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 1FBC3C433FE for ; Fri, 21 Oct 2022 12:23:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229506AbiJUMXU (ORCPT ); Fri, 21 Oct 2022 08:23:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57948 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229484AbiJUMXS (ORCPT ); Fri, 21 Oct 2022 08:23:18 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5FF7476950 for ; Fri, 21 Oct 2022 05:23:16 -0700 (PDT) Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4Mv3Qq6Z18z15Lxs; Fri, 21 Oct 2022 20:18:27 +0800 (CST) Received: from kwepemm600017.china.huawei.com (7.193.23.234) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Fri, 21 Oct 2022 20:23:14 +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 15.1.2375.31; Fri, 21 Oct 2022 20:23:12 +0800 Message-ID: <09d1c410-5690-7158-8982-48ceec8ab64e@huawei.com> Date: Fri, 21 Oct 2022 20:23:12 +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: Palmer Dabbelt CC: , Paul Walmsley , , , , , , References: From: Tong Tiangen In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.234] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) 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 2022/9/22 4:25, Palmer Dabbelt 写道: > On Sat, 27 Aug 2022 03:39:38 PDT (-0700), tongtiangen@huawei.com wrote: >> >> >> 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. > > Generally we need some use of the code in the upstream kernel to justify > its existence.  In this case I don't really see that: it's just another > type that's exactly the same as the existing one, having some out of > tree code that depends on making these types do something different > isn't a sufficient justification. > . Hi palmer: I agree with this point very much，many thanks. Tong.