mm: make GUP handle pfn mapping unless FOLL_GET is requested
With DAX, pfn mapping becoming more common. The patch adjusts GUP code to cover pfn mapping for cases when we don't need struct page to proceed. To make it possible, let's change follow_page() code to return -EEXIST error code if proper page table entry exists, but no corresponding struct page. __get_user_page() would ignore the error code and move to the next page frame. The immediate effect of the change is working MAP_POPULATE and mlock() on DAX mappings. [akpm@linux-foundation.org: fix arm64 build] Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: NToshi Kani <toshi.kani@hp.com> Acked-by: NMatthew Wilcox <willy@linux.intel.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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