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\xE2\x80\x9348 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 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 | | | | 61 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF 62 ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel 63 __________________|____________|__________________|_________|____________________________________________________________ 64