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Linux/Documentation/arch/riscv/vm-layout.rst

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  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   __________________|____________|__________________|_________|____________________________________________________________

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