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Now that KASAN_SHADOW_OFFSET is defined at compile time as a config, this value must remain constant whatever the size of the virtual address space, which is only possible by pushing this region at the end of the address space next to the kernel mapping. Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
64 lines
3.5 KiB
ReStructuredText
64 lines
3.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=====================================
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Virtual Memory Layout on RISC-V Linux
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=====================================
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:Author: Alexandre Ghiti <alex@ghiti.fr>
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:Date: 12 February 2021
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This document describes the virtual memory layout used by the RISC-V Linux
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Kernel.
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RISC-V Linux Kernel 32bit
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=========================
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RISC-V Linux Kernel SV32
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------------------------
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TODO
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RISC-V Linux Kernel 64bit
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=========================
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The RISC-V privileged architecture document states that the 64bit addresses
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"must have bits 63–48 all equal to bit 47, or else a page-fault exception will
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occur.": that splits the virtual address space into 2 halves separated by a very
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big hole, the lower half is where the userspace resides, the upper half is where
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the RISC-V Linux Kernel resides.
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RISC-V Linux Kernel SV39
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------------------------
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::
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========================================================================================================================
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Start addr | Offset | End addr | Size | VM area description
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========================================================================================================================
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0000000000000000 | 0 | 0000003fffffffff | 256 GB | user-space virtual memory, different per mm
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__________________|____________|__________________|_________|___________________________________________________________
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| | | |
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0000004000000000 | +256 GB | ffffffbfffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -256 GB
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| | | | starting offset of kernel mappings.
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__________________|____________|__________________|_________|___________________________________________________________
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| Kernel-space virtual memory, shared between all processes:
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____________________________________________________________|___________________________________________________________
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| | | |
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ffffffc6fee00000 | -228 GB | ffffffc6feffffff | 2 MB | fixmap
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ffffffc6ff000000 | -228 GB | ffffffc6ffffffff | 16 MB | PCI io
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ffffffc700000000 | -228 GB | ffffffc7ffffffff | 4 GB | vmemmap
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ffffffc800000000 | -224 GB | ffffffd7ffffffff | 64 GB | vmalloc/ioremap space
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ffffffd800000000 | -160 GB | fffffff6ffffffff | 124 GB | direct mapping of all physical memory
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fffffff700000000 | -36 GB | fffffffeffffffff | 32 GB | kasan
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__________________|____________|__________________|_________|____________________________________________________________
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____________________________________________________________|____________________________________________________________
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ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF
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ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel
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__________________|____________|__________________|_________|____________________________________________________________
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