From: Jarkko Sakkinen > Sent: 06 March 2022 05:32 > > For device memory (aka VM_IO | VM_PFNMAP) MAP_POPULATE does nothing. Allow > to use that for initializing the device memory by providing a new callback > f_ops->populate() for the purpose. > > SGX patches are provided to show the callback in context. > > An obvious alternative is a ioctl but it is less elegant and requires > two syscalls (mmap + ioctl) per memory range, instead of just one > (mmap). Is this all about trying to stop the vm_operations_struct.fault() function being called? It is pretty easy to ensure the mappings are setup in the driver's mmap() function. Then the fault() function can just return -VM_FAULT_SIGBUS; If it is actually device memory you just need to call vm_iomap_memory() That quite nicely mmap()s PCIe memory space into a user process. Mapping driver memory is slightly more difficult. For buffers allocated with dma_alloc_coherent() you can probably use dma_mmap_coherent(). But I have a loop calling remap_pfn_range() because the buffer area is made of multiple 16kB kernel buffers that need to be mapped to contiguous user pages. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
