[PATCH v2 4/4] mm: remove boolean output parameters from folio_pte_batch_ext()

[David Hildenbrand]

Instead, let's just allow for specifying through flags whether we want
to have bits merged into the original PTE.

For the madvise() case, simplify by having only a single parameter for
merging young+dirty. For madvise_cold_or_pageout_pte_range() merging the
dirty bit is not required, but also not harmful. This code is not that
performance critical after all to really force all micro-optimizations.

As we now have two pte_t * parameters, use PageTable() to make sure we
are actually given a pointer at a copy of the PTE, not a pointer into
an actual page table.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/internal.h | 65 +++++++++++++++++++++++++++++++++------------------
 mm/madvise.c  | 26 ++++-----------------
 mm/memory.c   |  8 ++-----
 mm/util.c     |  2 +-
 4 files changed, 50 insertions(+), 51 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 6c92956ac4fd9..b7131bd3d1ad1 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -208,6 +208,18 @@ typedef int __bitwise fpb_t;
 /* Compare PTEs respecting the soft-dirty bit. */
 #define FPB_RESPECT_SOFT_DIRTY		((__force fpb_t)BIT(1))
 
+/*
+ * Merge PTE write bits: if any PTE in the batch is writable, modify the
+ * PTE at @ptentp to be writable.
+ */
+#define FPB_MERGE_WRITE			((__force fpb_t)BIT(2))
+
+/*
+ * Merge PTE young and dirty bits: if any PTE in the batch is young or dirty,
+ * modify the PTE at @ptentp to be young or dirty, respectively.
+ */
+#define FPB_MERGE_YOUNG_DIRTY		((__force fpb_t)BIT(3))
+
 static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
 {
 	if (!(flags & FPB_RESPECT_DIRTY))
@@ -220,16 +232,12 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
 /**
  * folio_pte_batch_flags - detect a PTE batch for a large folio
  * @folio: The large folio to detect a PTE batch for.
+ * @vma: The VMA. Only relevant with FPB_MERGE_WRITE, otherwise can be NULL.
  * @ptep: Page table pointer for the first entry.
- * @pte: Page table entry for the first page.
+ * @ptentp: Pointer to a COPY of the first page table entry whose flags this
+ *	    function updates based on @flags if appropriate.
  * @max_nr: The maximum number of table entries to consider.
  * @flags: Flags to modify the PTE batch semantics.
- * @any_writable: Optional pointer to indicate whether any entry except the
- *		  first one is writable.
- * @any_young: Optional pointer to indicate whether any entry except the
- *		  first one is young.
- * @any_dirty: Optional pointer to indicate whether any entry except the
- *		  first one is dirty.
  *
  * Detect a PTE batch: consecutive (present) PTEs that map consecutive
  * pages of the same large folio in a single VMA and a single page table.
@@ -242,28 +250,32 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
  * must be limited by the caller so scanning cannot exceed a single VMA and
  * a single page table.
  *
+ * Depending on the FPB_MERGE_* flags, the pte stored at @ptentp will
+ * be updated: it's crucial that a pointer to a COPY of the first
+ * page table entry, obtained through ptep_get(), is provided as @ptentp.
+ *
  * This function will be inlined to optimize based on the input parameters;
  * consider using folio_pte_batch() instead if applicable.
  *
  * Return: the number of table entries in the batch.
  */
 static inline unsigned int folio_pte_batch_flags(struct folio *folio,
-		pte_t *ptep, pte_t pte, unsigned int max_nr, fpb_t flags,
-		bool *any_writable, bool *any_young, bool *any_dirty)
+		struct vm_area_struct *vma, pte_t *ptep, pte_t *ptentp,
+		unsigned int max_nr, fpb_t flags)
 {
+	bool any_writable = false, any_young = false, any_dirty = false;
+	pte_t expected_pte, pte = *ptentp;
 	unsigned int nr, cur_nr;
-	pte_t expected_pte;
-
-	if (any_writable)
-		*any_writable = false;
-	if (any_young)
-		*any_young = false;
-	if (any_dirty)
-		*any_dirty = false;
 
 	VM_WARN_ON_FOLIO(!pte_present(pte), folio);
 	VM_WARN_ON_FOLIO(!folio_test_large(folio) || max_nr < 1, folio);
 	VM_WARN_ON_FOLIO(page_folio(pfn_to_page(pte_pfn(pte))) != folio, folio);
+	/*
+	 * Ensure this is a pointer to a copy not a pointer into a page table.
+	 * If this is a stack value, it won't be a valid virtual address, but
+	 * that's fine because it also cannot be pointing into the page table.
+	 */
+	VM_WARN_ON(virt_addr_valid(ptentp) && PageTable(virt_to_page(ptentp)));
 
 	/* Limit max_nr to the actual remaining PFNs in the folio we could batch. */
 	max_nr = min_t(unsigned long, max_nr,
@@ -279,12 +291,12 @@ static inline unsigned int folio_pte_batch_flags(struct folio *folio,
 		if (!pte_same(__pte_batch_clear_ignored(pte, flags), expected_pte))
 			break;
 
