diff options
| author | Charlie Jenkins <charlie@rivosinc.com> | 2024-01-30 17:07:02 -0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-03-14 08:46:15 -0700 |
| commit | 371a3c2055dbb8a88754902fe19aa4fcc4318c29 (patch) | |
| tree | fd7e2fd1aaea26adf8513305998a38da95eceec8 /Documentation/arch | |
| parent | 73d05262a2ca28c72c5aec57d79b47c251fe77c5 (diff) | |
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>
Diffstat (limited to 'Documentation/arch')
| -rw-r--r-- | Documentation/arch/riscv/vm-layout.rst | 16 |
1 files changed, 5 insertions, 11 deletions
diff --git a/Documentation/arch/riscv/vm-layout.rst b/Documentation/arch/riscv/vm-layout.rst index 69ff6da1dbf8..e476b4386bd9 100644 --- a/Documentation/arch/riscv/vm-layout.rst +++ b/Documentation/arch/riscv/vm-layout.rst @@ -144,14 +144,8 @@ 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. +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`. |