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 BA4BEC25B08 for ; Wed, 17 Aug 2022 08:41:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235094AbiHQIlu (ORCPT ); Wed, 17 Aug 2022 04:41:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234851AbiHQIlr (ORCPT ); Wed, 17 Aug 2022 04:41:47 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 062737E811 for ; Wed, 17 Aug 2022 01:41:43 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4M71cr1ZgDz1N7Hc; Wed, 17 Aug 2022 16:38:20 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 17 Aug 2022 16:41:40 +0800 Subject: Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at() To: Muchun Song CC: Andrew Morton , Mike Kravetz , Muchun Song , Linux MM , References: <20220816130553.31406-1-linmiaohe@huawei.com> <20220816130553.31406-5-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: Date: Wed, 17 Aug 2022 16:41:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/17 10:53, Muchun Song wrote: > > >> On Aug 16, 2022, at 21:05, Miaohe Lin wrote: >> >> The memory barrier smp_wmb() is needed to make sure that preceding stores >> to the page contents become visible before the below set_pte_at() write. > > I’m not sure if you are right. I think it is set_pte_at()’s responsibility. Maybe not. There're many call sites do the similar things: hugetlb_mcopy_atomic_pte __do_huge_pmd_anonymous_page collapse_huge_page do_anonymous_page migrate_vma_insert_page mcopy_atomic_pte Take do_anonymous_page as an example: /* * The memory barrier inside __SetPageUptodate makes sure that * preceding stores to the page contents become visible before * the set_pte_at() write. */ __SetPageUptodate(page); So I think a memory barrier is needed before the set_pte_at() write. Or am I miss something? Thanks, Miaohe Lin > Take arm64 (since it is a Relaxed Memory Order model) as an example (the > following code snippet is set_pte()), I see a barrier guarantee. So I am > curious what issues you are facing. So I want to know the basis for you to > do this change. > > static inline void set_pte(pte_t *ptep, pte_t pte) > { > *ptep = pte; > > /* > * Only if the new pte is valid and kernel, otherwise TLB maintenance > * or update_mmu_cache() have the necessary barriers. > */ > if (pte_valid_not_user(pte)) { > dsb(ishst); > isb(); > } > } > > Thanks. >