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Documentation: riscv: Add documentation that describes the VM layout This new document presents the RISC-V virtual memory layout and is based one the x86 one: it describes the different limits of the different regions of the virtual address space. Signed-off-by: Alexandre Ghiti <alex@ghiti.fr> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2021-04-11 16:41:45 +00:00
.. 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:
____________________________________________________________|___________________________________________________________
| | | |
riscv: Move early dtb mapping into the fixmap region riscv establishes 2 virtual mappings: - early_pg_dir maps the kernel which allows to discover the system memory - swapper_pg_dir installs the final mapping (linear mapping included) We used to map the dtb in early_pg_dir using DTB_EARLY_BASE_VA, and this mapping was not carried over in swapper_pg_dir. It happens that early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is setup otherwise we could allocate reserved memory defined in the dtb. And this function initializes reserved_mem variable with addresses that lie in the early_pg_dir dtb mapping: when those addresses are reused with swapper_pg_dir, this mapping does not exist and then we trap. The previous "fix" was incorrect as early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is set up otherwise we could allocate in reserved memory defined in the dtb. So move the dtb mapping in the fixmap region which is established in early_pg_dir and handed over to swapper_pg_dir. Fixes: 922b0375fc93 ("riscv: Fix memblock reservation for device tree blob") Fixes: 8f3a2b4a96dc ("RISC-V: Move DT mapping outof fixmap") Fixes: 50e63dd8ed92 ("riscv: fix reserved memory setup") Reported-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/all/f8e67f82-103d-156c-deb0-d6d6e2756f5e@microchip.com/ Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Tested-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/r/20230329081932.79831-2-alexghiti@rivosinc.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-03-29 08:19:30 +00:00
ffffffc6fea00000 | -228 GB | ffffffc6feffffff | 6 MB | fixmap
riscv: Move KASAN mapping next to the kernel mapping 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>
2021-12-06 10:46:45 +00:00
ffffffc6ff000000 | -228 GB | ffffffc6ffffffff | 16 MB | PCI io
ffffffc700000000 | -228 GB | ffffffc7ffffffff | 4 GB | vmemmap
ffffffc800000000 | -224 GB | ffffffd7ffffffff | 64 GB | vmalloc/ioremap space
ffffffd800000000 | -160 GB | fffffff6ffffffff | 124 GB | direct mapping of all physical memory
fffffff700000000 | -36 GB | fffffffeffffffff | 32 GB | kasan
Documentation: riscv: Add documentation that describes the VM layout This new document presents the RISC-V virtual memory layout and is based one the x86 one: it describes the different limits of the different regions of the virtual address space. Signed-off-by: Alexandre Ghiti <alex@ghiti.fr> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2021-04-11 16:41:45 +00:00
__________________|____________|__________________|_________|____________________________________________________________
|
|
____________________________________________________________|____________________________________________________________
| | | |
riscv: Ensure BPF_JIT_REGION_START aligned with PMD size Andreas reported commit fc8504765ec5 ("riscv: bpf: Avoid breaking W^X") breaks booting with one kind of defconfig, I reproduced a kernel panic with the defconfig: [ 0.138553] Unable to handle kernel paging request at virtual address ffffffff81201220 [ 0.139159] Oops [#1] [ 0.139303] Modules linked in: [ 0.139601] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc5-default+ #1 [ 0.139934] Hardware name: riscv-virtio,qemu (DT) [ 0.140193] epc : __memset+0xc4/0xfc [ 0.140416] ra : skb_flow_dissector_init+0x1e/0x82 [ 0.140609] epc : ffffffff8029806c ra : ffffffff8033be78 sp : ffffffe001647da0 [ 0.140878] gp : ffffffff81134b08 tp : ffffffe001654380 t0 : ffffffff81201158 [ 0.141156] t1 : 0000000000000002 t2 : 0000000000000154 s0 : ffffffe001647dd0 [ 0.141424] s1 : ffffffff80a43250 a0 : ffffffff81201220 a1 : 0000000000000000 [ 0.141654] a2 : 000000000000003c a3 : ffffffff81201258 a4 : 0000000000000064 [ 0.141893] a5 : ffffffff8029806c a6 : 0000000000000040 a7 : ffffffffffffffff [ 0.142126] s2 : ffffffff81201220 s3 : 0000000000000009 s4 : ffffffff81135088 [ 0.142353] s5 : ffffffff81135038 s6 : ffffffff8080ce80 s7 : ffffffff80800438 [ 0.142584] s8 : ffffffff80bc6578 s9 : 0000000000000008 s10: ffffffff806000ac [ 0.142810] s11: 0000000000000000 t3 : fffffffffffffffc t4 : 0000000000000000 [ 0.143042] t5 : 0000000000000155 t6 : 00000000000003ff [ 0.143220] status: 0000000000000120 badaddr: ffffffff81201220 cause: 000000000000000f [ 0.143560] [<ffffffff8029806c>] __memset+0xc4/0xfc [ 0.143859] [<ffffffff8061e984>] init_default_flow_dissectors+0x22/0x60 [ 0.144092] [<ffffffff800010fc>] do_one_initcall+0x3e/0x168 [ 0.144278] [<ffffffff80600df0>] kernel_init_freeable+0x1c8/0x224 [ 0.144479] [<ffffffff804868a8>] kernel_init+0x12/0x110 [ 0.144658] [<ffffffff800022de>] ret_from_exception+0x0/0xc [ 0.145124] ---[ end trace f1e9643daa46d591 ]--- After some investigation, I think I found the root cause: commit 2bfc6cd81bd ("move kernel mapping outside of linear mapping") moves BPF JIT region after the kernel: | #define BPF_JIT_REGION_START PFN_ALIGN((unsigned long)&_end) The &_end is unlikely aligned with PMD size, so the front bpf jit region sits with part of kernel .data section in one PMD size mapping. But kernel is mapped in PMD SIZE, when bpf_jit_binary_lock_ro() is called to make the first bpf jit prog ROX, we will make part of kernel .data section RO too, so when we write to, for example memset the .data section, MMU will trigger a store page fault. To fix the issue, we need to ensure the BPF JIT region is PMD size aligned. This patch acchieve this goal by restoring the BPF JIT region to original position, I.E the 128MB before kernel .text section. The modification to kasan_init.c is inspired by Alexandre. Fixes: fc8504765ec5 ("riscv: bpf: Avoid breaking W^X") Reported-by: Andreas Schwab <schwab@linux-m68k.org> Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2021-06-18 14:09:13 +00:00
ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF
ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel
Documentation: riscv: Add documentation that describes the VM layout This new document presents the RISC-V virtual memory layout and is based one the x86 one: it describes the different limits of the different regions of the virtual address space. Signed-off-by: Alexandre Ghiti <alex@ghiti.fr> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2021-04-11 16:41:45 +00:00
__________________|____________|__________________|_________|____________________________________________________________
Documentation: riscv: Add sv48 description to VM layout sv48 was just introduced, so add its virtual memory layout to the documentation. Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2021-12-06 10:46:55 +00:00
RISC-V Linux Kernel SV48
------------------------
::
========================================================================================================================
Start addr | Offset | End addr | Size | VM area description
========================================================================================================================
| | | |
0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm
__________________|____________|__________________|_________|___________________________________________________________
| | | |
0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
| | | | virtual memory addresses up to the -128 TB
| | | | starting offset of kernel mappings.
__________________|____________|__________________|_________|___________________________________________________________
|
| Kernel-space virtual memory, shared between all processes:
____________________________________________________________|___________________________________________________________
| | | |
riscv: Move early dtb mapping into the fixmap region riscv establishes 2 virtual mappings: - early_pg_dir maps the kernel which allows to discover the system memory - swapper_pg_dir installs the final mapping (linear mapping included) We used to map the dtb in early_pg_dir using DTB_EARLY_BASE_VA, and this mapping was not carried over in swapper_pg_dir. It happens that early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is setup otherwise we could allocate reserved memory defined in the dtb. And this function initializes reserved_mem variable with addresses that lie in the early_pg_dir dtb mapping: when those addresses are reused with swapper_pg_dir, this mapping does not exist and then we trap. The previous "fix" was incorrect as early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is set up otherwise we could allocate in reserved memory defined in the dtb. So move the dtb mapping in the fixmap region which is established in early_pg_dir and handed over to swapper_pg_dir. Fixes: 922b0375fc93 ("riscv: Fix memblock reservation for device tree blob") Fixes: 8f3a2b4a96dc ("RISC-V: Move DT mapping outof fixmap") Fixes: 50e63dd8ed92 ("riscv: fix reserved memory setup") Reported-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/all/f8e67f82-103d-156c-deb0-d6d6e2756f5e@microchip.com/ Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Tested-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/r/20230329081932.79831-2-alexghiti@rivosinc.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-03-29 08:19:30 +00:00
ffff8d7ffea00000 | -114.5 TB | ffff8d7ffeffffff | 6 MB | fixmap
Documentation: riscv: Add sv48 description to VM layout sv48 was just introduced, so add its virtual memory layout to the documentation. Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2021-12-06 10:46:55 +00:00
ffff8d7fff000000 | -114.5 TB | ffff8d7fffffffff | 16 MB | PCI io
ffff8d8000000000 | -114.5 TB | ffff8f7fffffffff | 2 TB | vmemmap
ffff8f8000000000 | -112.5 TB | ffffaf7fffffffff | 32 TB | vmalloc/ioremap space
ffffaf8000000000 | -80.5 TB | ffffef7fffffffff | 64 TB | direct mapping of all physical memory
ffffef8000000000 | -16.5 TB | fffffffeffffffff | 16.5 TB | kasan
__________________|____________|__________________|_________|____________________________________________________________
|
| Identical layout to the 39-bit one from here on:
____________________________________________________________|____________________________________________________________
| | | |
ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF
ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel
__________________|____________|__________________|_________|____________________________________________________________
Documentation: riscv: Document the sv57 VM layout RISC-V has been supporting the "sv57" address translation mode for a while, but is has not been added to the VM layout documentation. Let us fix that. Signed-off-by: Björn Töpel <bjorn@rivosinc.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20221118171556.1612190-1-bjorn@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-11-18 17:15:56 +00:00
RISC-V Linux Kernel SV57
------------------------
::
========================================================================================================================
Start addr | Offset | End addr | Size | VM area description
========================================================================================================================
| | | |
0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm
__________________|____________|__________________|_________|___________________________________________________________
| | | |
0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, almost 64 bits wide hole of non-canonical
| | | | virtual memory addresses up to the -64 PB
| | | | starting offset of kernel mappings.
