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The fixes ensure >>>>>>> sgt mapping is correct, and proper for large MMIO regions. >>>>>>> >>>>>>> Patch 1 fixes a silent integer overflow for mapping length exceeding 4G >>>>>>> (Previously submitted as [PATCH v7] dma-buf: Fix silent overflow for >>>>>>> phys vec to sgt) >>>>>>> https://lore.kernel.org/all/20260609164047.486227-1-xuehaohu@google.com/ >>>>>>> >>>>>>> Patch 2 Splits sgl by largest page aligned chunk >>>>>>> (Previously submitted as [PATCH v3] dma-buf: Split sgl by largest page-aligned chunk) >>>>>>> https://lore.kernel.org/all/20260722233806.3922093-1-dhu@x6u.co/ >>>>>> >>>>>> *sigh* such issues are exactly the reason why I didn't wanted the dma-mapping stuff inside DMA-buf. That clearly doesn't belong here. >>>>> >>>>> And this is why so many in the kernel community want to get rid of SG >>>>> lists. It would be great if DMA-BUF could also eliminate the need to >>>>> convert to an SGL, like Jason proposed. >>>>> >>>>> The DMA layer no longer needs SGL. These bugs belong to the DMA-BUF layer, >>>>> which is the one that depends on it. >>>> >>>> I'm all fine using an array/xarray of dma_addr_t in DMA-buf, just phys_vec is a clear no-go. >>> >>> You are proposing the same thing as an SGL, just in a different format. >> >> Yes, because that is the right thing todo as far as I can see. >> >>> It does not address the issue that dma_addr_t is expected to hold a DMA >>> address, while that is not always the case. For example, in the P2P case, >>> the addresses are not DMA addresses. >> >> Yes they are. They must be DMA addresses because that is the only thing the importer needs to do it's DMA. > > They can perform DMA, but that still does not make them suitable for the > dma_addr_t type. For the PCI_P2PDMA_MAP_BUS_ADDR flow, these addresses > follow completely different rules: they are not unmapped, require no cache > synchronization, are valid only for peer access, and require separate error > handling. The PCI_P2PDMA_MAP_BUS_ADDR is not supported by DMA-buf and as far as I can see is a complete dead end. > All of this information is lost if only the dma_addr_t is stored. Yes and that is fully intentional. DMA-buf handles that cleanly on the buffer object level and not like PCI_P2PDMA_MAP_BUS_ADDR as a completely broken design on a per address/page basis. Technical background is that the PCI_P2PDMA_MAP_BUS_ADDR approach can only be handled by a very very small subset of HW. Regards, Christian. > >> >> It can be that those are DMA addresses on private interconnects between devices, but it should *never* be a phys_addr_t because that is limited to the address space the CPU can see. >> >>> Jason's proposal: >>> https://lore.kernel.org/all/0-v1-b5cab63049c0+191af-dmabuf_map_type_jgg@nvidia.com/ >> >> Yeah, I have commented quite a bit on that. > > Right, I posted it for reference. > > Thanks > >> >> Regards, >> Christian. >> >>> >>> Thanks >>> >>>> >>>> Regards, >>>> Christian. >>>> >>>>> >>>>> Thanks >>>> >>>> >> >>