7 files changed, 144 insertions, 70 deletions
diff --git a/mm/madvise.c b/mm/madvise.c
index fb1c86e630b663..0b3280752bfb79 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -167,7 +167,7 @@ static int madvise_update_vma(vm_flags_t new_flags,
 			range->start, range->end, anon_name);
 	else
 		vma = vma_modify_flags(&vmi, madv_behavior->prev, vma,
-			range->start, range->end, new_flags);
+			range->start, range->end, &new_flags);
 
 	if (IS_ERR(vma))
 		return PTR_ERR(vma);
diff --git a/mm/mlock.c b/mm/mlock.c
index bb0776f5ef7cad..2f699c3497a579 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -478,7 +478,7 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
 		goto out;
 
-	vma = vma_modify_flags(vmi, *prev, vma, start, end, newflags);
+	vma = vma_modify_flags(vmi, *prev, vma, start, end, &newflags);
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
 		goto out;
diff --git a/mm/mprotect.c b/mm/mprotect.c
index ab4e06cd9a6977..db93d3bb1a5e70 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -756,7 +756,7 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
 		newflags &= ~VM_ACCOUNT;
 	}
 
-	vma = vma_modify_flags(vmi, *pprev, vma, start, end, newflags);
+	vma = vma_modify_flags(vmi, *pprev, vma, start, end, &newflags);
 	if (IS_ERR(vma)) {
 		error = PTR_ERR(vma);
 		goto fail;
diff --git a/mm/mseal.c b/mm/mseal.c
index e5b205562d2ecc..ae442683c5c0dd 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -66,12 +66,13 @@ static int mseal_apply(struct mm_struct *mm,
 		prev = vma;
 
 	for_each_vma_range(vmi, vma, end) {
-		unsigned long curr_end = MIN(vma->vm_end, end);
+		const unsigned long curr_end = MIN(vma->vm_end, end);
 
 		if (!(vma->vm_flags & VM_SEALED)) {
-			vma = vma_modify_flags(&vmi, prev, vma,
-					curr_start, curr_end,
-					vma->vm_flags | VM_SEALED);
+			vm_flags_t vm_flags = vma->vm_flags | VM_SEALED;
+
+			vma = vma_modify_flags(&vmi, prev, vma, curr_start,
+					       curr_end, &vm_flags);
 			if (IS_ERR(vma))
 				return PTR_ERR(vma);
 			vm_flags_set(vma, VM_SEALED);
diff --git a/mm/vma.c b/mm/vma.c
index 0c5e391fe2e2f7..47469c036a72b6 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1638,25 +1638,35 @@ static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg)
 	return vma;
 }
 
-struct vm_area_struct *vma_modify_flags(
-	struct vma_iterator *vmi, struct vm_area_struct *prev,
-	struct vm_area_struct *vma, unsigned long start, unsigned long end,
-	vm_flags_t vm_flags)
+struct vm_area_struct *vma_modify_flags(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		vm_flags_t *vm_flags_ptr)
 {
 	VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);
+	const vm_flags_t vm_flags = *vm_flags_ptr;
+	struct vm_area_struct *ret;
 
 	vmg.vm_flags = vm_flags;
 
-	return vma_modify(&vmg);
+	ret = vma_modify(&vmg);
+	if (IS_ERR(ret))
+		return ret;
+
+	/*
+	 * For a merge to succeed, the flags must match those requested. For
+	 * flags which do not obey typical merge rules (i.e. do not need to
+	 * match), we must let the caller know about them.
+	 */
+	if (vmg.state == VMA_MERGE_SUCCESS)
+		*vm_flags_ptr = ret->vm_flags;
+	return ret;
 }
 
-struct vm_area_struct
-*vma_modify_name(struct vma_iterator *vmi,
-		       struct vm_area_struct *prev,
-		       struct vm_area_struct *vma,
-		       unsigned long start,
-		       unsigned long end,
-		       struct anon_vma_name *new_name)
+struct vm_area_struct *vma_modify_name(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		struct anon_vma_name *new_name)
 {
 	VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);
 
@@ -1665,12 +1675,10 @@ struct vm_area_struct
 	return vma_modify(&vmg);
 }
 
-struct vm_area_struct
-*vma_modify_policy(struct vma_iterator *vmi,
-		   struct vm_area_struct *prev,
-		   struct vm_area_struct *vma,
-		   unsigned long start, unsigned long end,
-		   struct mempolicy *new_pol)
+struct vm_area_struct *vma_modify_policy(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		struct mempolicy *new_pol)
 {
 	VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);
 
