[PATCH 4/9] mm/memory: Batch set uffd-wp markers during zapping

[Dev Jain]

In preparation for the next patch, enable batch setting of uffd-wp ptes.

The code paths passing nr > 1 to zap_install_uffd_wp_if_needed() produce
that nr through either folio_pte_batch or swap_pte_batch, guaranteeing that
all ptes are the same w.r.t belonging to the same type of VMA (anonymous
or non-anonymous, wp-armed or non-wp-armed), and all being marked with
uffd-wp or all being not marked.

Note that we will have to use set_pte_at() in a loop instead of set_ptes()
since the latter cannot handle present->non-present conversion for
nr_pages > 1.

Convert documentation of install_uffd_wp_ptes_if_needed to kerneldoc
format.

No functional change is intended.

Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 include/linux/mm_inline.h | 37 +++++++++++++++++++++++--------------
 mm/memory.c               | 20 +-------------------
 mm/rmap.c                 |  2 +-
 3 files changed, 25 insertions(+), 34 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index ad50688d89dba..d69b9abbdf2a7 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -560,21 +560,30 @@ static inline pte_marker copy_pte_marker(
 	return dstm;
 }
 
-/*
- * If this pte is wr-protected by uffd-wp in any form, arm the special pte to
- * replace a none pte.  NOTE!  This should only be called when *pte is already
+/**
+ * install_uffd_wp_ptes_if_needed - install uffd-wp marker on PTEs that map
+ *				    consecutive pages of the same large folio.
+ * @vma: The VMA the pages are mapped into.
+ * @addr: Address the first page of this batch is mapped at.
+ * @ptep: Page table pointer for the first entry of this batch.
+ * @pteval: old value of the entry pointed to by ptep.
+ * @nr: Number of entries to clear (batch size).
+ *
+ * If the ptes were wr-protected by uffd-wp in any form, arm special ptes to
+ * replace none ptes.  NOTE!  This should only be called when *pte is already
  * cleared so we will never accidentally replace something valuable.  Meanwhile
  * none pte also means we are not demoting the pte so tlb flushed is not needed.
  * E.g., when pte cleared the caller should have taken care of the tlb flush.
  *
- * Must be called with pgtable lock held so that no thread will see the none
- * pte, and if they see it, they'll fault and serialize at the pgtable lock.
+ * Context: The caller holds the page table lock.  The PTEs map consecutive
+ * pages that belong to the same folio.  The PTEs are all in the same PMD
+ * and the same VMA.
  *
- * Returns true if an uffd-wp pte was installed, false otherwise.
+ * Returns true if uffd-wp ptes were installed, false otherwise.
  */
 static inline bool
-pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
-			      pte_t *pte, pte_t pteval)
+install_uffd_wp_ptes_if_needed(struct vm_area_struct *vma, unsigned long addr,
+			      pte_t *pte, pte_t pteval, unsigned int nr)
 {
 	bool arm_uffd_pte = false;
 
@@ -604,13 +613,13 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
 	if (unlikely(pte_swp_uffd_wp_any(pteval)))
 		arm_uffd_pte = true;
 
-	if (unlikely(arm_uffd_pte)) {
-		set_pte_at(vma->vm_mm, addr, pte,
-			   make_pte_marker(PTE_MARKER_UFFD_WP));
-		return true;
-	}
+	if (likely(!arm_uffd_pte))
+		return false;
 
-	return false;
+	for (int i = 0; i < nr; ++i, ++pte, addr += PAGE_SIZE)
+		set_pte_at(vma->vm_mm, addr, pte, make_pte_marker(PTE_MARKER_UFFD_WP));
+
+	return true;
 }
 
 static inline bool vma_has_recency(const struct vm_area_struct *vma)
diff --git a/mm/memory.c b/mm/memory.c
index 38062f8e11656..768646c0b3b6a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1594,29 +1594,11 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
 			      unsigned long addr, pte_t *pte, int nr,
 			      struct zap_details *details, pte_t pteval)
 {
-	bool was_installed = false;
-
-	if (!uffd_supports_wp_marker())
-		return false;
-
-	/* Zap on anonymous always means dropping everything */
-	if (vma_is_anonymous(vma))
-		return false;
-
 	if (zap_drop_markers(details))
 		return false;
 
-	for (;;) {
-		/* the PFN in the PTE is irrelevant. */
-		if (pte_install_uffd_wp_if_needed(vma, addr, pte, pteval))
-			was_installed = true;
-		if (--nr == 0)
-			break;
-		pte++;
-		addr += PAGE_SIZE;
-	}
+	return install_uffd_wp_ptes_if_needed(vma, addr, pte, pteval, nr);
 
-	return was_installed;
 }
 
 static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
diff --git a/mm/rmap.c b/mm/rmap.c
index a61978141ee3f..a7570cd037344 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2235,7 +2235,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		 * we may want to replace a none pte with a marker pte if
 		 * it's file-backed, so we don't lose the tracking info.
 		 */
-		pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval);
+		install_uffd_wp_ptes_if_needed(vma, address, pvmw.pte, pteval, 1);
 
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
-- 
2.34.1