linux-kernel - [PATCH v2 4/7] mm/mprotect: factor out check whether manual PTE write upgrades are required

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Message-Id: <20221108174652.198904-5-david@redhat.com>
Date:   Tue,  8 Nov 2022 18:46:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        David Hildenbrand <david@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Dave Chinner <david@...morbit.com>,
        Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v2 4/7] mm/mprotect: factor out check whether manual PTE write upgrades are required

Let's factor the check out into vma_wants_manual_pte_write_upgrade(), to be
reused in NUMA hinting fault context soon.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/mm.h | 16 ++++++++++++++--
 mm/mprotect.c      | 17 ++++-------------
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 517c8cc8ccb9..4a7c10bed8bd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1975,6 +1975,20 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma,
 #define  MM_CP_UFFD_WP_ALL                 (MM_CP_UFFD_WP | \
 					    MM_CP_UFFD_WP_RESOLVE)
 
+int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot);
+static inline bool vma_wants_manual_pte_write_upgrade(struct vm_area_struct *vma)
+{
+	/*
+	 * We want to check manually if we can change individual PTEs writable
+	 * if we can't do that automatically for all PTEs in a mapping. For
+	 * private mappings, that's always the case when we have write
+	 * permissions as we properly have to handle COW.
+	 */
+	if (vma->vm_flags & VM_SHARED)
+		return vma_wants_writenotify(vma, vma->vm_page_prot);
+	return !!(vma->vm_flags & VM_WRITE);
+
+}
 extern unsigned long change_protection(struct mmu_gather *tlb,
 			      struct vm_area_struct *vma, unsigned long start,
 			      unsigned long end, pgprot_t newprot,
@@ -2114,8 +2128,6 @@ static inline int pte_devmap(pte_t pte)
 }
 #endif
 
-int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot);
-
 extern pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
 			       spinlock_t **ptl);
 static inline pte_t *get_locked_pte(struct mm_struct *mm, unsigned long addr,
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 72aabffb7871..fe22db2c9cdd 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -558,8 +558,8 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long oldflags = vma->vm_flags;
 	long nrpages = (end - start) >> PAGE_SHIFT;
+	unsigned int mm_cp_flags = 0;
 	unsigned long charged = 0;
-	bool try_change_writable;
 	pgoff_t pgoff;
 	int error;
 
@@ -637,20 +637,11 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	 * held in write mode.
 	 */
 	vma->vm_flags = newflags;
-	/*
-	 * We want to check manually if we can change individual PTEs writable
-	 * if we can't do that automatically for all PTEs in a mapping. For
-	 * private mappings, that's always the case when we have write
-	 * permissions as we properly have to handle COW.
-	 */
-	if (vma->vm_flags & VM_SHARED)
-		try_change_writable = vma_wants_writenotify(vma, vma->vm_page_prot);
-	else
-		try_change_writable = !!(vma->vm_flags & VM_WRITE);
+	if (vma_wants_manual_pte_write_upgrade(vma))
+		mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
 	vma_set_page_prot(vma);
 
-	change_protection(tlb, vma, start, end, vma->vm_page_prot,
-			  try_change_writable ? MM_CP_TRY_CHANGE_WRITABLE : 0);
+	change_protection(tlb, vma, start, end, vma->vm_page_prot, mm_cp_flags);
 
 	/*
 	 * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
-- 
2.38.1