[PATCH v11 3/4] tee: optee: support tracking system threads

From: Etienne Carriere
Date: Mon Oct 16 2023 - 05:05:03 EST

Adds support in the OP-TEE driver to keep track of reserved system
threads. The logic allows one OP-TEE thread to be reserved to TEE system
sessions.

The optee_cq_*() functions are updated to handle this if enabled,
that is when TEE describes how many thread context it supports
and when at least 1 session has registered as a system session
(using tee_client_system_session()).

For sake of simplicity, initialization of call queue management
is factorized into new helper function optee_cq_init().

The SMC ABI part of the driver enables this tracking, but the
FF-A ABI part does not.

Co-developed-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
Co-developed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
Signed-off-by: Etienne Carriere <etienne.carriere@xxxxxxxxxxx>
---
Changes since v10:
- Use a single list instead of 2 and wake system session first from
that list in optee_cq_complete_one().

Changes since v9:
- Add a reference counter for TEE system thread provisioning. We reserve
a TEE thread context for system session only when there is at least
1 opened system session.
- Use 2 wait queue lists, normal_waiters and sys_waiter, as proposed in
patch v8. Using a single list can prevent a waiting system thread from
being resumed if the executing system thread wakes a normal waiter in
the list.
- Updated my e-mail address.
- Rephrased a bit the commit message.

Changes since patch v8
- Patch v9 (reference below) attempted to simplify the implementation
https://lore.kernel.org/lkml/20230517143311.585080-1-sumit.garg@xxxxxxxxxx/#t

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 | 106 ++++++++++++++++++++++++++++++
drivers/tee/optee/ffa_abi.c | 3 +-
drivers/tee/optee/optee_private.h | 20 ++++++
drivers/tee/optee/smc_abi.c | 16 ++++-
4 files changed, 141 insertions(+), 4 deletions(-)

diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c
index 152ae9bb1785..b04c49c69619 100644
--- a/drivers/tee/optee/call.c
+++ b/drivers/tee/optee/call.c
@@ -39,9 +39,29 @@ 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->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_thread_count = thread_count;
+}
+
void optee_cq_wait_init(struct optee_call_queue *cq,
struct optee_call_waiter *w, bool sys_thread)
{
+ unsigned int free_thread_threshold;
+ 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
@@ -60,8 +80,38 @@ void optee_cq_wait_init(struct optee_call_queue *cq,
*/
init_completion(&w->c);
list_add_tail(&w->list_node, &cq->waiters);
+ w->sys_thread = sys_thread;
+
+ if (cq->total_thread_count) {
+ if (sys_thread || !cq->sys_thread_req_count)
+ free_thread_threshold = 0;
+ else
+ free_thread_threshold = 1;
+
+ if (cq->free_thread_count > free_thread_threshold)
+ cq->free_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 (sys_thread || !cq->sys_thread_req_count)
+ free_thread_threshold = 0;
+ else
+ free_thread_threshold = 1;
+
+ if (cq->free_thread_count > free_thread_threshold) {
+ cq->free_thread_count--;
+ need_wait = false;
+ }
+
+ mutex_unlock(&cq->mutex);
+ }
}

void optee_cq_wait_for_completion(struct optee_call_queue *cq,
@@ -83,6 +133,14 @@ static void optee_cq_complete_one(struct optee_call_queue *cq)
{
struct optee_call_waiter *w;

+ /* Wake a waiting system session if any, prior to a normal session */
+ list_for_each_entry(w, &cq->waiters, list_node) {
+ if (w->sys_thread && !completion_done(&w->c)) {
+ complete(&w->c);
+ return;
+ }
+ }
+
list_for_each_entry(w, &cq->waiters, list_node) {
if (!completion_done(&w->c)) {
complete(&w->c);
@@ -104,6 +162,8 @@ void optee_cq_wait_final(struct optee_call_queue *cq,
/* Get out of the list */
list_del(&w->list_node);

+ cq->free_thread_count++;
+
/* Wake up one eventual waiting task */
optee_cq_complete_one(cq);

@@ -119,6 +179,28 @@ void optee_cq_wait_final(struct optee_call_queue *cq,
mutex_unlock(&cq->mutex);
}

+/* Count registered system sessions to reserved a system thread or not */
+static bool optee_cq_incr_sys_thread_count(struct optee_call_queue *cq)
+{
+ if (cq->total_thread_count <= 1)
+ return false;
+
+ mutex_lock(&cq->mutex);
+ cq->sys_thread_req_count++;
+ mutex_unlock(&cq->mutex);
+
+ return true;
+}
+
+static void optee_cq_decr_sys_thread_count(struct optee_call_queue *cq)
+{
+ mutex_lock(&cq->mutex);
+ cq->sys_thread_req_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 +443,27 @@ int optee_open_session(struct tee_context *ctx,
return rc;
}

+int optee_system_session(struct tee_context *ctx, u32 session)
+{
+ struct optee *optee = tee_get_drvdata(ctx->teedev);
+ struct optee_context_data *ctxdata = ctx->data;
+ struct optee_session *sess;
+ int rc = -EINVAL;
+
+ mutex_lock(&ctxdata->mutex);
+
+ sess = find_session(ctxdata, session);
+ if (sess && (sess->use_sys_thread ||
+ optee_cq_incr_sys_thread_count(&optee->call_queue))) {
+ sess->use_sys_thread = true;
+ rc = 0;
+ }
+
+ mutex_unlock(&ctxdata->mutex);
+
+ return rc;
+}
+
int optee_close_session_helper(struct tee_context *ctx, u32 session,
bool system_thread)
{
@@ -380,6 +483,9 @@ int optee_close_session_helper(struct tee_context *ctx, u32 session,

optee_free_msg_arg(ctx, entry, offs);

+ if (system_thread)
+ optee_cq_decr_sys_thread_count(&optee->call_queue);
+
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 b659a6f521df..8e944e611b66 100644
--- a/drivers/tee/optee/optee_private.h
+++ b/drivers/tee/optee/optee_private.h
@@ -40,15 +40,33 @@ 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 if waiter belongs to a system thread
+ */
struct optee_call_waiter {
struct list_head list_node;
struct completion c;
+ bool sys_thread;
};

+/*
+ * struct optee_call_queue - OP-TEE call queue management
+ * @mutex Serializes access to this struct
+ * @waiters List of threads waiting to enter OP-TEE
+ * @total_thread_count Overall number of thread context in OP-TEE or 0
+ * @free_thread_count Number of threads context free in OP-TEE
+ * @sys_thread_req_count Number of registered system thread sessions
+ */
struct optee_call_queue {
/* Serializes access to this struct */
struct mutex mutex;
struct list_head waiters;
+ int total_thread_count;
+ int free_thread_count;
+ int sys_thread_req_count;
};

struct optee_notif {
@@ -252,6 +270,7 @@ 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);
@@ -301,6 +320,7 @@ 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);
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 1033d7da03ea..5595028d6dae 100644
--- a/drivers/tee/optee/smc_abi.c
+++ b/drivers/tee/optee/smc_abi.c
@@ -1211,6 +1211,7 @@ 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,
@@ -1358,6 +1359,16 @@ 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)
{
@@ -1610,6 +1621,7 @@ 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;
@@ -1637,6 +1649,7 @@ 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)) {
@@ -1726,8 +1739,7 @@ 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