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Thu, 27 Jul 2023 14:26:56 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id c5-20020aa78c05000000b00682562b1549sm1912312pfd.24.2023.07.27.14.26.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jul 2023 14:26:56 -0700 (PDT) From: Charlie Jenkins To: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Cc: charlie@rivosinc.com, conor@kernel.org, paul.walmsley@sifive.com, palmer@rivosinc.com, aou@eecs.berkeley.edu, anup@brainfault.org, konstantin@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mick@ics.forth.gr, jrtc27@jrtc27.com, rdunlap@infradead.org, alexghiti@rivosinc.com Subject: [PATCH v8 4/4] RISC-V: mm: Document mmap changes Date: Thu, 27 Jul 2023 14:26:29 -0700 Message-ID: <20230727212647.4182407-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230727212647.4182407-1-charlie@rivosinc.com> References: <20230727212647.4182407-1-charlie@rivosinc.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 89047180016 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 35f5oehzaaf1pqdw9r9csmt5uaw99ffo X-HE-Tag: 1690493217-192763 X-HE-Meta: U2FsdGVkX19L8AhrT7Zlpf9pfC2X9giPxRcgp9V52A8/SKNPwpFY2YVTtCvAf/eLSVIQRc/dEYGf8S2JggKq57qHjQxDbcZvUVLhALmcSrG6qv/HUk8v3pvX/a1kNX4KOyANqQ0q4tFVmjjXeMjLtLPCDbsgwPQQbSHEFilUvh0B/Ab4/+XvWl8i5OAfN2izJECqkKcifH9vOEImuNMF4fXXVrXo4rO0n7HQH9UGLy1XwVGO82jM5AleAxywvJkuMxlW96gF36FqBbWaXwSLvuoc8fPjAxLzFiFYwQhJ+iJy7BTnmXwEg1TFvy4RXGxOkMOPpnfwQ8+UPwu6DI1SDV3Z87MfLZ5BH6EB1P5ueFxBVwbZXFLls5lrozLCy2bk+rLW2if+uR5fakR712pUZ6RO4gcci2gH0ozhKGjczK4YBl8w4Tq1Z7nOWjMDyrZTHgTRWk+8DYELLuiA007w8IareCncTw1edt8XPO1LE5BX00mmqbWcv+iKaB6qsU6HeX9VWpcCat2iKvELvNRCbEIk13qmTiIgqi3mNPwHtbpwAHcajWA7YvKzocO9sg67B9WgqcyyaChRFJ03YrJqE32AjHQtJG8uAMIwM/HeA7+aByp06W6RkOxEs0Q13njHtgNkR/vFsAerisjfhI/aDz7Tz7f0WgvxLHywGaYHMoOYS9AWOV9v+iOl5Psr/IcDJgPOhHQGi2k4RN9vGmYC8YXJ3zjdqlKjGeOS5+7o5RHETj20G71jBYWQqe1ePOhB3NMEk+5IjO+Caj6UYUNawz6v0KMiPMUjEdxOEQTDkiS8a2SWLR/8y6Ub1gH2iPxfWJx6mSFPkMVb0eX/x9jKoPrjrXeYdbaANyquXo0Vq6kgy4vX7ykvcTcqQnDyHONSJAI09FY7Yusuu18vf8srq8+Px93NfXRTPrL7T9rYByEUTKXHg14WbnA8oOWZTX4K87eOt1q6ciVb4w9Ap+3 lPn8pjF1 2Z7TzSa0DI+M55BIH4B3n6PCz+JmB1bIGbfhvtdyhkOGHYUB4YSQx3kEmyPFr//t726EbG8xLCGob2ywPCJHW9/zPzekoangDyfScQDmfIcdbVho881lh1LkuoMnuTW+o8n0B1TNLR9imBdSmxeueXEbk8/8KBxTDsiFTUPqHs0iim9pWZsW93kpeGKLcBDjp+tlT2PV05/9lMGySclwWi+bc8xsWiABB5RpecxWGYrX8IcJ3J3fWZp1efaVjJPFMTh5bEFT0Cp84nQFB+D8lweu7MmISNNZlTpgOdD3kWF18Nq/BduHJLKhqJfXxvcuqztycfntHuB1GKjvvZQ91KylQNZQtiYHnkPcR8hFJoJ8l6LXzSPiBIc5BPY6LN+MrexmK7LGFfgkvxbdM0sZAEdzooSB8N+PuU/SQrzPz8M7NYTLiWbetPvAm+DKhbFTk4Kcp X-Bogosity: Ham, tests=bogofilter, spamicity=0.007638, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 Reviewed-by: Alexandre Ghiti --- Documentation/riscv/vm-layout.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) 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.