Re: [PATCH v3 11/15] mm/memory: factor out copying the actual PTE in copy_present_pte()

Mike Rapoport
2024-02-08T06:29:46Z

On Mon, Jan 29, 2024 at 01:46:45PM +0100, David Hildenbrand wrote:
> Let's prepare for further changes.
>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

> ---
> mm/memory.c | 63 ++++++++++++++++++++++++++++-------------------------
> 1 file changed, 33 insertions(+), 30 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 8d14ba440929..a3bdb25f4c8d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -930,6 +930,29 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
> return 0;
> }
>
> +static inline void __copy_present_pte(struct vm_area_struct *dst_vma,
> + struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte,
> + pte_t pte, unsigned long addr)
> +{
> + struct mm_struct *src_mm = src_vma->vm_mm;
> +
> + /* If it's a COW mapping, write protect it both processes. */
> + if (is_cow_mapping(src_vma->vm_flags) && pte_write(pte)) {
> + ptep_set_wrprotect(src_mm, addr, src_pte);
> + pte = pte_wrprotect(pte);
> + }
> +
> + /* If it's a shared mapping, mark it clean in the child. */
> + if (src_vma->vm_flags & VM_SHARED)
> + pte = pte_mkclean(pte);
> + pte = pte_mkold(pte);
> +
> + if (!userfaultfd_wp(dst_vma))
> + pte = pte_clear_uffd_wp(pte);
> +
> + set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
> +}
> +
> /*
> * Copy one pte. Returns 0 if succeeded, or -EAGAIN if one preallocated page
> * is required to copy this pte.
> @@ -939,23 +962,23 @@ copy_present_pte(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 folio **prealloc)
> {
> - struct mm_struct *src_mm = src_vma->vm_mm;
> - unsigned long vm_flags = src_vma->vm_flags;
> pte_t pte = ptep_get(src_pte);
> struct page *page;
> struct folio *folio;
>
> page = vm_normal_page(src_vma, addr, pte);
> - if (page)
> - folio = page_folio(page);
> - if (page && folio_test_anon(folio)) {
> + if (unlikely(!page))
> + goto copy_pte;
> +
> + folio = page_folio(page);
> + folio_get(folio);
> + if (folio_test_anon(folio)) {
> /*
> * 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.
> */
> - folio_get(folio);
> if (unlikely(folio_try_dup_anon_rmap_pte(folio, page, src_vma))) {
> /* Page may be pinned, we have to copy. */
> folio_put(folio);
> @@ -963,34 +986,14 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
> addr, rss, prealloc, page);
> }
> rss[MM_ANONPAGES]++;
> - } else if (page) {
> - folio_get(folio);
> + VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
> + } else {
> folio_dup_file_rmap_pte(folio, page);
> rss[mm_counter_file(folio)]++;
> }
>
> - /*
> - * If it's a COW mapping, write protect it both
> - * in the parent and the child
> - */
> - if (is_cow_mapping(vm_flags) && pte_write(pte)) {
> - ptep_set_wrprotect(src_mm, addr, src_pte);
> - pte = pte_wrprotect(pte);
> - }
> - VM_BUG_ON(page && folio_test_anon(folio) && PageAnonExclusive(page));
> -
> - /*
> - * If it's a shared mapping, mark it clean in
> - * the child
> - */
> - if (vm_flags & VM_SHARED)
> - pte = pte_mkclean(pte);
> - pte = pte_mkold(pte);
> -
> - if (!userfaultfd_wp(dst_vma))
> - pte = pte_clear_uffd_wp(pte);
> -
> - set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
> +copy_pte:
> + __copy_present_pte(dst_vma, src_vma, dst_pte, src_pte, pte, addr);
> return 0;
> }
>
> --
> 2.43.0
>
>

--
Sincerely yours,
Mike.