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[217.140.110.172]) by mx.google.com with ESMTP id h21si7975784ejj.356.2019.06.11.03.32.42 for ; Tue, 11 Jun 2019 03:32:42 -0700 (PDT) Received-SPF: pass (google.com: domain of vladimir.murzin@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vladimir.murzin@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=vladimir.murzin@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6D599337; Tue, 11 Jun 2019 03:32:41 -0700 (PDT) Received: from [10.1.29.141] (e121487-lin.cambridge.arm.com [10.1.29.141]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 21DD73F557; Tue, 11 Jun 2019 03:34:21 -0700 (PDT) Subject: Re: [PATCH 17/17] riscv: add nommu support To: Christoph Hellwig , Palmer Dabbelt Cc: Damien Le Moal , linux-riscv@lists.infradead.org, uclinux-dev@uclinux.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190610221621.10938-1-hch@lst.de> <20190610221621.10938-18-hch@lst.de> From: Vladimir Murzin Message-ID: Date: Tue, 11 Jun 2019 11:32:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190610221621.10938-18-hch@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/10/19 11:16 PM, Christoph Hellwig wrote: > Most of the patch is just stubbing out code not needed without page > tables, but there is an interesting detail in the signals implementation: > > - The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO > entry point, but the ELF VDSO is not supported for nommu Linux. > We instead copy the code to call the syscall onto the stack. On ARM we perform I/D cache synchronization after stack manipulation. OTOH, ARM port of uClibc provides SA_RESTORER with intention to avoid manipulation with stack and cache maintenance operations (yet kernel still performs such manipulation, IIUC, for backward compatibility) Cheers Vladimir