[PATCH v4 04/12] 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, therefore
batching is correct:

1) all ptes belong to the same type of VMA (anonymous or non-anonymous,
   wp-armed or non-wp-armed)

2) all ptes being marked with uffd-wp or all being not marked (same is the
   case with the pte_swp_uffd_wp_any check)

3) uffd_supports_wp_marker() is independent of the function parameters

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.

Rename the function to cond_install_uffd_wp_ptes, and convert the
documentation to kerneldoc format.

Move the function to memory.c since this has grown too long to be kept
in mm_inline.h, while retaining the inline hint.

Rename pte->ptep and pteval->pte.

Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 include/linux/mm.h        |  4 ++
 include/linux/mm_inline.h | 53 -------------------------
 mm/memory.c               | 81 ++++++++++++++++++++++++++++++---------
 mm/rmap.c                 |  2 +-
 4 files changed, 67 insertions(+), 73 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 31e27ff6a35fa..3169bd6d69f5a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -5216,4 +5216,8 @@ void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte,
 		struct vm_area_struct *vma, unsigned long addr,
 		bool uffd_wp);
 
+bool cond_install_uffd_wp_ptes(struct vm_area_struct *vma, unsigned long addr,
+		pte_t *ptep, pte_t pte, unsigned long nr_ptes);
+
+
 #endif /* _LINUX_MM_H */
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index a171070e15f05..1a65c2bda2398 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -566,59 +566,6 @@ 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
- * 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.
- *
- * Returns true if an uffd-wp pte was 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)
-{
-	bool arm_uffd_pte = false;
-
-	if (!uffd_supports_wp_marker())
-		return false;
-
-	/* The current status of the pte should be "cleared" before calling */
-	WARN_ON_ONCE(!pte_none(ptep_get(pte)));
-
-	/*
-	 * NOTE: userfaultfd_wp_unpopulated() doesn't need this whole
-	 * thing, because when zapping either it means it's dropping the
-	 * page, or in TTU where the present pte will be quickly replaced
-	 * with a swap pte.  There's no way of leaking the bit.
-	 */
-	if (vma_is_anonymous(vma) || !userfaultfd_wp(vma))
-		return false;
-
-	/* A uffd-wp wr-protected normal pte */
-	if (unlikely(pte_present(pteval) && pte_uffd_wp(pteval)))
-		arm_uffd_pte = true;
-
-	/*
-	 * A uffd-wp wr-protected swap pte.  Note: this should even cover an
-	 * existing pte marker with uffd-wp bit set.
-	 */
-	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;
-	}
-
-	return false;
-}
-
 static inline bool vma_has_recency(const struct vm_area_struct *vma)
 {
 	if (vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))
diff --git a/mm/memory.c b/mm/memory.c
index 0c9d9c2cbf0e0..767c033e95da9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1599,6 +1599,67 @@ static inline bool zap_drop_markers(struct zap_details *details)
 	return details->zap_flags & ZAP_FLAG_DROP_MARKER;
 }
 
+/**
+ * cond_install_uffd_wp_ptes - install uffd-wp marker after clearing PTEs
+ *			       that mapped 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.
+ * @pte: old value of the entry pointed to by ptep.
+ * @nr_ptes: 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.
+ *
+ * Returns true if uffd-wp ptes were installed, false otherwise.
+ */
+inline bool cond_install_uffd_wp_ptes(struct vm_area_struct *vma, unsigned long addr,
+		pte_t *ptep, pte_t pte, unsigned long nr_ptes)
+{
+	bool arm_uffd_pte = false;
+
+	if (!uffd_supports_wp_marker())
+		return false;
+
+	/* The current status of the pte should be "cleared" before calling */
+	WARN_ON_ONCE(!pte_none(ptep_get(ptep)));
+
+	/*
+	 * NOTE: userfaultfd_wp_unpopulated() doesn't need this whole
+	 * thing, because when zapping either it means it's dropping the
+	 * page, or in TTU where the present pte will be quickly replaced
+	 * with a swap pte.  There's no way of leaking the bit.
+	 */
+	if (vma_is_anonymous(vma) || !userfaultfd_wp(vma))
+		return false;
+
+	/* A uffd-wp wr-protected normal pte */
+	if (unlikely(pte_present(pte) && pte_uffd_wp(pte)))
+		arm_uffd_pte = true;
+
+	/*
+	 * A uffd-wp wr-protected swap pte.  Note: this should even cover an
+	 * existing pte marker with uffd-wp bit set.
+	 */
+	if (unlikely(pte_swp_uffd_wp_any(pte)))
+		arm_uffd_pte = true;
+
+	if (likely(!arm_uffd_pte))
+		return false;
+
+	for (int i = 0; i < nr_ptes; ++i, ++ptep, addr += PAGE_SIZE)
+		set_pte_at(vma->vm_mm, addr, ptep, make_pte_marker(PTE_MARKER_UFFD_WP));
+
+	return true;
+}
+
 /*
  * This function makes sure that we'll replace the none pte with an uffd-wp
  * swap special pte marker when necessary. Must be with the pgtable lock held.
@@ -1610,29 +1671,11 @@ 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 cond_install_uffd_wp_ptes(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 12bbee57f20da..6a0b43856d6c0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2288,7 +2288,7 @@ 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);
+		cond_install_uffd_wp_ptes(vma, address, pvmw.pte, pteval, 1);
 
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
-- 
2.34.1