linux-kernel - [PATCH] mremap.2: Add information for MREMAP

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Message-Id: <20200207202124.68949-1-bgeffon@google.com>
Date:   Fri,  7 Feb 2020 12:21:24 -0800
From:   Brian Geffon <bgeffon@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Will Deacon <will@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: [PATCH] mremap.2: Add information for MREMAP_DONTUNMAP.

Signed-off-by: Brian Geffon <bgeffon@...gle.com>
---
 man2/mremap.2 | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/man2/mremap.2 b/man2/mremap.2
index d73fb64fa..c660a45be 100644
--- a/man2/mremap.2
+++ b/man2/mremap.2
@@ -26,7 +26,8 @@
 .\" 1996-04-12 Tom Bjorkholm <tomb@...ata.se>
 .\"            Update for Linux 1.3.87 and later
 .\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
-.\"
+.\" 2020-02-05 Brian Geffon <bgeffon@...gle.com>
+.\"            Update for MREMAP_DONTUNMAP.
 .TH MREMAP 2 2019-03-06 "Linux" "Linux Programmer's Manual"
 .SH NAME
 mremap \- remap a virtual memory address
@@ -129,6 +130,13 @@ If
 is specified, then
 .B MREMAP_MAYMOVE
 must also be specified.
+.TP
+.BR MREMAP_DONTUNMAP " (since Linux ?.?)"
+This flag which must be used in conjuction with
+.B MREMAP_MAYMOVE
+remaps a mapping to a new address and it does not unmap the mapping at \fIold_address\fP. This flag can only be used with private anonymous mappings. Any access to the range specified at \fIold_address\fP after completion will result in a page fault. If a
+.BR userfaultfd (2)
+was registered on the mapping specified by \fIold_address\fP it will continue to watch that mapping for faults.
 .PP
 If the memory segment specified by
 .I old_address
@@ -176,6 +184,8 @@ a value other than
 .B MREMAP_MAYMOVE
 or
 .B MREMAP_FIXED
+or
+.B MREMAP_DONTUNMAP
 was specified in
 .IR flags ;
 .IP *
@@ -197,9 +207,14 @@ and
 .IR old_size ;
 .IP *
 .B MREMAP_FIXED
+or
+.B MREMAP_DONTUNMAP
 was specified without also specifying
 .BR MREMAP_MAYMOVE ;
 .IP *
+.B MREMAP_DONTUNMAP
+was specified with an \fIold_address\fP that was not private anonymous;
+.IP *
 \fIold_size\fP was zero and \fIold_address\fP does not refer to a
 shareable mapping (but see BUGS);
 .IP *
@@ -209,10 +224,20 @@ flag was not specified.
 .RE
 .TP
 .B ENOMEM
+Not enough memory was available to complete the operation.
+Possible causes are:
+.RS
+.IP * 3
 The memory area cannot be expanded at the current virtual address, and the
 .B MREMAP_MAYMOVE
 flag is not set in \fIflags\fP.
 Or, there is not enough (virtual) memory available.
+.IP *
+.B MREMAP_DONTUNMAP
+was used without
+.B MREMAP_FIXED
+causing a new mapping to be created that would exceed the virtual memory available or it would exceed the maximum number of allowed mappings.
+.RE
 .SH CONFORMING TO
 This call is Linux-specific, and should not be used in programs
 intended to be portable.
-- 
2.25.0.341.g760bfbb309-goog