diff --git a/mm/vma.c b/mm/vma.c
index 1be613044b4a..88ef92ab24ec 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1851,12 +1851,25 @@ struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
 					struct vm_area_struct *vma,
 					unsigned long delta)
 {
-	VMG_VMA_STATE(vmg, vmi, vma, vma, vma->vm_end, vma->vm_end + delta);
+	const unsigned long start =
+		vma_can_merge(vma) ? vma->vm_end : vma->vm_start;
+	VMG_VMA_STATE(vmg, vmi, vma, vma, start, vma->vm_end + delta);
 
-	vmg.next = vma_iter_next_rewind(vmi, NULL);
 	vmg.middle = NULL; /* We use the VMA to populate VMG fields only. */
 
-	return vma_merge_new_range(&vmg);
+	if (vma_can_merge(vma)) {
+		vmg.next = vma_iter_next_rewind(vmi, NULL);
+		return vma_merge_new_range(&vmg);
+	}
+
+	/* Mixed mappings are permitted to be expanded, not merged. */
+	VM_WARN_ON_ONCE(vma_is_fixed_mapping(vma));
+	VM_WARN_ON_ONCE(!vma_test(vma, VMA_MIXEDMAP_BIT));
+	vma_prev(vmi); /* Reposition to start of VMA. */
+	vmg.target = vma;
+	if (vma_expand(&vmg))
+		return NULL;
+	return vma;
 }
 
 void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb)
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index f449129ea97a..e0eab4eca998 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -1727,3 +1727,8 @@ static inline bool vma_flags_can_merge(const vma_flags_t *flags)
 	 */
 	return !vma_flags_is_hugetlb(flags);
 }
+
+static inline bool vma_can_merge(const struct vm_area_struct *vma)
+{
+	return vma_flags_can_merge(&vma->flags);
+}