| blob | f2db178b353f8ef763c2b8bf39cb55406898080a |
1 .. SPDX-License-Identifier: GPL-2.0
3 =================
4 Memory Management
5 =================
7 Complete virtual memory map with 4-level page tables
8 ====================================================
10 .. note::
12 - Negative addresses such as "-23 TB" are absolute addresses in bytes, counted down
13 from the top of the 64-bit address space. It's easier to understand the layout
14 when seen both in absolute addresses and in distance-from-top notation.
16 For example 0xffffe90000000000 == -23 TB, it's 23 TB lower than the top of the
17 64-bit address space (ffffffffffffffff).
19 Note that as we get closer to the top of the address space, the notation changes
20 from TB to GB and then MB/KB.
22 - "16M TB" might look weird at first sight, but it's an easier way to visualize size
23 notation than "16 EB", which few will recognize at first sight as 16 exabytes.
24 It also shows it nicely how incredibly large 64-bit address space is.
26 ::
28 ========================================================================================================================
29 Start addr | Offset | End addr | Size | VM area description
30 ========================================================================================================================
31 | | | |
32 0000000000000000 | 0 | 00007fffffffefff | ~128 TB | user-space virtual memory, different per mm
33 00007ffffffff000 | ~128 TB | 00007fffffffffff | 4 kB | ... guard hole
34 __________________|____________|__________________|_________|___________________________________________________________
35 | | | |
36 0000800000000000 | +128 TB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
37 | | | | virtual memory addresses up to the -8 EB
38 | | | | starting offset of kernel mappings.
39 | | | |
40 | | | | LAM relaxes canonicallity check allowing to create aliases
41 | | | | for userspace memory here.
42 __________________|____________|__________________|_________|___________________________________________________________
43 |
44 | Kernel-space virtual memory, shared between all processes:
45 __________________|____________|__________________|_________|___________________________________________________________
46 | | | |
47 8000000000000000 | -8 EB | ffff7fffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
48 | | | | virtual memory addresses up to the -128 TB
49 | | | | starting offset of kernel mappings.
50 | | | |
51 | | | | LAM_SUP relaxes canonicallity check allowing to create
52 | | | | aliases for kernel memory here.
53 ____________________________________________________________|___________________________________________________________
54 | | | |
55 ffff800000000000 | -128 TB | ffff87ffffffffff | 8 TB | ... guard hole, also reserved for hypervisor
56 ffff880000000000 | -120 TB | ffff887fffffffff | 0.5 TB | LDT remap for PTI
57 ffff888000000000 | -119.5 TB | ffffc87fffffffff | 64 TB | direct mapping of all physical memory (page_offset_base)
58 ffffc88000000000 | -55.5 TB | ffffc8ffffffffff | 0.5 TB | ... unused hole
59 ffffc90000000000 | -55 TB | ffffe8ffffffffff | 32 TB | vmalloc/ioremap space (vmalloc_base)
60 ffffe90000000000 | -23 TB | ffffe9ffffffffff | 1 TB | ... unused hole
61 ffffea0000000000 | -22 TB | ffffeaffffffffff | 1 TB | virtual memory map (vmemmap_base)
62 ffffeb0000000000 | -21 TB | ffffebffffffffff | 1 TB | ... unused hole
63 ffffec0000000000 | -20 TB | fffffbffffffffff | 16 TB | KASAN shadow memory
64 __________________|____________|__________________|_________|____________________________________________________________
65 |
66 | Identical layout to the 56-bit one from here on:
67 ____________________________________________________________|____________________________________________________________
68 | | | |
69 fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole
70 | | | | vaddr_end for KASLR
71 fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping
72 fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | ... unused hole
73 ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks
74 ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole
75 ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space
76 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole
77 ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0
78 ffffffff80000000 |-2048 MB | | |
79 ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space
80 ffffffffff000000 | -16 MB | | |
81 FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset
82 ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI
83 ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole
84 __________________|____________|__________________|_________|___________________________________________________________
87 Complete virtual memory map with 5-level page tables
88 ====================================================
90 .. note::
92 - With 56-bit addresses, user-space memory gets expanded by a factor of 512x,
93 from 0.125 PB to 64 PB. All kernel mappings shift down to the -64 PB starting
94 offset and many of the regions expand to support the much larger physical
95 memory supported.
