Index: share/man/man9/pmap_enter.9
===================================================================
--- share/man/man9/pmap_enter.9
+++ share/man/man9/pmap_enter.9
@@ -120,6 +120,14 @@
 that no other writeable managed mappings for the previously
 mapped pages exist.
 .Pp
+If the request modifies existing mapping to use different physical
+page, an implementation of
+.Nm
+must invalidate previous mapping before installing the new one.
+This ensures that all threads sharing the pmap keep a consistent
+view of the mapping, which is necessary for the correct handling
+of CoW (copy on write) faults.
+.Pp
 If the page
 .Fa m
 is managed, the page must be busied by the caller