1.\" Copyright (c) 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)mem.4 5.3 (Berkeley) 5/2/91 29.\" $FreeBSD$ 30.\" 31.Dd August 25, 2020 32.Dt MEM 4 33.Os 34.Sh NAME 35.Nm mem , 36.Nm kmem 37.Nd memory files 38.Sh SYNOPSIS 39.Cd "device mem" 40.Sh DESCRIPTION 41The special file 42.Pa /dev/mem 43is an interface to the physical memory of the computer. 44Byte offsets in this file are interpreted as physical memory addresses. 45Reading and writing this file is equivalent to reading and writing 46memory itself. 47Only offsets within the bounds of 48.Pa /dev/mem 49are allowed. 50.Pp 51Kernel virtual memory is accessed through the interface 52.Pa /dev/kmem 53in the same manner as 54.Pa /dev/mem . 55Only kernel virtual addresses that are currently mapped to memory are allowed. 56.Pp 57On ISA the I/O memory space begins at physical address 0x000a0000 58and runs to 0x00100000. 59The 60per-process data 61size 62for the current process 63is 64.Dv UPAGES 65long, and ends at virtual 66address 0xf0000000. 67.Sh IOCTL INTERFACE 68The 69.Dv MEM_EXTRACT_PADDR 70ioctl can be used to look up the physical address and NUMA domain of a given 71virtual address in the calling process' address space. 72The request is described by 73.Bd -literal 74struct mem_extract { 75 uint64_t me_vaddr; /* input */ 76 uint64_t me_paddr; /* output */ 77 int me_domain; /* output */ 78 int me_state; /* output */ 79}; 80.Ed 81.Pp 82The ioctl returns an error if the address is not valid. 83The information returned by 84.Dv MEM_EXTRACT_PADDR 85may be out of date by the time that the ioctl call returns. 86Specifically, concurrent system calls, page faults, or system page reclamation 87activity may have unmapped the virtual page or replaced the backing physical 88page before the ioctl call returns. 89Wired pages, e.g., those locked by 90.Xr mlock 2 , 91will not be reclaimed by the system. 92.Pp 93The 94.Fa me_state 95field provides information about the state of the virtual page: 96.Bl -tag -width indent 97.It Dv ME_STATE_INVALID 98The virtual address is invalid. 99.It Dv ME_STATE_VALID 100The virtual address is valid but is not mapped at the time of the ioctl call. 101.It Dv ME_STATE_MAPPED 102The virtual address corresponds to a physical page mapping, and the 103.Fa me_paddr 104and 105.Fa me_domain 106fields are valid. 107.Pp 108Several architectures allow attributes to be associated with ranges of physical 109memory. 110These attributes can be manipulated via 111.Fn ioctl 112calls performed on 113.Pa /dev/mem . 114Declarations and data types are to be found in 115.In sys/memrange.h . 116.Pp 117The specific attributes, and number of programmable ranges may vary between 118architectures. 119The full set of supported attributes is: 120.Bl -tag -width indent 121.It Dv MDF_UNCACHEABLE 122The region is not cached. 123.It Dv MDF_WRITECOMBINE 124Writes to the region may be combined or performed out of order. 125.It Dv MDF_WRITETHROUGH 126Writes to the region are committed synchronously. 127.It Dv MDF_WRITEBACK 128Writes to the region are committed asynchronously. 129.It Dv MDF_WRITEPROTECT 130The region cannot be written to. 131.El 132.Pp 133Memory ranges are described by 134.Bd -literal 135struct mem_range_desc { 136 uint64_t mr_base; /* physical base address */ 137 uint64_t mr_len; /* physical length of region */ 138 int mr_flags; /* attributes of region */ 139 char mr_owner[8]; 140}; 141.Ed 142.Pp 143In addition to the region attributes listed above, the following flags 144may also be set in the 145.Fa mr_flags 146field: 147.Bl -tag -width indent 148.It MDF_FIXBASE 149The region's base address cannot be changed. 150.It MDF_FIXLEN 151The region's length cannot be changed. 152.It MDF_FIRMWARE 153The region is believed to have been established by the system firmware. 154.It MDF_ACTIVE 155The region is currently active. 156.It MDF_BOGUS 157We believe the region to be invalid or otherwise erroneous. 158.It MDF_FIXACTIVE 159The region cannot be disabled. 160.It MDF_BUSY 161The region is currently owned by another process and may not be 162altered. 163.El 164.Pp 165Operations are performed using 166.Bd -literal 167struct mem_range_op { 168 struct mem_range_desc *mo_desc; 169 int mo_arg[2]; 170}; 171.Ed 172.Pp 173The 174.Dv MEMRANGE_GET 175ioctl is used to retrieve current memory range attributes. 176If 177.Va mo_arg[0] 178is set to 0, it will be updated with the total number of memory range 179descriptors. 180If greater than 0, the array at 181.Va mo_desc 182will be filled with a corresponding number of descriptor structures, 183or the maximum, whichever is less. 184.Pp 185The 186.Dv MEMRANGE_SET 187ioctl is used to add, alter and remove memory range attributes. 188A range 189with the 190.Dv MDF_FIXACTIVE 191flag may not be removed; a range with the 192.Dv MDF_BUSY 193flag may not be removed or updated. 194.Pp 195.Va mo_arg[0] 196should be set to 197.Dv MEMRANGE_SET_UPDATE 198to update an existing or establish a new range, or to 199.Dv MEMRANGE_SET_REMOVE 200to remove a range. 201.El 202.Sh RETURN VALUES 203.Bl -tag -width Er 204.It Bq Er EOPNOTSUPP 205Memory range operations are not supported on this architecture. 206.It Bq Er ENXIO 207No memory range descriptors are available (e.g., firmware has not enabled 208any). 209.It Bq Er EINVAL 210The memory range supplied as an argument is invalid or overlaps another 211range in a fashion not supported by this architecture. 212.It Bq Er EBUSY 213An attempt to remove or update a range failed because the range is busy. 214.It Bq Er ENOSPC 215An attempt to create a new range failed due to a shortage of hardware 216resources (e.g., descriptor slots). 217.It Bq Er ENOENT 218An attempt to remove a range failed because no range matches the descriptor 219base/length supplied. 220.It Bq Er EPERM 221An attempt to remove a range failed because the range is permanently 222enabled. 223.El 224.Sh FILES 225.Bl -tag -width /dev/kmem -compact 226.It Pa /dev/mem 227.It Pa /dev/kmem 228.El 229.Sh SEE ALSO 230.Xr kvm 3 , 231.Xr memcontrol 8 232.Sh HISTORY 233The 234.Nm mem 235and 236.Nm kmem 237files appeared in 238.At v6 . 239The ioctl interface for memory range attributes was added in 240.Fx 3.2 . 241.Sh BUGS 242Busy range attributes are not yet managed correctly. 243.Pp 244This device is required for all users of 245.Xr kvm 3 246to operate. 247