On Thu, 13 Feb 2025 12:11:52 +0530 Sumit Garg <sumit.garg@xxxxxxxxxx> wrote: > Hi Boris, > > On Thu, 13 Feb 2025 at 01:26, Boris Brezillon > <boris.brezillon@xxxxxxxxxxxxx> wrote: > > > > +Florent, who's working on protected-mode support in Panthor. > > > > Hi Jens, > > > > On Tue, 17 Dec 2024 11:07:36 +0100 > > Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote: > > > > > Hi, > > > > > > This patch set allocates the restricted DMA-bufs via the TEE subsystem. > > > > We're currently working on protected-mode support for Panthor [1] and it > > looks like your series (and the OP-TEE implementation that goes with > > it) would allow us to have a fully upstream/open solution for the > > protected content use case we're trying to support. I need a bit more > > time to play with the implementation but this looks very promising > > (especially the lend rstmem feature, which might help us allocate our > > FW sections that are supposed to execute code accessing protected > > content). > > Glad to hear that, if you can demonstrate an open source use case > based on this series then it will help to land it. We really would > love to see support for restricted DMA-buf consumers be it GPU, crypto > accelerator, media pipeline etc. > > > > > > > > > The TEE subsystem handles the DMA-buf allocations since it is the TEE > > > (OP-TEE, AMD-TEE, TS-TEE, or perhaps a future QCOMTEE) which sets up the > > > restrictions for the memory used for the DMA-bufs. > > > > > > I've added a new IOCTL, TEE_IOC_RSTMEM_ALLOC, to allocate the restricted > > > DMA-bufs. This IOCTL reaches the backend TEE driver, allowing it to choose > > > how to allocate the restricted physical memory. > > > > I'll probably have more questions soon, but here's one to start: any > > particular reason you didn't go for a dma-heap to expose restricted > > buffer allocation to userspace? I see you already have a cdev you can > > take ioctl()s from, but my understanding was that dma-heap was the > > standard solution for these device-agnostic/central allocators. > > This series started with the DMA heap approach only here [1] but later > discussions [2] lead us here. To point out specifically: > > - DMA heaps require reliance on DT to discover static restricted > regions carve-outs whereas via the TEE implementation driver (eg. > OP-TEE) those can be discovered dynamically. Hm, the system heap [1] doesn't rely on any DT information AFAICT. The dynamic allocation scheme, where the TEE implementation allocates a chunk of protected memory for us would have a similar behavior, I guess. > - Dynamic allocation of buffers and making them restricted requires > vendor specific driver hooks with DMA heaps whereas the TEE subsystem > abstracts that out with underlying TEE implementation (eg. OP-TEE) > managing the dynamic buffer restriction. Yeah, the lend rstmem feature is clearly something tee specific, and I think that's okay to assume the user knows the protection request should go through the tee subsystem in that case. > - TEE subsystem already has a well defined user-space interface for > managing shared memory buffers with TEE and restricted DMA buffers > will be yet another interface managed along similar lines. Okay, so the very reason I'm asking about the dma-buf heap interface is because there might be cases where the protected/restricted allocation doesn't go through the TEE (Mediatek has a TEE-free implementation for instance, but I realize vendor implementations are probably not the best selling point :-/). If we expose things as a dma-heap, we have a solution where integrators can pick the dma-heap they think is relevant for protected buffer allocations without the various drivers (GPU, video codec, ...) having to implement a dispatch function for all possible implementations. The same goes for userspace allocations, where passing a dma-heap name, is simpler than supporting different ioctl()s based on the allocation backend. [1]https://elixir.bootlin.com/linux/v6.13.2/source/drivers/dma-buf/heaps/system_heap.c#L424
