linux-kernel - [PATCH v5 5/7] mm: Split can_change_pte_writable() into private and shared parts

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Message-Id: <20250718090244.21092-6-dev.jain@arm.com>
Date: Fri, 18 Jul 2025 14:32:42 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: ryan.roberts@....com,
	david@...hat.com,
	willy@...radead.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	catalin.marinas@....com,
	will@...nel.org,
	Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com,
	vbabka@...e.cz,
	jannh@...gle.com,
	anshuman.khandual@....com,
	peterx@...hat.com,
	joey.gouly@....com,
	ioworker0@...il.com,
	baohua@...nel.org,
	kevin.brodsky@....com,
	quic_zhenhuah@...cinc.com,
	christophe.leroy@...roup.eu,
	yangyicong@...ilicon.com,
	linux-arm-kernel@...ts.infradead.org,
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	ziy@...dia.com,
	Dev Jain <dev.jain@....com>
Subject: [PATCH v5 5/7] mm: Split can_change_pte_writable() into private and shared parts

In preparation for patch 6 and modularizing the code in general, split
can_change_pte_writable() into private and shared VMA parts. No functional
change intended.

Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Dev Jain <dev.jain@....com>
---
 mm/mprotect.c | 50 ++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 4977f198168e..a1c7d8a4648d 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -40,11 +40,8 @@
 
 #include "internal.h"
 
-bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
-			     pte_t pte)
+static bool maybe_change_pte_writable(struct vm_area_struct *vma, pte_t pte)
 {
-	struct page *page;
-
 	if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)))
 		return false;
 
@@ -60,16 +57,32 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
 	if (userfaultfd_pte_wp(vma, pte))
 		return false;
 
-	if (!(vma->vm_flags & VM_SHARED)) {
-		/*
-		 * Writable MAP_PRIVATE mapping: We can only special-case on
-		 * exclusive anonymous pages, because we know that our
-		 * write-fault handler similarly would map them writable without
-		 * any additional checks while holding the PT lock.
-		 */
-		page = vm_normal_page(vma, addr, pte);
-		return page && PageAnon(page) && PageAnonExclusive(page);
-	}
+	return true;
+}
+
+static bool can_change_private_pte_writable(struct vm_area_struct *vma,
+					    unsigned long addr, pte_t pte)
+{
+	struct page *page;
+
+	if (!maybe_change_pte_writable(vma, pte))
+		return false;
+
+	/*
+	 * Writable MAP_PRIVATE mapping: We can only special-case on
+	 * exclusive anonymous pages, because we know that our
+	 * write-fault handler similarly would map them writable without
+	 * any additional checks while holding the PT lock.
+	 */
+	page = vm_normal_page(vma, addr, pte);
+	return page && PageAnon(page) && PageAnonExclusive(page);
+}
+
+static bool can_change_shared_pte_writable(struct vm_area_struct *vma,
+					   pte_t pte)
+{
+	if (!maybe_change_pte_writable(vma, pte))
+		return false;
 
 	VM_WARN_ON_ONCE(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte));
 
@@ -83,6 +96,15 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
 	return pte_dirty(pte);
 }
 
+bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
+			     pte_t pte)
+{
+	if (!(vma->vm_flags & VM_SHARED))
+		return can_change_private_pte_writable(vma, addr, pte);
+
+	return can_change_shared_pte_writable(vma, pte);
+}
+
 static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep,
 				    pte_t pte, int max_nr_ptes)
 {
-- 
2.30.2