On 11/16/2022 9:45 AM, Christoph Hellwig wrote: > On Wed, Nov 16, 2022 at 03:15:10PM +0000, Robin Murphy wrote: >> Coherent DMA buffers are allocated by a kernel driver or subsystem for the >> use of a device managed by that driver or subsystem, and thus they >> fundamentally belong to the kernel as proxy for the device. Any coherent >> DMA buffer may be mapped to userspace with the dma_mmap_*() interfaces, but >> they're never a "userspace allocation" in that sense. > > Exactly. I could not find a place to map the buffers to userspace, > so if it does that without using the proper interfaces we need to fix > that as well. Dean, can you point me to the mmap code? See hfi1_file_mmap(), cases RCV_HDRQ and RCV_EGRBUF, for the two items you changed in hfi1. Both directly use remap_pfn_range(), which is probably the original approved call, but now is now buried deep within dma_mmap_*(). As you say - these should be updated. That said, the eager buffer mapping will stitch together multiple eager buffers into a single user map/vma. I don't see how to do that with the dma_mmap_*() interface. -Dean External recipient
