[PATCH 08/15] mm: introduce and use linear_folio_page_index()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

This function is, for now, a placeholder; it will be used in future to
determine whether to use the virtual page index or not, based on whether
the folio is anonymous or not.

Currently it simply wraps linear_page_index(), so this does not change
behaviour.

We update callers that will, once the change is introduced to track
anonymous folios by virtual page offset if MAP_PRIVATE file-backed, need to
determine which index to use based on folio type.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/pagemap.h | 18 ++++++++++++++++++
 mm/huge_memory.c        |  3 ++-
 mm/migrate.c            |  6 ++++--
 mm/userfaultfd.c        |  6 ++++--
 4 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 81da91e103b3..dab355eda0ef 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1142,6 +1142,24 @@ static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
 	return pgoff;
 }
 
+/**
+ * linear_folio_page_index() - Determine the absolute page offset of
+ * @address within @vma from @folio.
+ * @folio: The folio whose linear page index is sought.
+ * @vma: The VMA in which @address resides.
+ * @address: The address whose absolute page offset is required.
+ *
+ * For compatibility, currently identical to linear_page_index().
+ *
+ * Returns: The absolute page offset of @address within @vma.
+ */
+static inline pgoff_t linear_folio_page_index(const struct folio *folio,
+					      const struct vm_area_struct *vma,
+					      const unsigned long address)
+{
+	return linear_page_index(vma, address);
+}
+
 struct wait_page_key {
 	struct folio *folio;
 	int bit_nr;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9b1f3b24f7e0..abc65d608c23 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2887,7 +2887,8 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
 		}
 
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 
 		_dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot);
 		/* Follow mremap() behavior and treat the entry dirty after the move */
diff --git a/mm/migrate.c b/mm/migrate.c
index 222c8c15f782..37fe7a9b3fac 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -363,8 +363,10 @@ static bool remove_migration_pte(struct folio *folio,
 		unsigned long idx = 0;
 
 		/* pgoff is invalid for ksm pages, but they are never large */
-		if (folio_test_large(folio) && !folio_test_hugetlb(folio))
-			idx = linear_page_index(vma, pvmw.address) - pvmw.pgoff;
+		if (folio_test_large(folio) && !folio_test_hugetlb(folio)) {
+			idx += linear_folio_page_index(folio, vma, pvmw.address);
+			idx -= pvmw.pgoff;
+		}
 		new = folio_page(folio, idx);
 
 #ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 8fd24c8b428e..258b03182a78 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1352,7 +1352,8 @@ static long move_present_ptes(struct mm_struct *mm,
 		}
 
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 
 		orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
 		/* Set soft dirty bit so userspace can notice the pte was moved */
@@ -1428,7 +1429,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
 	 */
 	if (src_folio) {
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 	} else {
 		/*
 		 * Check if the swap entry is cached after acquiring the src_pte

-- 
2.55.0