97 ::
99 ========================================================================================================================
100 Start addr | Offset | End addr | Size | VM area description
101 ========================================================================================================================
102 | | | |
103 0000000000000000 | 0 | 00fffffffffff000 | ~64 PB | user-space virtual memory, different per mm
104 00fffffffffff000 | ~64 PB | 00ffffffffffffff | 4 kB | ... guard hole
105 __________________|____________|__________________|_________|___________________________________________________________
106 | | | |
107 0100000000000000 | +64 PB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
108 | | | | virtual memory addresses up to the -8EB TB
109 | | | | starting offset of kernel mappings.
110 | | | |
111 | | | | LAM relaxes canonicallity check allowing to create aliases
112 | | | | for userspace memory here.
113 __________________|____________|__________________|_________|___________________________________________________________
114 |
115 | Kernel-space virtual memory, shared between all processes:
116 ____________________________________________________________|___________________________________________________________
117 8000000000000000 | -8 EB | feffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
118 | | | | virtual memory addresses up to the -64 PB
119 | | | | starting offset of kernel mappings.
120 | | | |
121 | | | | LAM_SUP relaxes canonicallity check allowing to create
122 | | | | aliases for kernel memory here.
123 ____________________________________________________________|___________________________________________________________
124 | | | |
125 ff00000000000000 | -64 PB | ff0fffffffffffff | 4 PB | ... guard hole, also reserved for hypervisor
126 ff10000000000000 | -60 PB | ff10ffffffffffff | 0.25 PB | LDT remap for PTI
127 ff11000000000000 | -59.75 PB | ff90ffffffffffff | 32 PB | direct mapping of all physical memory (page_offset_base)
128 ff91000000000000 | -27.75 PB | ff9fffffffffffff | 3.75 PB | ... unused hole
129 ffa0000000000000 | -24 PB | ffd1ffffffffffff | 12.5 PB | vmalloc/ioremap space (vmalloc_base)
130 ffd2000000000000 | -11.5 PB | ffd3ffffffffffff | 0.5 PB | ... unused hole
131 ffd4000000000000 | -11 PB | ffd5ffffffffffff | 0.5 PB | virtual memory map (vmemmap_base)
132 ffd6000000000000 | -10.5 PB | ffdeffffffffffff | 2.25 PB | ... unused hole
133 ffdf000000000000 | -8.25 PB | fffffbffffffffff | ~8 PB | KASAN shadow memory
134 __________________|____________|__________________|_________|____________________________________________________________
135 |
136 | Identical layout to the 47-bit one from here on:
137 ____________________________________________________________|____________________________________________________________
138 | | | |
139 fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole
140 | | | | vaddr_end for KASLR
141 fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping
142 fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | ... unused hole
143 ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks
144 ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole
145 ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space
146 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole
147 ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0
148 ffffffff80000000 |-2048 MB | | |
149 ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space
150 ffffffffff000000 | -16 MB | | |
151 FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset
152 ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI
153 ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole
154 __________________|____________|__________________|_________|___________________________________________________________
156 Architecture defines a 64-bit virtual address. Implementations can support
157 less. Currently supported are 48- and 57-bit virtual addresses. Bits 63
158 through to the most-significant implemented bit are sign extended.
159 This causes hole between user space and kernel addresses if you interpret them
160 as unsigned.
162 The direct mapping covers all memory in the system up to the highest
163 memory address (this means in some cases it can also include PCI memory
164 holes).
166 We map EFI runtime services in the 'efi_pgd' PGD in a 64GB large virtual
167 memory window (this size is arbitrary, it can be raised later if needed).
168 The mappings are not part of any other kernel PGD and are only available
169 during EFI runtime calls.
171 Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
172 physical memory, vmalloc/ioremap space and virtual memory map are randomized.
173 Their order is preserved but their base will be offset early at boot time.
175 Be very careful vs. KASLR when changing anything here. The KASLR address
176 range must not overlap with anything except the KASAN shadow area, which is
177 correct as KASAN disables KASLR.
179 For both 4- and 5-level layouts, the STACKLEAK_POISON value in the last 2MB
180 hole: ffffffffffff4111