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SPDX-License-Identifier: GPL-2.02 3=====================================4Virtual Memory Layout on RISC-V Linux5=====================================6 7:Author: Alexandre Ghiti <alex@ghiti.fr>8:Date: 12 February 20219 10This document describes the virtual memory layout used by the RISC-V Linux11Kernel.12 13RISC-V Linux Kernel 32bit14=========================15 16RISC-V Linux Kernel SV3217------------------------18 19TODO20 21RISC-V Linux Kernel 64bit22=========================23 24The RISC-V privileged architecture document states that the 64bit addresses25"must have bits 63–48 all equal to bit 47, or else a page-fault exception will26occur.": that splits the virtual address space into 2 halves separated by a very27big hole, the lower half is where the userspace resides, the upper half is where28the RISC-V Linux Kernel resides.29 30RISC-V Linux Kernel SV3931------------------------32 33::34 35 ========================================================================================================================36 Start addr | Offset | End addr | Size | VM area description37 ========================================================================================================================38 | | | |39 0000000000000000 | 0 | 0000003fffffffff | 256 GB | user-space virtual memory, different per mm40 __________________|____________|__________________|_________|___________________________________________________________41 | | | |42 0000004000000000 | +256 GB | ffffffbfffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical43 | | | | virtual memory addresses up to the -256 GB44 | | | | 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 | fixmap51 ffffffc4ff000000 | -236 GB | ffffffc4ffffffff | 16 MB | PCI io52 ffffffc500000000 | -236 GB | ffffffc5ffffffff | 4 GB | vmemmap53 ffffffc600000000 | -232 GB | ffffffd5ffffffff | 64 GB | vmalloc/ioremap space54 ffffffd600000000 | -168 GB | fffffff5ffffffff | 128 GB | direct mapping of all physical memory55 | | | |56 fffffff700000000 | -36 GB | fffffffeffffffff | 32 GB | kasan57 __________________|____________|__________________|_________|____________________________________________________________58 |59 |60 ____________________________________________________________|____________________________________________________________61 | | | |62 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF63 ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel64 __________________|____________|__________________|_________|____________________________________________________________65 66 67RISC-V Linux Kernel SV4868------------------------69 70::71 72 ========================================================================================================================73 Start addr | Offset | End addr | Size | VM area description74 ========================================================================================================================75 | | | |76 0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm77 __________________|____________|__________________|_________|___________________________________________________________78 | | | |79 0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical80 | | | | virtual memory addresses up to the -128 TB81 | | | | 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 | fixmap88 ffff8d7fff000000 | -114.5 TB | ffff8d7fffffffff | 16 MB | PCI io89 ffff8d8000000000 | -114.5 TB | ffff8f7fffffffff | 2 TB | vmemmap90 ffff8f8000000000 | -112.5 TB | ffffaf7fffffffff | 32 TB | vmalloc/ioremap space91 ffffaf8000000000 | -80.5 TB | ffffef7fffffffff | 64 TB | direct mapping of all physical memory92 ffffef8000000000 | -16.5 TB | fffffffeffffffff | 16.5 TB | kasan93 __________________|____________|__________________|_________|____________________________________________________________94 |95 | Identical layout to the 39-bit one from here on:96 ____________________________________________________________|____________________________________________________________97 | | | |98 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF99 ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel100 __________________|____________|__________________|_________|____________________________________________________________101 102 103RISC-V Linux Kernel SV57104------------------------105 106::107 108 ========================================================================================================================109 Start addr | Offset | End addr | Size | VM area description110 ========================================================================================================================111 | | | |112 0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm113 __________________|____________|__________________|_________|___________________________________________________________114 | | | |115 0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, almost 64 bits wide hole of non-canonical116 | | | | virtual memory addresses up to the -64 PB117 | | | | 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 | fixmap124 ff1bffffff000000 | -57 PB | ff1bffffffffffff | 16 MB | PCI io125 ff1c000000000000 | -57 PB | ff1fffffffffffff | 1 PB | vmemmap126 ff20000000000000 | -56 PB | ff5fffffffffffff | 16 PB | vmalloc/ioremap space127 ff60000000000000 | -40 PB | ffdeffffffffffff | 32 PB | direct mapping of all physical memory128 ffdf000000000000 | -8 PB | fffffffeffffffff | 8 PB | kasan129 __________________|____________|__________________|_________|____________________________________________________________130 |131 | Identical layout to the 39-bit one from here on:132 ____________________________________________________________|____________________________________________________________133 | | | |134 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF135 ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel136 __________________|____________|__________________|_________|____________________________________________________________137