__________________|____________|__________________|_________|___________________________________________________________
|
| Kernel-space virtual memory, shared between all processes:
____________________________________________________________|___________________________________________________________
| | | |
riscv: Move early dtb mapping into the fixmap region riscv establishes 2 virtual mappings: - early_pg_dir maps the kernel which allows to discover the system memory - swapper_pg_dir installs the final mapping (linear mapping included) We used to map the dtb in early_pg_dir using DTB_EARLY_BASE_VA, and this mapping was not carried over in swapper_pg_dir. It happens that early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is setup otherwise we could allocate reserved memory defined in the dtb. And this function initializes reserved_mem variable with addresses that lie in the early_pg_dir dtb mapping: when those addresses are reused with swapper_pg_dir, this mapping does not exist and then we trap. The previous "fix" was incorrect as early_init_fdt_scan_reserved_mem() must be called before swapper_pg_dir is set up otherwise we could allocate in reserved memory defined in the dtb. So move the dtb mapping in the fixmap region which is established in early_pg_dir and handed over to swapper_pg_dir. Fixes: 922b0375fc93 ("riscv: Fix memblock reservation for device tree blob") Fixes: 8f3a2b4a96dc ("RISC-V: Move DT mapping outof fixmap") Fixes: 50e63dd8ed92 ("riscv: fix reserved memory setup") Reported-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/all/f8e67f82-103d-156c-deb0-d6d6e2756f5e@microchip.com/ Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Tested-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/r/20230329081932.79831-2-alexghiti@rivosinc.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-03-29 08:19:30 +00:00
ff1bfffffea00000 | -57 PB | ff1bfffffeffffff | 6 MB | fixmap
Documentation: riscv: Document the sv57 VM layout RISC-V has been supporting the "sv57" address translation mode for a while, but is has not been added to the VM layout documentation. Let us fix that. Signed-off-by: Björn Töpel <bjorn@rivosinc.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20221118171556.1612190-1-bjorn@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-11-18 17:15:56 +00:00
ff1bffffff000000 | -57 PB | ff1bffffffffffff | 16 MB | PCI io
ff1c000000000000 | -57 PB | ff1fffffffffffff | 1 PB | vmemmap
ff20000000000000 | -56 PB | ff5fffffffffffff | 16 PB | vmalloc/ioremap space
ff60000000000000 | -40 PB | ffdeffffffffffff | 32 PB | direct mapping of all physical memory
ffdf000000000000 | -8 PB | fffffffeffffffff | 8 PB | kasan
__________________|____________|__________________|_________|____________________________________________________________
|
| Identical layout to the 39-bit one from here on:
____________________________________________________________|____________________________________________________________
| | | |
ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF
ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel
__________________|____________|__________________|_________|____________________________________________________________
RISC-V: mm: Document mmap changes The behavior of mmap is modified with this patch series, so explain the changes to the mmap hint address behavior. Signed-off-by: Charlie Jenkins <charlie@rivosinc.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20230809232218.849726-5-charlie@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-08-09 23:22:04 +00:00
Userspace VAs
--------------------
To maintain compatibility with software that relies on the VA space with a
maximum of 48 bits the kernel will, by default, return virtual addresses to
userspace from a 48-bit range (sv48). This default behavior is achieved by
passing 0 into the hint address parameter of mmap. On CPUs with an address space
smaller than sv48, the CPU maximum supported address space will be the default.
Software can "opt-in" to receiving VAs from another VA space by providing
docs: riscv: Define behavior of mmap Define mmap on riscv to not provide an address that uses more bits than the hint address, if provided. Signed-off-by: Charlie Jenkins <charlie@rivosinc.com> Link: https://lore.kernel.org/r/20240130-use_mmap_hint_address-v3-3-8a655cfa8bcb@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2024-01-31 01:07:02 +00:00
a hint address to mmap. When a hint address is passed to mmap, the returned
address will never use more bits than the hint address. For example, if a hint
address of `1 << 40` is passed to mmap, a valid returned address will never use
bits 41 through 63. If no mappable addresses are available in that range, mmap
will return `MAP_FAILED`.