AFAIK, its due the the inherent nature of tee_shm_alloc() and tee_shm_register() where tee_shm_alloc() doesn't need to know whether its a kernel or user-space memory since it is the one that allocates whereas tee_shm_register() need to know that since it has to register pre-allocated client memory.
- Why does tee_shm_register() unconditionally use non-contiguous
allocations without ever taking into account whether or not OPTEE_SMC_SEC_CAP_DYNAMIC_SHM was set? It sounds like that's required from my reading of https://optee.readthedocs.io/en/latest/architecture/core.html#noncontiguous-....
Yeah, but do we have platforms in OP-TEE that don't support dynamic shared memory? I guess it has become the sane default which is a mandatory requirement when it comes to OP-TEE driver in u-boot.
- Why is TEE_SHM_REGISTER implemented at the TEE driver level when it is
specific to OP-TEE? How to better abstract that away?
I would like you to go through Section "3.2.4. Shared Memory" in TEE Client API Specification. There are two standard ways for shared memory approach with TEE:
- A Shared Memory block can either be existing Client Application
memory (kernel driver in our case) which is subsequently registered with the TEE Client API (using tee_shm_register() in our case).
- Or memory which is allocated on behalf of the Client Application
using the TEE Client API (using tee_shm_alloc() in our case).
Let me know if you agree with the more minimal approach that I took for these bug fix series or still feel like tee_shm_register() should be fixed up so that it is usable. Thanks!
From drivers perspective I think the change should be:
tee_shm_alloc()
to
kcalloc() tee_shm_register()
I've just posted "[PATCH 0/7] tee: shared memory updates", https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@linaro....
Where tee_shm_alloc() is replaced by among other functions tee_shm_alloc_kernel_buf(). tee_shm_alloc_kernel_buf() takes care of the problem with TEE_SHM_DMA_BUF.
Thanks Jens. The series looks fine. Tested too.
- Allen