| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ===================================== |
| Virtual Memory Layout on RISC-V Linux |
| ===================================== |
| |
| :Author: Alexandre Ghiti <alex@ghiti.fr> |
| :Date: 12 February 2021 |
| |
| This document describes the virtual memory layout used by the RISC-V Linux |
| Kernel. |
| |
| RISC-V Linux Kernel 32bit |
| ========================= |
| |
| RISC-V Linux Kernel SV32 |
| ------------------------ |
| |
| TODO |
| |
| RISC-V Linux Kernel 64bit |
| ========================= |
| |
| The RISC-V privileged architecture document states that the 64bit addresses |
| "must have bits 63–48 all equal to bit 47, or else a page-fault exception will |
| occur.": that splits the virtual address space into 2 halves separated by a very |
| big hole, the lower half is where the userspace resides, the upper half is where |
| the RISC-V Linux Kernel resides. |
| |
| RISC-V Linux Kernel SV39 |
| ------------------------ |
| |
| :: |
| |
| ======================================================================================================================== |
| Start addr | Offset | End addr | Size | VM area description |
| ======================================================================================================================== |
| | | | | |
| 0000000000000000 | 0 | 0000003fffffffff | 256 GB | user-space virtual memory, different per mm |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | | | | |
| 0000004000000000 | +256 GB | ffffffbfffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical |
| | | | | virtual memory addresses up to the -256 GB |
| | | | | starting offset of kernel mappings. |
| __________________|____________|__________________|_________|___________________________________________________________ |
| | |
| | Kernel-space virtual memory, shared between all processes: |
| ____________________________________________________________|___________________________________________________________ |
| | | | | |
| ffffffc000000000 | -256 GB | ffffffc7ffffffff | 32 GB | kasan |
| ffffffcefee00000 | -196 GB | ffffffcefeffffff | 2 MB | fixmap |
| ffffffceff000000 | -196 GB | ffffffceffffffff | 16 MB | PCI io |
| ffffffcf00000000 | -196 GB | ffffffcfffffffff | 4 GB | vmemmap |
| ffffffd000000000 | -192 GB | ffffffdfffffffff | 64 GB | vmalloc/ioremap space |
| ffffffe000000000 | -128 GB | ffffffff7fffffff | 124 GB | direct mapping of all physical memory |
| __________________|____________|__________________|_________|____________________________________________________________ |
| | |
| | |
| ____________________________________________________________|____________________________________________________________ |
| | | | | |
| ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF |
| ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel |
| __________________|____________|__________________|_________|____________________________________________________________ |
