From: David Hildenbrand Subject: mm/memory: slightly simplify copy_present_pte() Let's move the pinning check into the caller, to simplify return code logic and prepare for further changes: relocating the page_needs_cow_for_dma() into rmap handling code. While at it, remove the unused pte parameter and simplify the comments a bit. No functional change intended. Link: https://lkml.kernel.org/r/20220329160440.193848-4-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: David Rientjes Cc: Don Dutile Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Jason Gunthorpe Cc: John Hubbard Cc: Khalid Aziz Cc: "Kirill A. Shutemov" Cc: Liang Zhang Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Kravetz Cc: Mike Rapoport Cc: Nadav Amit Cc: Oded Gabbay Cc: Oleg Nesterov Cc: Pedro Demarchi Gomes Cc: Peter Xu Cc: Rik van Riel Cc: Roman Gushchin Cc: Shakeel Butt Cc: Yang Shi Signed-off-by: Andrew Morton --- mm/memory.c | 53 +++++++++++++++----------------------------------- 1 file changed, 16 insertions(+), 37 deletions(-) --- a/mm/memory.c~mm-memory-slightly-simplify-copy_present_pte +++ a/mm/memory.c @@ -862,19 +862,11 @@ copy_nonpresent_pte(struct mm_struct *ds } /* - * Copy a present and normal page if necessary. + * Copy a present and normal page. * - * NOTE! The usual case is that this doesn't need to do - * anything, and can just return a positive value. That - * will let the caller know that it can just increase - * the page refcount and re-use the pte the traditional - * way. - * - * But _if_ we need to copy it because it needs to be - * pinned in the parent (and the child should get its own - * copy rather than just a reference to the same page), - * we'll do that here and return zero to let the caller - * know we're done. + * NOTE! The usual case is that this isn't required; + * instead, the caller can just increase the page refcount + * and re-use the pte the traditional way. * * And if we need a pre-allocated page but don't yet have * one, return a negative error to let the preallocation @@ -884,25 +876,10 @@ copy_nonpresent_pte(struct mm_struct *ds static inline int copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss, - struct page **prealloc, pte_t pte, struct page *page) + struct page **prealloc, struct page *page) { struct page *new_page; - - /* - * What we want to do is to check whether this page may - * have been pinned by the parent process. If so, - * instead of wrprotect the pte on both sides, we copy - * the page immediately so that we'll always guarantee - * the pinned page won't be randomly replaced in the - * future. - * - * The page pinning checks are just "has this mm ever - * seen pinning", along with the (inexact) check of - * the page count. That might give false positives for - * for pinning, but it will work correctly. - */ - if (likely(!page_needs_cow_for_dma(src_vma, page))) - return 1; + pte_t pte; new_page = *prealloc; if (!new_page) @@ -944,14 +921,16 @@ copy_present_pte(struct vm_area_struct * struct page *page; page = vm_normal_page(src_vma, addr, pte); - if (page) { - int retval; - - retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte, - addr, rss, prealloc, pte, page); - if (retval <= 0) - return retval; - + if (page && unlikely(page_needs_cow_for_dma(src_vma, page))) { + /* + * If this page may have been pinned by the parent process, + * copy the page immediately for the child so that we'll always + * guarantee the pinned page won't be randomly replaced in the + * future. + */ + return copy_present_page(dst_vma, src_vma, dst_pte, src_pte, + addr, rss, prealloc, page); + } else if (page) { get_page(page); page_dup_rmap(page, false); rss[mm_counter(page)]++; _