Documentation/arch/riscv/vm-layout.rst

   1 .. SPDX-License-Identifier: GPL-2.0
   2
   3 =====================================
   4 Virtual Memory Layout on RISC-V Linux
   5 =====================================
   6
   7 :Author: Alexandre Ghiti <alex@ghiti.fr>
   8 :Date: 12 February 2021
   9
  10 This document describes the virtual memory layout used by the RISC-V Linux
  11 Kernel.
  12
  13 RISC-V Linux Kernel 32bit
  14 =========================
  15
  16 RISC-V Linux Kernel SV32
  17 ------------------------
  18
  19 TODO
  20
  21 RISC-V Linux Kernel 64bit
  22 =========================
  23
  24 The RISC-V privileged architecture document states that the 64bit addresses
  25 "must have bits 63–48 all equal to bit 47, or else a page-fault exception will
  26 occur.": that splits the virtual address space into 2 halves separated by a very
  27 big hole, the lower half is where the userspace resides, the upper half is where
  28 the RISC-V Linux Kernel resides.
  29
  30 RISC-V Linux Kernel SV39
  31 ------------------------
  32
  33 ::
  34
  35   ========================================================================================================================
  36       Start addr    |   Offset   |     End addr     |  Size   | VM area description
  37   ========================================================================================================================
  38                     |            |                  |         |
  39    0000000000000000 |    0       | 0000003fffffffff |  256 GB | user-space virtual memory, different per mm
  40   __________________|____________|__________________|_________|___________________________________________________________
  41                     |            |                  |         |
  42    0000004000000000 | +256    GB | ffffffbfffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
  43                     |            |                  |         |     virtual memory addresses up to the -256 GB
  44                     |            |                  |         |     starting offset of kernel mappings.
  45   __________________|____________|__________________|_________|___________________________________________________________
  46                                                               |
  47                                                               | Kernel-space virtual memory, shared between all processes:
  48   ____________________________________________________________|___________________________________________________________
  49                     |            |                  |         |
  50    ffffffc4fea00000 | -236    GB | ffffffc4feffffff |    6 MB | fixmap
  51    ffffffc4ff000000 | -236    GB | ffffffc4ffffffff |   16 MB | PCI io
  52    ffffffc500000000 | -236    GB | ffffffc5ffffffff |    4 GB | vmemmap
  53    ffffffc600000000 | -232    GB | ffffffd5ffffffff |   64 GB | vmalloc/ioremap space
  54    ffffffd600000000 | -168    GB | fffffff5ffffffff |  128 GB | direct mapping of all physical memory
  55                     |            |                  |         |
  56    fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
  57   __________________|____________|__________________|_________|____________________________________________________________
  58                                                               |
  59                                                               |
  60   ____________________________________________________________|____________________________________________________________
  61                     |            |                  |         |
  62    ffffffff00000000 |   -4    GB | ffffffff7fffffff |    2 GB | modules, BPF
  63    ffffffff80000000 |   -2    GB | ffffffffffffffff |    2 GB | kernel
  64   __________________|____________|__________________|_________|____________________________________________________________
  65
  66
  67 RISC-V Linux Kernel SV48
  68 ------------------------
  69
  70 ::
  71
  72  ========================================================================================================================
  73       Start addr    |   Offset   |     End addr     |  Size   | VM area description
  74  ========================================================================================================================
  75                     |            |                  |         |
  76    0000000000000000 |    0       | 00007fffffffffff |  128 TB | user-space virtual memory, different per mm
  77   __________________|____________|__________________|_________|___________________________________________________________
  78                     |            |                  |         |
  79    0000800000000000 | +128    TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
  80                     |            |                  |         | virtual memory addresses up to the -128 TB
  81                     |            |                  |         | starting offset of kernel mappings.
  82   __________________|____________|__________________|_________|___________________________________________________________
  83                                                               |
  84                                                               | Kernel-space virtual memory, shared between all processes:
  85   ____________________________________________________________|___________________________________________________________
  86                     |            |                  |         |
  87    ffff8d7ffea00000 |  -114.5 TB | ffff8d7ffeffffff |    6 MB | fixmap
  88    ffff8d7fff000000 |  -114.5 TB | ffff8d7fffffffff |   16 MB | PCI io
  89    ffff8d8000000000 |  -114.5 TB | ffff8f7fffffffff |    2 TB | vmemmap
  90    ffff8f8000000000 |  -112.5 TB | ffffaf7fffffffff |   32 TB | vmalloc/ioremap space
  91    ffffaf8000000000 |  -80.5  TB | ffffef7fffffffff |   64 TB | direct mapping of all physical memory
  92    ffffef8000000000 |  -16.5  TB | fffffffeffffffff | 16.5 TB | kasan
  93   __________________|____________|__________________|_________|____________________________________________________________
  94                                                               |
  95                                                               | Identical layout to the 39-bit one from here on:
  96   ____________________________________________________________|____________________________________________________________
  97                     |            |                  |         |
  98    ffffffff00000000 |   -4    GB | ffffffff7fffffff |    2 GB | modules, BPF
  99    ffffffff80000000 |   -2    GB | ffffffffffffffff |    2 GB | kernel
 100   __________________|____________|__________________|_________|____________________________________________________________
 101
 102
 103 RISC-V Linux Kernel SV57
 104 ------------------------
 105
 106 ::
 107
 108  ========================================================================================================================
 109       Start addr    |   Offset   |     End addr     |  Size   | VM area description
 110  ========================================================================================================================
 111                     |            |                  |         |
 112    0000000000000000 |   0        | 00ffffffffffffff |   64 PB | user-space virtual memory, different per mm
 113   __________________|____________|__________________|_________|___________________________________________________________
 114                     |            |                  |         |
 115    0100000000000000 | +64     PB | feffffffffffffff | ~16K PB | ... huge, almost 64 bits wide hole of non-canonical
 116                     |            |                  |         | virtual memory addresses up to the -64 PB
 117                     |            |                  |         | starting offset of kernel mappings.
 118   __________________|____________|__________________|_________|___________________________________________________________
 119                                                               |
 120                                                               | Kernel-space virtual memory, shared between all processes:
 121   ____________________________________________________________|___________________________________________________________
 122                     |            |                  |         |
 123    ff1bfffffea00000 | -57     PB | ff1bfffffeffffff |    6 MB | fixmap
 124    ff1bffffff000000 | -57     PB | ff1bffffffffffff |   16 MB | PCI io
 125    ff1c000000000000 | -57     PB | ff1fffffffffffff |    1 PB | vmemmap
 126    ff20000000000000 | -56     PB | ff5fffffffffffff |   16 PB | vmalloc/ioremap space
 127    ff60000000000000 | -40     PB | ffdeffffffffffff |   32 PB | direct mapping of all physical memory
 128    ffdf000000000000 |  -8     PB | fffffffeffffffff |    8 PB | kasan
 129   __________________|____________|__________________|_________|____________________________________________________________
 130                                                               |
 131                                                               | Identical layout to the 39-bit one from here on:
 132   ____________________________________________________________|____________________________________________________________
 133                     |            |                  |         |
 134    ffffffff00000000 |  -4     GB | ffffffff7fffffff |    2 GB | modules, BPF
 135    ffffffff80000000 |  -2     GB | ffffffffffffffff |    2 GB | kernel
 136   __________________|____________|__________________|_________|____________________________________________________________