| Alexandre Ghiti | 2a433cf | 2021-04-11 12:41:45 -0400 | [diff] [blame] | 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 | ffffffc000000000 | -256 GB | ffffffc7ffffffff | 32 GB | kasan |
| 51 | ffffffcefee00000 | -196 GB | ffffffcefeffffff | 2 MB | fixmap |
| 52 | ffffffceff000000 | -196 GB | ffffffceffffffff | 16 MB | PCI io |
| 53 | ffffffcf00000000 | -196 GB | ffffffcfffffffff | 4 GB | vmemmap |
| 54 | ffffffd000000000 | -192 GB | ffffffdfffffffff | 64 GB | vmalloc/ioremap space |
| 55 | ffffffe000000000 | -128 GB | ffffffff7fffffff | 124 GB | direct mapping of all physical memory |
| 56 | __________________|____________|__________________|_________|____________________________________________________________ |
| 57 | | |
| 58 | | |
| 59 | ____________________________________________________________|____________________________________________________________ |
| 60 | | | | | |
| Jisheng Zhang | 3a02764 | 2021-06-18 22:09:13 +0800 | [diff] [blame] | 61 | ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF |
| 62 | ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel |
| Alexandre Ghiti | 2a433cf | 2021-04-11 12:41:45 -0400 | [diff] [blame] | 63 | __________________|____________|__________________|_________|____________________________________________________________ |