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+.\"	$OpenBSD: mem.4,v 1.7 2024/03/22 12:29:33 jsg Exp $
+.\"
+.\" Copyright (c) 1991 The Regents of the University of California.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	from: @(#)mem.4	5.3 (Berkeley) 5/2/91
+.\"
+.Dd $Mdocdate: March 22 2024 $
+.Dt MEM 4 amd64
+.Os
+.Sh NAME
+.Nm mem ,
+.Nm kmem
+.Nd memory files
+.Sh DESCRIPTION
+The special file
+.Pa /dev/mem
+is an interface to the physical memory of the computer.
+Byte offsets in this file are interpreted as physical memory addresses.
+Reading and writing this file is equivalent to reading and writing
+memory itself.
+Only offsets within the bounds of
+.Pa /dev/mem
+are allowed.
+.Pp
+Kernel virtual memory is accessed through the interface
+.Pa /dev/kmem
+in the same manner as
+.Pa /dev/mem .
+Only kernel virtual addresses that are currently mapped to memory are allowed.
+.Pp
+On amd64, physical memory is discontiguous; especially,
+the ISA I/O memory space covers the physical address range from
+.Li 0x000a0000
+to
+.Li 0x00100000 .
+.Pp
+The kernel virtual memory begins at address
+.Li 0xffffffff80000000 .
+.Pp
+Even with sufficient file system permissions,
+these devices can only be opened when the
+.Xr securelevel 7
+is insecure or when the
+.Va kern.allowkmem
+.Xr sysctl 2
+variable is set.
+.Sh FILES
+.Bl -tag -width Pa -compact
+.It Pa /dev/mem
+.It Pa /dev/kmem
+.El
+.Sh SEE ALSO
+.Xr mtrr 4 ,
+.Xr securelevel 7
+.Sh HISTORY
+The
+.Pa /dev/mem
+file appeared in
+.At v1 ,
+.Pa /dev/kmem
+appeared in
+.At v5 .