svn commit: r342144 - head/share/man/man9

[Konstantin Belousov]

Author: kib
Date: Sun Dec 16 01:51:38 2018
New Revision: 342144
URL: https://svnweb.freebsd.org/changeset/base/342144

Log:
  Document new required MI behaviour of pmap_enter(9) for CoW.
  
  Reviewed by:	markj
  MFC after:	3 days
  Sponsored by:	The FreeBSD Foundation
  Differential revision:	https://reviews.freebsd.org/D18568

Modified:
  head/share/man/man9/pmap_enter.9

Modified: head/share/man/man9/pmap_enter.9
==============================================================================
--- head/share/man/man9/pmap_enter.9	Sun Dec 16 01:19:10 2018	(r342143)
+++ head/share/man/man9/pmap_enter.9	Sun Dec 16 01:51:38 2018	(r342144)
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 16, 2018
+.Dd December 16, 2018
 .Dt PMAP_ENTER 9
 .Os
 .Sh NAME
@@ -119,6 +119,14 @@ It is advised to clear
 for destroyed mappings if the implementation can ensure
 that no other writeable managed mappings for the previously
 mapped pages exist.
+.Pp
+If the request modifies an existing mapping to use a different physical
+page, an implementation of
+.Nm
+must invalidate the 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