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1.. SPDX-License-Identifier: GPL-2.0
2
3=====================================
4Virtual Memory Layout on RISC-V Linux
5=====================================
6
7:Author: Alexandre Ghiti <alex@ghiti.fr>
8:Date: 12 February 2021
9
10This document describes the virtual memory layout used by the RISC-V Linux
11Kernel.
12
13RISC-V Linux Kernel 32bit
14=========================
15
16RISC-V Linux Kernel SV32
17------------------------
18
19TODO
20
21RISC-V Linux Kernel 64bit
22=========================
23
24The 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
26occur.": that splits the virtual address space into 2 halves separated by a very
27big hole, the lower half is where the userspace resides, the upper half is where
28the RISC-V Linux Kernel resides.
29
30RISC-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
67RISC-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
103RISC-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 __________________|____________|__________________|_________|____________________________________________________________