From: John Hubbard <jhubbard@xxxxxxxxxx> Subject: mm/gup: follow_pfn_pte(): -EEXIST cleanup Remove a quirky special case from follow_pfn_pte(), and adjust its callers to match. Caller changes include: __get_user_pages(): Regardless of any FOLL_* flags, get_user_pages() and its variants should handle PFN-only entries by stopping early, if the caller expected **pages to be filled in. This makes for a more reliable API, as compared to the previous approach of skipping over such entries (and thus leaving them silently unwritten). move_pages(): squash the -EEXIST error return from follow_page() into -EFAULT, because -EFAULT is listed in the man page, whereas -EEXIST is not. Link: https://lkml.kernel.org/r/20220204020010.68930-3-jhubbard@xxxxxxxxxx Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/mm/gup.c~mm-gup-follow_pfn_pte-eexist-cleanup +++ a/mm/gup.c @@ -464,10 +464,6 @@ static struct page *no_page_table(struct static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address, pte_t *pte, unsigned int flags) { - /* No page to get reference */ - if (flags & (FOLL_GET | FOLL_PIN)) - return -EFAULT; - if (flags & FOLL_TOUCH) { pte_t entry = *pte; @@ -1205,8 +1201,15 @@ retry: } else if (PTR_ERR(page) == -EEXIST) { /* * Proper page table entry exists, but no corresponding - * struct page. + * struct page. If the caller expects **pages to be + * filled in, bail out now, because that can't be done + * for this page. */ + if (pages) { + ret = PTR_ERR(page); + goto out; + } + goto next_page; } else if (IS_ERR(page)) { ret = PTR_ERR(page); --- a/mm/migrate.c~mm-gup-follow_pfn_pte-eexist-cleanup +++ a/mm/migrate.c @@ -1762,6 +1762,13 @@ static int do_pages_move(struct mm_struc } /* + * The move_pages() man page does not have an -EEXIST choice, so + * use -EFAULT instead. + */ + if (err == -EEXIST) + err = -EFAULT; + + /* * If the page is already on the target node (!err), store the * node, otherwise, store the err. */ _