@@ -1679,14 +1687,10 @@ struct vm_area_struct
 	return vma_modify(&vmg);
 }
 
-struct vm_area_struct
-*vma_modify_flags_uffd(struct vma_iterator *vmi,
-		       struct vm_area_struct *prev,
-		       struct vm_area_struct *vma,
-		       unsigned long start, unsigned long end,
-		       vm_flags_t vm_flags,
-		       struct vm_userfaultfd_ctx new_ctx,
-		       bool give_up_on_oom)
+struct vm_area_struct *vma_modify_flags_uffd(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end, vm_flags_t vm_flags,
+		struct vm_userfaultfd_ctx new_ctx, bool give_up_on_oom)
 {
 	VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);
 
diff --git a/mm/vma.h b/mm/vma.h
index e912d42c428a57..75f1d9c7204bc5 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -263,47 +263,115 @@ void remove_vma(struct vm_area_struct *vma);
 void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct vm_area_struct *next);
 
-/* We are about to modify the VMA's flags. */
-__must_check struct vm_area_struct
-*vma_modify_flags(struct vma_iterator *vmi,
+/**
+ * vma_modify_flags() - Peform any necessary split/merge in preparation for
+ * setting VMA flags to *@vm_flags in the range @start to @end contained within
+ * @vma.
+ * @vmi: Valid VMA iterator positioned at @vma.
+ * @prev: The VMA immediately prior to @vma or NULL if @vma is the first.
+ * @vma: The VMA containing the range @start to @end to be updated.
+ * @start: The start of the range to update. May be offset within @vma.
+ * @end: The exclusive end of the range to update, may be offset within @vma.
+ * @vm_flags_ptr: A pointer to the VMA flags that the @start to @end range is
+ * about to be set to. On merge, this will be updated to include any additional
+ * flags which remain in place.
+ *
+ * IMPORTANT: The actual modification being requested here is NOT applied,
+ * rather the VMA is perhaps split, perhaps merged to accommodate the change,
+ * and the caller is expected to perform the actual modification.
+ *
+ * In order to account for VMA flags which may persist (e.g. soft-dirty), the
+ * @vm_flags_ptr parameter points to the requested flags which are then updated
+ * so the caller, should they overwrite any existing flags, correctly retains
+ * these.
+ *
+ * Returns: A VMA which contains the range @start to @end ready to have its
+ * flags altered to *@vm_flags.
+ */
+__must_check struct vm_area_struct *vma_modify_flags(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		vm_flags_t *vm_flags_ptr);
+
+/**
+ * vma_modify_name() - Peform any necessary split/merge in preparation for
+ * setting anonymous VMA name to @new_name in the range @start to @end contained
+ * within @vma.
+ * @vmi: Valid VMA iterator positioned at @vma.
+ * @prev: The VMA immediately prior to @vma or NULL if @vma is the first.
+ * @vma: The VMA containing the range @start to @end to be updated.
+ * @start: The start of the range to update. May be offset within @vma.
+ * @end: The exclusive end of the range to update, may be offset within @vma.
+ * @new_name: The anonymous VMA name that the @start to @end range is about to
+ * be set to.
+ *
+ * IMPORTANT: The actual modification being requested here is NOT applied,
+ * rather the VMA is perhaps split, perhaps merged to accommodate the change,
+ * and the caller is expected to perform the actual modification.
+ *
+ * Returns: A VMA which contains the range @start to @end ready to have its
+ * anonymous VMA name changed to @new_name.
+ */
+__must_check struct vm_area_struct *vma_modify_name(struct vma_iterator *vmi,
 		struct vm_area_struct *prev, struct vm_area_struct *vma,
 		unsigned long start, unsigned long end,
-		vm_flags_t vm_flags);
-
-/* We are about to modify the VMA's anon_name. */
-__must_check struct vm_area_struct
-*vma_modify_name(struct vma_iterator *vmi,
-		 struct vm_area_struct *prev,
-		 struct vm_area_struct *vma,
-		 unsigned long start,
-		 unsigned long end,
-		 struct anon_vma_name *new_name);
-
-/* We are about to modify the VMA's memory policy. */
-__must_check struct vm_area_struct
-*vma_modify_policy(struct vma_iterator *vmi,
-		   struct vm_area_struct *prev,
-		   struct vm_area_struct *vma,
+		struct anon_vma_name *new_name);
+
+/**
+ * vma_modify_policy() - Peform any necessary split/merge in preparation for
+ * setting NUMA policy to @new_pol in the range @start to @end contained
+ * within @vma.
+ * @vmi: Valid VMA iterator positioned at @vma.
+ * @prev: The VMA immediately prior to @vma or NULL if @vma is the first.
+ * @vma: The VMA containing the range @start to @end to be updated.
+ * @start: The start of the range to update. May be offset within @vma.
+ * @end: The exclusive end of the range to update, may be offset within @vma.
+ * @new_pol: The NUMA policy that the @start to @end range is about to be set
+ * to.
+ *
+ * IMPORTANT: The actual modification being requested here is NOT applied,
+ * rather the VMA is perhaps split, perhaps merged to accommodate the change,
+ * and the caller is expected to perform the actual modification.
+ *
+ * Returns: A VMA which contains the range @start to @end ready to have its
+ * NUMA policy changed to @new_pol.
+ */
+__must_check struct vm_area_struct *vma_modify_policy(struct vma_iterator *vmi,
+		   struct vm_area_struct *prev, struct vm_area_struct *vma,
 		   unsigned long start, unsigned long end,
 		   struct mempolicy *new_pol);
 
