From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74DB3C43218 for ; Tue, 11 Jun 2019 10:32:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 543D620665 for ; Tue, 11 Jun 2019 10:32:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387704AbfFKKcm (ORCPT ); Tue, 11 Jun 2019 06:32:42 -0400 Received: from foss.arm.com ([217.140.110.172]:58278 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387423AbfFKKcm (ORCPT ); Tue, 11 Jun 2019 06:32:42 -0400 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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