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

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Date:   Thu, 10 Jun 2021 13:10:35 +0530
From:   Allen Pais <apais@...ux.microsoft.com>
To:     Jens Wiklander <jens.wiklander@...aro.org>
Cc:     Sumit Garg <sumit.garg@...aro.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Rijo-john.Thomas@....com, Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Vikas Gupta <vikas.gupta@...adcom.com>,
        Thirupathaiah Annapureddy <thiruan@...rosoft.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Rafał Miłecki <zajec5@...il.com>,
        OP-TEE TrustedFirmware <op-tee@...ts.trustedfirmware.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com, linux-mips@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf
 backing

>> 
>> 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