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Document new required MI behaviour of pmap_enter(9) for CoW.

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Reviewed by:	markj
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D18568
This commit is contained in:
Konstantin Belousov 2018-12-16 01:51:38 +00:00
parent 3398cc6839
commit 6b5007c893
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=342144
1 changed files with 9 additions and 1 deletions
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10
share/man/man9/pmap_enter.9
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@ -26,7 +26,7 @@
.\" .\"
.\" $FreeBSD$ .\" $FreeBSD$
.\" .\"
.Dd February 16, 2018 .Dd December 16, 2018
.Dt PMAP_ENTER 9 .Dt PMAP_ENTER 9
.Os .Os
.Sh NAME .Sh NAME
@ -120,6 +120,14 @@ for destroyed mappings if the implementation can ensure
that no other writeable managed mappings for the previously that no other writeable managed mappings for the previously
mapped pages exist. mapped pages exist.
.Pp .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 If the page
.Fa m .Fa m
is managed, the page must be busied by the caller is managed, the page must be busied by the caller