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[220.132.236.182]) by smtp.gmail.com with ESMTPSA id c188sm1500699pfb.151.2020.02.18.23.28.36 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 18 Feb 2020 23:28:37 -0800 (PST) From: Vincent Chen To: paul.walmsley@sifive.com, palmer@dabbelt.com Subject: [PATCH 0/2] solve static percpu symbol issue in module and refine code model of module Date: Wed, 19 Feb 2020 15:28:22 +0800 Message-Id: <1582097304-5547-1-git-send-email-vincent.chen@sifive.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200218_232842_372120_52A0BE90 X-CRM114-Status: GOOD ( 11.42 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.3 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:644 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Vincent Chen , linux-riscv@lists.infradead.org, deanbo422@gmail.com Sender: "linux-riscv" Errors-To: linux-riscv-bounces+patchwork-linux-riscv=patchwork.kernel.org@lists.infradead.org The compiler uses the PIC-relative method to access static variables instead of GOT when the code model is PIC. Therefore, the limitation of the access range from the instruction to the symbol address is +-2GB. Under this circumstance, the kernel cannot load a kernel module if this module has static per-CPU symbols declared by DEFINE_PER_CPU(). The reason is that kernel relocates the .data..percpu section of the kernel module to the end of kernel's .data..percpu. Hence, the distance between the per-CPU symbols and the instruction will exceed the 2GB limits. To solve this problem, the kernel should place the loaded module in the memory area [&_end-2G, VMALLOC_END]. Becuase the loaded module locates in the region [＆_end-2G，VMALLOC_END] at runtime, the distance from the module start to the end of the kernel image does not exceed 2GB. Hence, the second patch changes the code model of the kernel module from PIC to medany to improve the performance of data access. Vincent Chen (2): riscv: avoid the PIC offset of static percpu data in module beyond 2G limits riscv: Replace PIC with medany to improve data accessing in module arch/riscv/Makefile | 6 ++++-- arch/riscv/kernel/module.c | 18 ++++++++++++++++++ 2 files changed, 22 insertions(+), 2 deletions(-)