-/* We are about to modify the VMA's flags and/or uffd context. */
-__must_check struct vm_area_struct
-*vma_modify_flags_uffd(struct vma_iterator *vmi,
-		       struct vm_area_struct *prev,
-		       struct vm_area_struct *vma,
-		       unsigned long start, unsigned long end,
-		       vm_flags_t vm_flags,
-		       struct vm_userfaultfd_ctx new_ctx,
-		       bool give_up_on_oom);
-
-__must_check struct vm_area_struct
-*vma_merge_new_range(struct vma_merge_struct *vmg);
-
-__must_check struct vm_area_struct
-*vma_merge_extend(struct vma_iterator *vmi,
-		  struct vm_area_struct *vma,
-		  unsigned long delta);
+/**
+ * vma_modify_flags_uffd() - Peform any necessary split/merge in preparation for
+ * setting VMA flags to @vm_flags and UFFD context to @new_ctx in the range
+ * @start to @end contained within @vma.
+ * @vmi: Valid VMA iterator positioned at @vma.
+ * @prev: The VMA immediately prior to @vma or NULL if @vma is the first.
+ * @vma: The VMA containing the range @start to @end to be updated.
+ * @start: The start of the range to update. May be offset within @vma.
+ * @end: The exclusive end of the range to update, may be offset within @vma.
+ * @vm_flags: The VMA flags that the @start to @end range is about to be set to.
+ * @new_ctx: The userfaultfd context that the @start to @end range is about to
+ * be set to.
+ * @give_up_on_oom: If an out of memory condition occurs on merge, simply give
+ * up on it and treat the merge as best-effort.
+ *
+ * IMPORTANT: The actual modification being requested here is NOT applied,
+ * rather the VMA is perhaps split, perhaps merged to accommodate the change,
+ * and the caller is expected to perform the actual modification.
+ *
+ * Returns: A VMA which contains the range @start to @end ready to have its VMA
+ * flags changed to @vm_flags and its userfaultfd context changed to @new_ctx.
+ */
+__must_check struct vm_area_struct *vma_modify_flags_uffd(struct vma_iterator *vmi,
+		struct vm_area_struct *prev, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end, vm_flags_t vm_flags,
+		struct vm_userfaultfd_ctx new_ctx, bool give_up_on_oom);
+
+__must_check struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg);
+
+__must_check struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
+		  struct vm_area_struct *vma, unsigned long delta);
 
 void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb);
 
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index 656e1c75b711e5..fd37ce3b262808 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -339,6 +339,7 @@ static bool test_simple_modify(void)
 	struct mm_struct mm = {};
 	struct vm_area_struct *init_vma = alloc_vma(&mm, 0, 0x3000, 0, vm_flags);
 	VMA_ITERATOR(vmi, &mm, 0x1000);
+	vm_flags_t flags = VM_READ | VM_MAYREAD;
 
 	ASSERT_FALSE(attach_vma(&mm, init_vma));
 
@@ -347,7 +348,7 @@ static bool test_simple_modify(void)
 	 * performs the merge/split only.
 	 */
 	vma = vma_modify_flags(&vmi, init_vma, init_vma,
-			       0x1000, 0x2000, VM_READ | VM_MAYREAD);
+			       0x1000, 0x2000, &flags);
 	ASSERT_NE(vma, NULL);
 	/* We modify the provided VMA, and on split allocate new VMAs. */
 	ASSERT_EQ(vma, init_vma);