Re: [PATCH v10 3/4] tee: optee: support tracking system threads

[Etienne CARRIERE - foss]

> From: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Sent: Friday, October 6, 2023 11:33 AM
> 
> On Tue, 3 Oct 2023 at 19:36, Etienne Carriere
> <etienne.carriere@xxxxxxxxxxx> wrote:
> >
> > 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 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.
> 
> How would that be possible? The system thread wakeup
> (free_thread_threshold = 0) is given priority over normal thread
> wakeup (free_thread_threshold = 1). I think a single queue list would
> be sufficient as demonstrated in v9.
> 

Hello Sumit,

I think a system session can be trapped waiting when using a single queue list.
To have a chance to reach the TEE, a waiting thread must wait that a TEE thread comes out of the TEE and calls complete() on the waitqueue to wake next waiter.

To illustrate, consider a 10 TEE threads configuration on TEE side (::total_thread_count=10 at init),
and several TEE clients in Linux OS, including 2 system sessions, from 2 consumer drivers (::sys_thread_req_count=2).

Imagine the 9 normal threads and the 1 system thread are in use. (::free_thread_count=0),
Now comes the other system session: it goes to the waitqueue list.
Now comes a normal session invocation: it goes to the waitqueue list, 1st position.

Now, TEE system thread returns to Linux:
It increments the counter, ::free_thread_count=1, and calls complete() for the waitequeue.
The 1st element in the waitqueue list is the last entered normal session invocation.
However, that waiter won't switch local boolean 'need_wait'  to false because ::free_thread_count=1 and ::sys_thread_req_count!=0.
So no attempt to reach TEE and wake another waiter on return.
At that point there is a system session in the waitqueue list that could enter TEE (::free_thread_count=1) but is waiting someone returns from the TEE.

With 2 lists, we first treat system sessions to overcome that.
Am I missing something?

Best regards,
Etienne

> -Sumit
> 
> > - 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          | 128 ++++++++++++++++++++++++++++--
> >  drivers/tee/optee/ffa_abi.c       |   3 +-
> >  drivers/tee/optee/optee_private.h |  24 +++++-
> >  drivers/tee/optee/smc_abi.c       |  16 +++-
> >  4 files changed, 159 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c
> > index 152ae9bb1785..38543538d77b 100644
> > --- a/drivers/tee/optee/call.c
> > +++ b/drivers/tee/optee/call.c
> > @@ -39,9 +39,31 @@ 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->sys_waiters);
> > +       INIT_LIST_HEAD(&cq->normal_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));
> > +       w->sys_thread = sys_thread;
> > +
> >         /*
> >          * 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 +75,47 @@ 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);
> > +
> > +       if (sys_thread)
> > +               list_add_tail(&w->list_node, &cq->sys_waiters);
> > +       else
> > +               list_add_tail(&w->list_node, &cq->normal_waiters);
> > +
> > +       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,
> > @@ -74,7 +128,11 @@ 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)
> > +               list_add_tail(&w->list_node, &cq->sys_waiters);
> > +       else
> > +               list_add_tail(&w->list_node, &cq->normal_waiters);
> >
> >         mutex_unlock(&cq->mutex);
> >  }
> > @@ -83,7 +141,15 @@ 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) {
> > +       /* Wake waiting system session first */
> > +       list_for_each_entry(w, &cq->sys_waiters, list_node) {
> > +               if (!completion_done(&w->c)) {
> > +                       complete(&w->c);
> > +                       break;
> > +               }
> > +       }
> > +
> > +       list_for_each_entry(w, &cq->normal_waiters, list_node) {
> >                 if (!completion_done(&w->c)) {
> >                         complete(&w->c);
> >                         break;
> > @@ -104,6 +170,8 @@ 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 +187,28 @@ 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 +451,27 @@ 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 +491,9 @@ 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 b68273051454..69f6397c3646 100644
> > --- a/drivers/tee/optee/optee_private.h
> > +++ b/drivers/tee/optee/optee_private.h
> > @@ -40,15 +40,35 @@ 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
> > + * @sys_waiters                        List of system threads waiting to enter OP-TEE
> > + * @normal_waiters             List of normal 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;
> > +       struct list_head sys_waiters;
> > +       struct list_head normal_waiters;
> > +       int total_thread_count;
> > +       int free_thread_count;
> > +       int sys_thread_req_count;
> >  };
> >
> >  struct optee_notif {
> > @@ -254,6 +274,7 @@ 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 +324,7 @@ 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
> >
>