Hi Jens, On Thu, 10 Jun 2021 at 12:48, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote: > > On Wed, Jun 09, 2021 at 04:22:49PM +0530, Sumit Garg wrote: > > + Rijo > > > > On Wed, 9 Jun 2021 at 11:16, Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> wrote: > [snip] > > > > > - tee_shm_alloc() performs allocations using contiguous pages > > > from alloc_pages() while tee_shm_register() performs non-contiguous > > > allocations with kcalloc(). I suspect this would be fine but I don't > > > know the secure world side of these things well enough to assess the > > > risk involved with such a change on the kernel side. > > > > > > > I don't think that would make any difference. > > Agree. > > > > > > I should have mentioned this in the cover letter but my hope was that > > > these minimal changes would be accepted and then additional work could > > > be done to merge tee_shm_alloc() and tee_shm_register() in a way that > > > would allow the caller to request contiguous or non-contiguous pages, > > > fix up the additional issues mentioned above, and then adjust the > > > call sites in ftpm and tee_bnxt_fw as appropriate. > > > > > > I think that's a bigger set of changes because there are several things > > > that still confuse/concern me: > > > > > > - Why does tee_shm_alloc() use TEE_SHM_MAPPED while tee_shm_register() > > > uses TEE_SHM_KERNEL_MAPPED or TEE_SHM_USER_MAPPED? Why do all three > > > exist? > > > > 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 had another approach in mind in "[PATCH 0/7] tee: shared memory updates", > https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@xxxxxxxxxx/ > > The flags needed by tee_shm_alloc() and tee_shm_register() aren't > very intuitive and in fact only accept quite few combinations. So my > idea was to hide those flags from callers outside of the TEE subsystem > with tee_shm_alloc_kernel_buf(). > That looks like a good idea to hide flags from users. BTW, my only objection earlier with Tyler's and your patch-set is the usage of TEE_SHM_REGISTER flag in generic TEE methods: tee_shm_alloc*. AFAIU, the only reason for such an additional flag is in case of OP-TEE only because the OP-TEE driver could implement allocated shared memory via re-using dynamic shared memory approach as well. And that additional flag is only needed to differentiate that OP-TEE driver's private memory shouldn't be registered with OP-TEE. If this understanding is correct then we should introduce a separate flag as TEE_SHM_PRIV that should only be set inside tee_shm_alloc_anon_kernel_buf(). As otherwise passing TEE_SHM_REGISTER flag for shared memory alloc API for other TEEs like AMD-TEE etc. would be useless. > The approach with tee_shm_register() you suggest above has the drawback > that the TEE driver is forced to be able to handle any kernel memory. That's the value-add in the problem that Tyler is trying to resolve that driver should be able to free up the memory as needed as a private buffer. > This is OK with OP-TEE and dynamic shared memory enabled, but there are > platforms where dynamic shared memory isn't enabled. In those case must > the memory be allocated from a special pool. Is there any limitation for those platforms to not support dynamic shared memory in OP-TEE? If there isn't then we should able to handle this via match for TEE_GEN_CAP_REG_MEM in the ftpm_tee_match() and optee_ctx_match() APIs. > > Do you see any problem with instead replacing tee_shm_alloc() > with tee_shm_alloc_kernel_buf()? I don't see any problems apart from one mentioned above. -Sumit > > Cheers, > Jens
