diff options
Diffstat (limited to 'Documentation/riscv')
| -rw-r--r-- | Documentation/riscv/boot-image-header.rst | 62 | ||||
| -rw-r--r-- | Documentation/riscv/features.rst | 3 | ||||
| -rw-r--r-- | Documentation/riscv/index.rst | 20 | ||||
| -rw-r--r-- | Documentation/riscv/patch-acceptance.rst | 35 | ||||
| -rw-r--r-- | Documentation/riscv/uabi.rst | 6 | ||||
| -rw-r--r-- | Documentation/riscv/vm-layout.rst | 99 |
6 files changed, 225 insertions, 0 deletions
diff --git a/Documentation/riscv/boot-image-header.rst b/Documentation/riscv/boot-image-header.rst new file mode 100644 index 000000000..d77525338 --- /dev/null +++ b/Documentation/riscv/boot-image-header.rst @@ -0,0 +1,62 @@ +================================= +Boot image header in RISC-V Linux +================================= + +:Author: Atish Patra <atish.patra@wdc.com> +:Date: 20 May 2019 + +This document only describes the boot image header details for RISC-V Linux. + +TODO: + Write a complete booting guide. + +The following 64-byte header is present in decompressed Linux kernel image:: + + u32 code0; /* Executable code */ + u32 code1; /* Executable code */ + u64 text_offset; /* Image load offset, little endian */ + u64 image_size; /* Effective Image size, little endian */ + u64 flags; /* kernel flags, little endian */ + u32 version; /* Version of this header */ + u32 res1 = 0; /* Reserved */ + u64 res2 = 0; /* Reserved */ + u64 magic = 0x5643534952; /* Magic number, little endian, "RISCV" */ + u32 magic2 = 0x05435352; /* Magic number 2, little endian, "RSC\x05" */ + u32 res3; /* Reserved for PE COFF offset */ + +This header format is compliant with PE/COFF header and largely inspired from +ARM64 header. Thus, both ARM64 & RISC-V header can be combined into one common +header in future. + +Notes +===== + +- This header can also be reused to support EFI stub for RISC-V in future. EFI + specification needs PE/COFF image header in the beginning of the kernel image + in order to load it as an EFI application. In order to support EFI stub, + code0 should be replaced with "MZ" magic string and res3(at offset 0x3c) should + point to the rest of the PE/COFF header. + +- version field indicate header version number + + ========== ============= + Bits 0:15 Minor version + Bits 16:31 Major version + ========== ============= + + This preserves compatibility across newer and older version of the header. + The current version is defined as 0.2. + +- The "magic" field is deprecated as of version 0.2. In a future + release, it may be removed. This originally should have matched up + with the ARM64 header "magic" field, but unfortunately does not. + The "magic2" field replaces it, matching up with the ARM64 header. + +- In current header, the flags field has only one field. + + ===== ==================================== + Bit 0 Kernel endianness. 1 if BE, 0 if LE. + ===== ==================================== + +- Image size is mandatory for boot loader to load kernel image. Booting will + fail otherwise. diff --git a/Documentation/riscv/features.rst b/Documentation/riscv/features.rst new file mode 100644 index 000000000..c70ef6ac2 --- /dev/null +++ b/Documentation/riscv/features.rst @@ -0,0 +1,3 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. kernel-feat:: $srctree/Documentation/features riscv diff --git a/Documentation/riscv/index.rst b/Documentation/riscv/index.rst new file mode 100644 index 000000000..2e5b18fbb --- /dev/null +++ b/Documentation/riscv/index.rst @@ -0,0 +1,20 @@ +=================== +RISC-V architecture +=================== + +.. toctree:: + :maxdepth: 1 + + boot-image-header + vm-layout + patch-acceptance + uabi + + features + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/riscv/patch-acceptance.rst b/Documentation/riscv/patch-acceptance.rst new file mode 100644 index 000000000..dfe0ac562 --- /dev/null +++ b/Documentation/riscv/patch-acceptance.rst @@ -0,0 +1,35 @@ +.. SPDX-License-Identifier: GPL-2.0 + +arch/riscv maintenance guidelines for developers +================================================ + +Overview +-------- +The RISC-V instruction set architecture is developed in the open: +in-progress drafts are available for all to review and to experiment +with implementations. New module or extension drafts can change +during the development process - sometimes in ways that are +incompatible with previous drafts. This flexibility can present a +challenge for RISC-V Linux maintenance. Linux maintainers disapprove +of churn, and the Linux development process prefers well-reviewed and +tested code over experimental code. We wish to extend these same +principles to the RISC-V-related code that will be accepted for +inclusion in the kernel. + +Submit Checklist Addendum +------------------------- +We'll only accept patches for new modules or extensions if the +specifications for those modules or extensions are listed as being +"Frozen" or "Ratified" by the RISC-V Foundation. (Developers may, of +course, maintain their own Linux kernel trees that contain code for +any draft extensions that they wish.) + +Additionally, the RISC-V specification allows implementors to create +their own custom extensions. These custom extensions aren't required +to go through any review or ratification process by the RISC-V +Foundation. To avoid the maintenance complexity and potential +performance impact of adding kernel code for implementor-specific +RISC-V extensions, we'll only to accept patches for extensions that +have been officially frozen or ratified by the RISC-V Foundation. +(Implementors, may, of course, maintain their own Linux kernel trees +containing code for any custom extensions that they wish.) diff --git a/Documentation/riscv/uabi.rst b/Documentation/riscv/uabi.rst new file mode 100644 index 000000000..21a82cfb6 --- /dev/null +++ b/Documentation/riscv/uabi.rst @@ -0,0 +1,6 @@ +.. SPDX-License-Identifier: GPL-2.0 + +RISC-V Linux User ABI +===================== + +Misaligned accesses are supported in userspace, but they may perform poorly. diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst new file mode 100644 index 000000000..edb533128 --- /dev/null +++ b/Documentation/riscv/vm-layout.rst @@ -0,0 +1,99 @@ +.. 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: + ____________________________________________________________|___________________________________________________________ + | | | | + ffffffc6fea00000 | -228 GB | ffffffc6feffffff | 6 MB | fixmap + 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 + __________________|____________|__________________|_________|____________________________________________________________ + | + | + ____________________________________________________________|____________________________________________________________ + | | | | + ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF + ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel + __________________|____________|__________________|_________|____________________________________________________________ + + +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: + ____________________________________________________________|___________________________________________________________ + | | | | + ffff8d7ffea00000 | -114.5 TB | ffff8d7ffeffffff | 6 MB | fixmap + 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 + __________________|____________|__________________|_________|____________________________________________________________ |