-		if (any_writable)
-			*any_writable |= pte_write(pte);
-		if (any_young)
-			*any_young |= pte_young(pte);
-		if (any_dirty)
-			*any_dirty |= pte_dirty(pte);
+		if (flags & FPB_MERGE_WRITE)
+			any_writable |= pte_write(pte);
+		if (flags & FPB_MERGE_YOUNG_DIRTY) {
+			any_young |= pte_young(pte);
+			any_dirty |= pte_dirty(pte);
+		}
 
 		cur_nr = pte_batch_hint(ptep, pte);
 		expected_pte = pte_advance_pfn(expected_pte, cur_nr);
@@ -292,6 +304,13 @@ static inline unsigned int folio_pte_batch_flags(struct folio *folio,
 		nr += cur_nr;
 	}
 
+	if (any_writable)
+		*ptentp = pte_mkwrite(*ptentp, vma);
+	if (any_young)
+		*ptentp = pte_mkyoung(*ptentp);
+	if (any_dirty)
+		*ptentp = pte_mkdirty(*ptentp);
+
 	return min(nr, max_nr);
 }
 
diff --git a/mm/madvise.c b/mm/madvise.c
index fe363a14daab3..9de9b7c797c63 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -344,13 +344,12 @@ static inline bool can_do_file_pageout(struct vm_area_struct *vma)
 
 static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end,
 					  struct folio *folio, pte_t *ptep,
-					  pte_t pte, bool *any_young,
-					  bool *any_dirty)
+					  pte_t *ptentp)
 {
 	int max_nr = (end - addr) / PAGE_SIZE;
 
-	return folio_pte_batch_flags(folio, ptep, pte, max_nr, 0, NULL,
-				     any_young, any_dirty);
+	return folio_pte_batch_flags(folio, NULL, ptep, ptentp, max_nr,
+				     FPB_MERGE_YOUNG_DIRTY);
 }
 
 static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
@@ -488,13 +487,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		 * next pte in the range.
 		 */
 		if (folio_test_large(folio)) {
-			bool any_young;
-
-			nr = madvise_folio_pte_batch(addr, end, folio, pte,
-						     ptent, &any_young, NULL);
-			if (any_young)
-				ptent = pte_mkyoung(ptent);
-
+			nr = madvise_folio_pte_batch(addr, end, folio, pte, &ptent);
 			if (nr < folio_nr_pages(folio)) {
 				int err;
 
@@ -724,11 +717,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 		 * next pte in the range.
 		 */
 		if (folio_test_large(folio)) {
-			bool any_young, any_dirty;
-
-			nr = madvise_folio_pte_batch(addr, end, folio, pte,
-						     ptent, &any_young, &any_dirty);
-
+			nr = madvise_folio_pte_batch(addr, end, folio, pte, &ptent);
 			if (nr < folio_nr_pages(folio)) {
 				int err;
 
@@ -753,11 +742,6 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 					nr = 0;
 				continue;
 			}
-
-			if (any_young)
-				ptent = pte_mkyoung(ptent);
-			if (any_dirty)
-				ptent = pte_mkdirty(ptent);
 		}
 
 		if (folio_test_swapcache(folio) || folio_test_dirty(folio)) {
diff --git a/mm/memory.c b/mm/memory.c
index 26a82b82863b0..0269edb520987 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -972,10 +972,9 @@ copy_present_ptes(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,
 		 int max_nr, int *rss, struct folio **prealloc)
 {
+	fpb_t flags = FPB_MERGE_WRITE;
 	struct page *page;
 	struct folio *folio;
-	bool any_writable;
-	fpb_t flags = 0;
 	int err, nr;
 
 	page = vm_normal_page(src_vma, addr, pte);
@@ -995,8 +994,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 		if (vma_soft_dirty_enabled(src_vma))
 			flags |= FPB_RESPECT_SOFT_DIRTY;
 
-		nr = folio_pte_batch_flags(folio, src_pte, pte, max_nr, flags,
-					   &any_writable, NULL, NULL);
+		nr = folio_pte_batch_flags(folio, src_vma, src_pte, &pte, max_nr, flags);
 		folio_ref_add(folio, nr);
 		if (folio_test_anon(folio)) {
 			if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,
@@ -1010,8 +1008,6 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 			folio_dup_file_rmap_ptes(folio, page, nr, dst_vma);
 			rss[mm_counter_file(folio)] += nr;
 		}
-		if (any_writable)
-			pte = pte_mkwrite(pte, src_vma);
 		__copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte,
 				    addr, nr);
 		return nr;
diff --git a/mm/util.c b/mm/util.c
index cf41edceec7d2..ce826ca82a11d 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1197,6 +1197,6 @@ EXPORT_SYMBOL(compat_vma_mmap_prepare);
 unsigned int folio_pte_batch(struct folio *folio, pte_t *ptep, pte_t pte,
 		unsigned int max_nr)
 {
-	return folio_pte_batch_flags(folio, ptep, pte, max_nr, 0, NULL, NULL, NULL);
+	return folio_pte_batch_flags(folio, NULL, ptep, &pte, max_nr, 0);
 }
 #endif /* CONFIG_MMU */
-- 
2.49.0