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From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org,
	David Hildenbrand <david@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
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Subject: [PATCH v1 07/11] mm/memory: factor out copying the actual PTE in copy_present_pte()
Date: Mon, 22 Jan 2024 20:41:56 +0100
Message-ID: <20240122194200.381241-8-david@redhat.com>
In-Reply-To: <20240122194200.381241-1-david@redhat.com>
References: <20240122194200.381241-1-david@redhat.com>
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Let's prepare for further changes.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory.c | 60 ++++++++++++++++++++++++++++-------------------------
 1 file changed, 32 insertions(+), 28 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7e1f4849463aa..2aa2051ee51d3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -930,6 +930,29 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 	return 0;
 }
 
+static inline void __copy_present_pte(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)
+{
+	struct mm_struct *src_mm = src_vma->vm_mm;
+
+	/* If it's a COW mapping, write protect it both processes. */
+	if (is_cow_mapping(src_vma->vm_flags) && pte_write(pte)) {
+		ptep_set_wrprotect(src_mm, addr, src_pte);
+		pte = pte_wrprotect(pte);
+	}
+
+	/* If it's a shared mapping, mark it clean in the child. */
+	if (src_vma->vm_flags & VM_SHARED)
+		pte = pte_mkclean(pte);
+	pte = pte_mkold(pte);
+
+	if (!userfaultfd_wp(dst_vma))
+		pte = pte_clear_uffd_wp(pte);
+
+	set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
+}
+
 /*
  * Copy one pte.  Returns 0 if succeeded, or -EAGAIN if one preallocated page
  * is required to copy this pte.
@@ -939,16 +962,16 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 		 pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
 		 struct folio **prealloc)
 {
-	struct mm_struct *src_mm = src_vma->vm_mm;
-	unsigned long vm_flags = src_vma->vm_flags;
 	pte_t pte = ptep_get(src_pte);
 	struct page *page;
 	struct folio *folio;
 
 	page = vm_normal_page(src_vma, addr, pte);
-	if (page)
-		folio = page_folio(page);
-	if (page && folio_test_anon(folio)) {
+	if (unlikely(!page))
+		goto copy_pte;
+
+	folio = page_folio(page);
+	if (folio_test_anon(folio)) {
 		/*
 		 * If this page may have been pinned by the parent process,
 		 * copy the page immediately for the child so that we'll always
@@ -963,34 +986,15 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 						 addr, rss, prealloc, page);
 		}
 		rss[MM_ANONPAGES]++;
-	} else if (page) {
+		VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
+	} else {
 		folio_get(folio);
 		folio_dup_file_rmap_pte(folio, page);
 		rss[mm_counter_file(page)]++;
 	}
 
-	/*
-	 * If it's a COW mapping, write protect it both
-	 * in the parent and the child
-	 */
-	if (is_cow_mapping(vm_flags) && pte_write(pte)) {
-		ptep_set_wrprotect(src_mm, addr, src_pte);
-		pte = pte_wrprotect(pte);
-	}
-	VM_BUG_ON(page && folio_test_anon(folio) && PageAnonExclusive(page));
-
-	/*
-	 * If it's a shared mapping, mark it clean in
-	 * the child
-	 */
-	if (vm_flags & VM_SHARED)
-		pte = pte_mkclean(pte);
-	pte = pte_mkold(pte);
-
-	if (!userfaultfd_wp(dst_vma))
-		pte = pte_clear_uffd_wp(pte);
-
-	set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
+copy_pte:
+	__copy_present_pte(dst_vma, src_vma, dst_pte, src_pte, pte, addr);
 	return 0;
 }
 
-- 
2.43.0