[PATCH 2/5] mm/gup: split follow_page_pte_commit() out of follow_page_pte()

[Rik van Riel <riel@surriel.com>]

follow_page_pte() does two things once it has resolved a present PTE
to a page: run the per-PTE safety checks (write-fault, unshare), then
commit to that page: grab a ref, fault it in if pinning, mark it
dirty/accessed, and hand it back to the caller.

Split the second part into its own follow_page_pte_commit(), unchanged
except for taking its inputs as parameters instead of local variables.
A later change teaches it to commit more than one page at a time.

No functional changes intended.

Suggested-by: David Hildenbrand <david@kernel.org>
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Rik van Riel <riel@surriel.com>
---
 mm/gup.c | 86 ++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 53 insertions(+), 33 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 09c64ef2f57c..053da43760a2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -813,6 +813,56 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page,
 	return !userfaultfd_pte_wp(vma, pte);
 }
 
+/*
+ * The caller has already run every per-PTE safety check (present,
+ * write-fault, gup_must_unshare()) on the PTE, so this only does the
+ * per-folio work: the refcount grab, the FOLL_PIN accessibility fault-in,
+ * dirty/accessed marking, and the array fill with the cache flush.
+ */
+static long follow_page_pte_commit(struct vm_area_struct *vma,
+		unsigned long address, struct folio *folio, struct page *page,
+		pte_t pte, unsigned int flags, struct page **pages)
+{
+	long ret;
+
+	/* try_grab_folio() does nothing unless FOLL_GET or FOLL_PIN is set. */
+	ret = try_grab_folio(folio, 1, flags);
+	if (unlikely(ret))
+		return ret;
+
+	/*
+	 * We need to make the page accessible if and only if we are going
+	 * to access its content (the FOLL_PIN case).  Please see
+	 * Documentation/core-api/pin_user_pages.rst for details.
+	 */
+	if (flags & FOLL_PIN) {
+		ret = arch_make_folio_accessible(folio);
+		if (ret) {
+			gup_put_folio(folio, 1, flags);
+			return ret;
+		}
+	}
+	if (flags & FOLL_TOUCH) {
+		if ((flags & FOLL_WRITE) &&
+		    !pte_dirty(pte) && !folio_test_dirty(folio))
+			folio_mark_dirty(folio);
+		/*
+		 * pte_mkyoung() would be more correct here, but atomic care
+		 * is needed to avoid losing the dirty bit: it is easier to use
+		 * folio_mark_accessed().
+		 */
+		folio_mark_accessed(folio);
+	}
+
+	if (pages) {
+		pages[0] = page;
+		flush_anon_page(vma, page, address);
+		flush_dcache_page(page);
+	}
+
+	return 0;
+}
+
 static long follow_page_pte(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd, unsigned int flags,
 		struct page **pages)
@@ -868,40 +918,10 @@ static long follow_page_pte(struct vm_area_struct *vma,
 	VM_WARN_ON_ONCE_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
 			     !PageAnonExclusive(page), page);
 
-	/* try_grab_folio() does nothing unless FOLL_GET or FOLL_PIN is set. */
-	ret = try_grab_folio(folio, 1, flags);
-	if (unlikely(ret))
+	ret = follow_page_pte_commit(vma, address, folio, page, pte, flags,
+				     pages);
+	if (ret)
 		goto out;
-
-	/*
-	 * We need to make the page accessible if and only if we are going
-	 * to access its content (the FOLL_PIN case).  Please see
-	 * Documentation/core-api/pin_user_pages.rst for details.
-	 */
-	if (flags & FOLL_PIN) {
-		ret = arch_make_folio_accessible(folio);
-		if (ret) {
-			gup_put_folio(folio, 1, flags);
-			goto out;
-		}
-	}
-	if (flags & FOLL_TOUCH) {
-		if ((flags & FOLL_WRITE) &&
-		    !pte_dirty(pte) && !folio_test_dirty(folio))
-			folio_mark_dirty(folio);
-		/*
-		 * pte_mkyoung() would be more correct here, but atomic care
-		 * is needed to avoid losing the dirty bit: it is easier to use
-		 * folio_mark_accessed().
-		 */
-		folio_mark_accessed(folio);
-	}
-
-	if (pages) {
-		pages[0] = page;
-		flush_anon_page(vma, page, address);
-		flush_dcache_page(page);
-	}
 	ret = 1;
 out:
 	pte_unmap_unlock(ptep, ptl);
-- 
2.53.0-Meta