[PATCH v2 3/3] docs: riscv: Define behavior of mmap

From: Charlie Jenkins <charlie@rivosinc.com>
To: Alexandre Ghiti <alexghiti@rivosinc.com>,
	 Paul Walmsley <paul.walmsley@sifive.com>,
	 Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,  Shuah Khan <shuah@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,  Yangyu Chen <cyy@cyyself.name>
Cc: linux-mm@kvack.org, linux-riscv@lists.infradead.org,
	 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	 linux-doc@vger.kernel.org,
	Charlie Jenkins <charlie@rivosinc.com>
Subject: [PATCH v2 3/3] docs: riscv: Define behavior of mmap
Date: Tue, 30 Jan 2024 11:04:32 -0800	[thread overview]
Message-ID: <20240130-use_mmap_hint_address-v2-3-f34ebfd33053@rivosinc.com> (raw)
In-Reply-To: <20240130-use_mmap_hint_address-v2-0-f34ebfd33053@rivosinc.com>

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>
---
 Documentation/arch/riscv/vm-layout.rst | 16 +++++-----------
 1 file 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`.

-- 
2.43.0


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
