struct optee_call_waiter - TEE entry may need to wait for a free TEE thread
+ * @list_node		Reference in waiters list
+ * @c			Waiting completion reference
+ * @sys_thread_req	True only if waiter belongs to a requested system thread
+ * @sys_thread_used	True only if waiter is consuming the system thread
+ */
 struct optee_call_waiter {
 	struct list_head list_node;
 	struct completion c;
+	bool sys_thread_req;
+	bool sys_thread_used;
 };
 
+/*
+ * struct optee_call_queue - OP-TEE call queue management
+ * @mutex			Serializes access to this struct
+ * @normal_waiters		List of normal threads waiting to enter OP-TEE
+ * @sys_waiters			List of system threads waiting to enter OP-TEE
+ * @total_thread_count		Overall number of thread context in OP-TEE or 0
+ * @free_normal_thread_count	Number of normal threads context free in OP-TEE
+ * @sys_thread_req_count	Number of registered system thread requests
+ * @sys_thread_in_use		True only if reserved system entry is consumed
+ */
 struct optee_call_queue {
 	/* Serializes access to this struct */
 	struct mutex mutex;
-	struct list_head waiters;
+	struct list_head normal_waiters;
+	struct list_head sys_waiters;
+	int total_thread_count;
+	int free_normal_thread_count;
+	int sys_thread_req_count;
+	bool sys_thread_in_use;
 };
 
 struct optee_notif {
@@ -254,6 +278,7 @@ int optee_supp_send(struct tee_context *ctx, u32 ret, u32 num_params,
 int optee_open_session(struct tee_context *ctx,
 		       struct tee_ioctl_open_session_arg *arg,
 		       struct tee_param *param);
+int optee_system_session(struct tee_context *ctx, u32 session);
 int optee_close_session_helper(struct tee_context *ctx, u32 session,
 			       bool system_thread);
 int optee_close_session(struct tee_context *ctx, u32 session);
@@ -303,6 +328,9 @@ static inline void optee_to_msg_param_value(struct optee_msg_param *mp,
 	mp->u.value.c = p->u.value.c;
 }
 
+void optee_cq_init(struct optee_call_queue *cq, int thread_count);
+bool optee_cq_inc_sys_thread_count(struct optee_call_queue *cq);
+void optee_cq_dec_sys_thread_count(struct optee_call_queue *cq);
 void optee_cq_wait_init(struct optee_call_queue *cq,
 			struct optee_call_waiter *w, bool sys_thread);
 void optee_cq_wait_for_completion(struct optee_call_queue *cq,
diff --git a/drivers/tee/optee/smc_abi.c b/drivers/tee/optee/smc_abi.c
index e2763cdcf111..3314ffeb91c8 100644
--- a/drivers/tee/optee/smc_abi.c
+++ b/drivers/tee/optee/smc_abi.c
@@ -1209,6 +1209,7 @@ static const struct tee_driver_ops optee_clnt_ops = {
 	.release = optee_release,
 	.open_session = optee_open_session,
 	.close_session = optee_close_session,
+	.system_session = optee_system_session,
 	.invoke_func = optee_invoke_func,
 	.cancel_req = optee_cancel_req,
 	.shm_register = optee_shm_register,
@@ -1356,6 +1357,16 @@ static bool optee_msg_exchange_capabilities(optee_invoke_fn *invoke_fn,
 	return true;
 }
 
+static unsigned int optee_msg_get_thread_count(optee_invoke_fn *invoke_fn)
+{
+	struct arm_smccc_res res;
+
+	invoke_fn(OPTEE_SMC_GET_THREAD_COUNT, 0, 0, 0, 0, 0, 0, 0, &res);
+	if (res.a0)
+		return 0;
+	return res.a1;
+}
+
 static struct tee_shm_pool *
 optee_config_shm_memremap(optee_invoke_fn *invoke_fn, void **memremaped_shm)
 {
@@ -1609,6 +1620,7 @@ static int optee_probe(struct platform_device *pdev)
 	struct optee *optee = NULL;
 	void *memremaped_shm = NULL;
 	unsigned int rpc_param_count;
+	unsigned int thread_count;
 	struct tee_device *teedev;
 	struct tee_context *ctx;
 	u32 max_notif_value;
@@ -1636,6 +1648,7 @@ static int optee_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
+	thread_count = optee_msg_get_thread_count(invoke_fn);
 	if (!optee_msg_exchange_capabilities(invoke_fn, &sec_caps,
 					     &max_notif_value,
 					     &rpc_param_count)) {
@@ -1725,8 +1738,7 @@ static int optee_probe(struct platform_device *pdev)
 	if (rc)
 		goto err_unreg_supp_teedev;
 
-	mutex_init(&optee->call_queue.mutex);
-	INIT_LIST_HEAD(&optee->call_queue.waiters);
+	optee_cq_init(&optee->call_queue, thread_count);
 	optee_supp_init(&optee->supp);
 	optee->smc.memremaped_shm = memremaped_shm;
 	optee->pool = pool;
-- 
2.25.1