On Wed, Jan 30, 2019 at 04:18:48AM +0000, Jason Gunthorpe wrote: > Every attempt to give BAR memory to struct page has run into major > trouble, IMHO, so I like that this approach avoids that. Way less problems than not having struct page for doing anything non-trivial. If you map the BAR to userspace with remap_pfn_range and friends the mapping is indeed very simple. But any operation that expects a page structure, which is at least everything using get_user_pages won't work. So you can't do direct I/O to your remapped BAR, you can't create MRs on it, etc, etc.
