On Wed, Nov 04, 2020 at 04:54:19PM +0100, Daniel Vetter wrote: > I don't really have a box here, but dma_mmap_attrs() and friends to > mmap dma_alloc_coherent memory is set up as VM_IO | VM_PFNMAP (it's > actually enforced since underneath it uses remap_pfn_range), and > usually (except if it's pre-cma carveout) that's just normal struct > page backed memory. Sometimes from a cma region (so will be caught by > the cma page check), but if you have an iommu to make it > device-contiguous, that's not needed.
dma_mmap_* memory may or may not be page backed, but it absolutely must not be resolved by get_user_pages and friends as it is special. So yes, not being able to get a struct page back from such an mmap is a feature.
