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.Dd $Mdocdate: January 12 2018 $
.Dt MEM 4 hppa
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd memory files and memory controller
.Sh SYNOPSIS
.Cd "mem* at mainbus0 flags 0x0000"
.Sh DESCRIPTION
The
.Nm
driver controls and restricts access to the systems memory
by the hardware buses and the processor.
.Pp
It also provides an interface to userland through the special files
.Pa /dev/mem
and
.Pa /dev/kmem .
Physical memory is accessed through
.Pa /dev/mem ,
while kernel virtual memory is accessed through
.Pa /dev/kmem .
Access to kernel virtual addresses not currently mapped to memory will fail.
On hppa, the physical memory range is always contiguous and starts at
address 0; kernel virtual memory begins at address 0 as well.
.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 /dev/kmem -compact
.It Pa /dev/mem
.It Pa /dev/kmem
.El
.Sh SEE ALSO
.Xr securelevel 7
.Sh CAVEATS
On some systems featuring a
.Dq Viper
memory controller,
.Ox
may not configure bus arbitration correctly, causing the boot process
to freeze during either
.Nm
or
.Xr cpu 4
device probe.
.Pp
In this case, a different initialization strategy can be achieved by
setting
.Ar flags
to 0x0001
.Po
see
.Xr boot_config 8
for details
.Pc .