On Mon, 2017-07-17 at 09:06 -0700, Vineet Gupta wrote: > Hi Christoph, > > On 07/16/2017 11:42 PM, Christoph Hellwig wrote: > > > > I would expect that it would support any contiguous range in > > the kernel mapping (e.g. no vmalloc and friends).??But it's not > > documented anywhere, and if no in kernel users makes use of that > > fact at the moment it might be better to document a page size > > limitation and add asserts to enforce it. > > My first thought was indeed to add a BUG_ON for @size > PAGE_SIZE > (also accounting for offset etc), but I have a feeling this will > cause too many breakages. So perhaps it would be better to add the > fact to Documentation that it can handle any physically contiguous > range. Actually, that's not historically right. ?dma_map_single() was originally designed to be called on any region that was kmalloc'd meaning it was capable of mapping physically contiguous > PAGE_SIZE regions. For years (decades?) we've been eliminating the specialised dma_map_single() calls in favour of dma_map_sg, so it's possible there may not be any large region consumers anymore, so it *may* be safe to enforce a PAGE_SIZE limit, but not without auditing the remaining callers. James
