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Then, catch cases where the low-level TSM driver tries to use ID > 255. This is on the assumption that most implementations will allocate > starting from zero. > >>>>>> And then what are we doing to do when we start adding link streams? I >>>>>> suggest decoupling pci_ide::stream_id from stream_id in sel_ide_offset() >>>>>> (which is more like selective_stream_index) from the start. >>>>> >>>>> Setting aside that I agree with you that Stream index be separated from >>>>> from Stream ID, what would motivate Linux to consider setting up Link >>>>> Stream IDE? >>>>> >>>>> One of the operational criticisms of Link IDE is that it requires adding >>>>> more points of failure into the TCB where a compromised switch can snoop >>>>> traffic. It also adds more Keys and their associated maintainenace >>>>> overhead. So, before we start planning ahead for Link IDE and Selective >>>>> Stream IDE to co-exist in the implementation, I think we need a clear >>>>> use case that demonstrates Link IDE is going to graduate from the >>>>> specification into practical deployments. >>>> >>>> Probably for things like CXL which connect directly to the soc? I do not >>>> really know, I only touch link streams because of that only device which >>>> is like to see the light of the day though. >>> >>> CXL TSP is a wholly separate operation model and it expects that CXL >>> devices, and more specifically CXL memory, are inside the TCB before the >>> OS boots. So there is no current need for Linux to consider Link IDE for >>> CXL. >> >> Link IDE or any IDE? I know very little about CXL but some of those >> device types are not just simple fast memory but also do read/write >> from/to that memory so they cannot rely on CPU memory encryption and IDE >> makes sense for those (especially Link IDE as there are no bridges, or >> are there?). Thanks, > > So there are 2 use cases CXL.cache and CXL.mem, and of CXL.mem there is > general memory expansion and accelerator memory. Most of the devices in > the market and the sole focus of the CXL TSP (TEE Security Protocol) > specification is how to get CXL.mem from general memory expansion > devices (Type-3) into the TCB. From the spec: (self educating now) So CXL.io is not a thing, or not going to support TSP? Wiki mentions IO registers and DMA, not relevant here why? Thanks, > > "This CXL security content scope focuses on features that are needed for > confidential computing utilizing CXL Type 3 memory expander devices" > > The TSP definition specifies that CXL.mem memory is brought into the TCB > by pre-OS software. > > It goes on to say, "Transport security is optional for TSP", i.e. IDE is > optional. If you have initiator based memory encryption then you do not > also need encryption on the transport. > > So, IDE is optional and any optional IDE establishment will be by pre-OS > software. There is nothing I can see from CXL-land threatening to make > the Linux IDE implementation care about Link IDE. -- Alexey