userfaultfd: add userfaultfd_wp mm helpers

These helpers will be used to know if to call handle_userfault() during
wrprotect faults in order to deliver the wrprotect faults to userland.

include/linux/userfaultfd_k.h

@@ -65,6 +65,11 @@ static inline bool userfaultfd_missing(struct vm_area_struct *vma)
 	return vma->vm_flags & VM_UFFD_MISSING;
 }
 
+static inline bool userfaultfd_wp(struct vm_area_struct *vma)
+{
+	return vma->vm_flags & VM_UFFD_WP;
+}
+
 static inline bool userfaultfd_armed(struct vm_area_struct *vma)
 {
 	return vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP);
@@ -92,6 +97,11 @@ static inline bool userfaultfd_missing(struct vm_area_struct *vma)
 	return false;
 }
 
+static inline bool userfaultfd_wp(struct vm_area_struct *vma)
+{
+	return false;
+}
+
 static inline bool userfaultfd_armed(struct vm_area_struct *vma)
 {
 	return false;