Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf backing

Allen Pais
2021-06-10T07:40:44Z

>>
>> 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-shared-buffers.
>>
>> 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:
>>
>> 1. 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).
>>
>> 2. 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.org/
>
> 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