| Message ID | 20230726164620.717288-5-charlie@rivosinc.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | RISC-V: mm: Make SV48 the default address space | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/cover_letter | success | Series has a cover letter |
| conchuod/tree_selection | success | Guessed tree name to be for-next at HEAD 471aba2e4760 |
| conchuod/fixes_present | success | Fixes tag not required for -next series |
| conchuod/maintainers_pattern | success | MAINTAINERS pattern errors before the patch: 4 and now 4 |
| conchuod/verify_signedoff | success | Signed-off-by tag matches author and committer |
| conchuod/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/build_rv64_clang_allmodconfig | success | Errors and warnings before: 9 this patch: 9 |
| conchuod/module_param | success | Was 0 now: 0 |
| conchuod/build_rv64_gcc_allmodconfig | success | Errors and warnings before: 9 this patch: 9 |
| conchuod/build_rv32_defconfig | fail | Build failed |
| conchuod/dtb_warn_rv64 | success | Errors and warnings before: 3 this patch: 3 |
| conchuod/header_inline | success | No static functions without inline keyword in header files |
| conchuod/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 25 lines checked |
| conchuod/build_rv64_nommu_k210_defconfig | success | Build OK |
| conchuod/verify_fixes | success | No Fixes tag |
| conchuod/build_rv64_nommu_virt_defconfig | success | Build OK |
diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst index 5462c84f4723..69ff6da1dbf8 100644 --- a/Documentation/riscv/vm-layout.rst +++ b/Documentation/riscv/vm-layout.rst @@ -133,3 +133,25 @@ RISC-V Linux Kernel SV57 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|____________________________________________________________ + + +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 +a hint address to mmap. A hint address passed to mmap will cause the largest +address space that fits entirely into the hint to be used, unless there is no +space left in the address space. If there is no space available in the requested +address space, an address in the next smallest available address space will be +returned. + +For example, in order to obtain 48-bit VA space, a hint address greater than +:code:`1 << 47` must be provided. Note that this is 47 due to sv48 userspace +ending at :code:`1 << 47` and the addresses beyond this are reserved for the +kernel. Similarly, to obtain 57-bit VA space addresses, a hint address greater +than or equal to :code:`1 << 56` must be provided.
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> --- Documentation/riscv/vm-layout.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)