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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A4ABECAAD2 for ; Sat, 27 Aug 2022 10:39:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231890AbiH0Kjq (ORCPT ); Sat, 27 Aug 2022 06:39:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229737AbiH0Kjn (ORCPT ); Sat, 27 Aug 2022 06:39:43 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ACA506C754 for ; Sat, 27 Aug 2022 03:39:42 -0700 (PDT) Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MFCnV21PgznTWK; Sat, 27 Aug 2022 18:37:18 +0800 (CST) Received: from kwepemm600017.china.huawei.com (7.193.23.234) by dggemv703-chm.china.huawei.com (10.3.19.46) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sat, 27 Aug 2022 18:39:40 +0800 Received: from [10.174.179.234] (10.174.179.234) by kwepemm600017.china.huawei.com (7.193.23.234) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sat, 27 Aug 2022 18:39:39 +0800 Message-ID: <301cd27e-d003-584b-2eb0-8fa025348cff@huawei.com> Date: Sat, 27 Aug 2022 18:39:38 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH -next v2 2/2] riscv: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support To: Andrew Jones CC: Paul Walmsley , Palmer Dabbelt , Palmer Dabbelt , Albert Ou , , , , , Guohanjun References: <20220815032025.2685516-1-tongtiangen@huawei.com> <20220815032025.2685516-3-tongtiangen@huawei.com> <20220825110602.bog5mjpascvikwxx@kamzik> <7718a9bc-e976-daeb-f490-e7b5190e50b6@huawei.com> <20220826081607.ci42sbffrmsfhk2w@kamzik> From: Tong Tiangen In-Reply-To: <20220826081607.ci42sbffrmsfhk2w@kamzik> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.234] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemm600017.china.huawei.com (7.193.23.234) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/8/26 16:16, Andrew Jones 写道: > On Fri, Aug 26, 2022 at 02:44:48PM +0800, Tong Tiangen wrote: >> >> >> 在 2022/8/25 19:06, Andrew Jones 写道: >>> On Mon, Aug 15, 2022 at 03:20:25AM +0000, Tong Tiangen wrote: >>>> Currently, The extable type EX_TYPE_UACCESS_ERR_ZERO is used by >>>> __get/put_kernel_nofault(), but those helpers are not uaccess type, so we >>>> add a new extable type EX_TYPE_KACCESS_ERR_ZERO which can be used by >>>> __get/put_kernel_no_fault(). >>>> >>>> Only refactor code without any functional changes. >>> >>> This isn't quite true. __get/put_kernel_nofault now sets a different >>> extable type (as the commit message says). But, nothing special seems >>> to be done with that, so there's effectively no functional change. Can >>> you please elaborate on the motivation for this change? Where will the >>> KACCESS type need to be distinguished from the UACCESS type? >> >> The introduction of EX_TYPE_KACCESS_ERR_ZERO does not change any function, >> but makes a correct distinction in the actual type, indicating that there >> are indeed some kaccess entries in extable. I think this optimization is >> more clear and reasonable. > > Well, creating new types, just for new type sake, just bloats code. > >> >> A few weeks ago, I did something similar on arm64[1]. I think this >> optimization can also be used on riscv. >> >> We can do some features that are used on uaccss but not applicable on >> kaccess in the future[2]. >> >> [1] >> https://lore.kernel.org/lkml/20220621072638.1273594-2-tongtiangen@huawei.com/ >> [2]https://lore.kernel.org/lkml/20220812070557.1028499-4-tongtiangen@huawei.com/ >> > > This is part of the information, but I had already found this. What's > still missing to me are the riscv patches, or at least a riscv plan, for > actually implementing something which requires kaccess and uaccess to have > distinct types. > > Thanks, > drew At present, there is no such plan on riscv, because it is rely on hardware support. I think this patch can be merged as a small code optimization and without any function change. Thanks, Tong. > > .