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I just love the AMD mails servers :( Christian. Am 15.01.25 um 14:45 schrieb Christian König: > Am 15.01.25 um 14:38 schrieb Jason Gunthorpe: >> On Wed, Jan 15, 2025 at 10:38:00AM +0100, Christian König wrote: >>> Am 10.01.25 um 21:54 schrieb Jason Gunthorpe: >>>> [SNIP] >>>>>> I don't fully understand your use case, but I think it's quite likely >>>>>> that we already have that working. >>>> In Intel CC systems you cannot mmap secure memory or the system will >>>> take a machine check. >>>> >>>> You have to convey secure memory inside a FD entirely within the >>>> kernel so that only an importer that understands how to handle secure >>>> memory (such as KVM) is using it to avoid machine checking. >>>> >>>> The patch series here should be thought of as the first part of this, >>>> allowing PFNs to flow without VMAs. IMHO the second part of preventing >>>> machine checks is not complete. >>>> >>>> In the approach I have been talking about the secure memory would be >>>> represented by a p2p_provider structure that is incompatible with >>>> everything else. For instance importers that can only do DMA would >>>> simply cleanly fail when presented with this memory. >>> That's a rather interesting use case, but not something I consider fitting >>> for the DMA-buf interface. >> To recast the problem statement, it is basically the same as your >> device private interconnects. There are certain devices that >> understand how to use this memory, and if they work together they can >> access it. >> >>> See DMA-buf in meant to be used between drivers to allow DMA access on >>> shared buffers. >> They are shared, just not with everyone :) >> >>> What you try to do here instead is to give memory in the form of a file >>> descriptor to a client VM to do things like CPU mapping and giving it to >>> drivers to do DMA etc... >> How is this paragraph different from the first? It is a shared buffer >> that we want real DMA and CPU "DMA" access to. It is "private" so >> things that don't understand the interconnect rules cannot access it. > > Yeah, but it's private to the exporter. And a very fundamental rule of > DMA-buf is that the exporter is the one in control of things. > > So for example it is illegal for an importer to setup CPU mappings to > a buffer. That's why we have dma_buf_mmap() which redirects mmap() > requests from the importer to the exporter. > > In your use case here the importer wants to be in control and do > things like both CPU as well as DMA mappings. > > As far as I can see that is really not an use case which fits DMA-buf > in any way. > >>> That sounds more something for the TEE driver instead of anything DMA-buf >>> should be dealing with. >> Has nothing to do with TEE. > > Why? > > Regards, > Christian. > >> Jason >