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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 __________________|____________|__________________|_________|____________________________________________________________ 137