linux_memutils

Module iomem

Source
Expand description

Parsing of the physical memory map provided by /proc/iomem.

The /proc/iomem file exposes the kernel’s resource tree and thus a map of physical memory to user space, making it very useful for gracefully reading specific regions of memory from /dev/mem.

§Background

The Linux kernel maintains a resource tree with the memory address ranges allocated to every resource (RAM, devices, and so on).

The first additions to this tree are made during early boot when the system firmware supplies its initial memory map to the kernel via E820 (BIOS) or GetMemoryMap() (UEFI). The kernel will practically always modify this map further (based on known quirks or custom memmap overrides, for instance) before registering its specified memory regions in the tree.

Additional address ranges are allocated for device MMIO, so the tree will contain not just entries for the above memory map (with ACPI Address Range Types such as Reserved) but also more arbitrarily named devices (such as IOAPIC 0 or PCI Bus <ID>).

§Excerpt of /proc/iomem

Notice how the address range names include both human-readable ACPI types and MMIO devices.

00000000-00000fff : Reserved            // Real-Mode Address Space (< 1 MiB)
00001000-0009efff : System RAM
0009f000-0009ffff : Reserved
000e0000-000fffff : Reserved
  000a0000-000effff : PCI Bus 0000:00
  000f0000-000fffff : System ROM
00100000-09bfffff : System RAM          // Extended Memory (> 1 MiB)
[~]
cad7e000-cbd7dfff : ACPI Non-volatile Storage
  cbc37000-cbc37fff : USBC000:00
cbd7e000-cbdfdfff : ACPI Tables
[~]
fc000000-fdffffff : PCI Bus 0000:00
  [~ Other devices on the PCIe bus ~]
  fd900000-fd9fffff : PCI Bus 0000:01
    fd900000-fd903fff : 0000:01:00.0
      fd900000-fd903fff : nvme
  fdf00000-fdf7ffff : amd_iommu
feb00000-feb00007 : SB800 TCO
fec00000-fec003ff : IOAPIC 0
[~]
100000000-72e2fffff : System RAM
  38a400000-38b7fffff : Kernel code
  38b800000-38c532fff : Kernel rodata
  38c600000-38c88cf7f : Kernel data
  38d20e000-38d5fffff : Kernel bss

Structs§

MemoryRegion
A region in physical memory as indicated in the memory map.

Enums§

MemoryRegionType
The types of memory address ranges distinguished by the kernel.
ParseError

Functions§

parse_iomem_map
Parse the given iomem-style memory map to a vector of MemoryRegions.
parse_proc_iomem
Directly read and parse /proc/iomem to a vector of MemoryRegions.