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 4A207C32792 for ; Tue, 23 Aug 2022 01:43:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238537AbiHWBnD (ORCPT ); Mon, 22 Aug 2022 21:43:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234840AbiHWBnB (ORCPT ); Mon, 22 Aug 2022 21:43:01 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7EBB15A80E for ; Mon, 22 Aug 2022 18:43:00 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MBX486msQznThm; Tue, 23 Aug 2022 09:40:40 +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; Tue, 23 Aug 2022 09:42:58 +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: Tue, 23 Aug 2022 09:42:57 +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: dggems705-chm.china.huawei.com (10.3.19.182) 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 2022/8/22 18:23, Muchun Song wrote: > > >> On Aug 22, 2022, at 16:45, Miaohe Lin wrote: >> >> On 2022/8/20 16:12, 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 found another place where is a similar case. See kasan_populate_vmalloc_pte() in >>> mm/kasan/shadow.c. >> >> Thanks for your report. >> >>> >>> Should we fix it as well? >> >> I'm not familiar with kasan yet, but I think memory barrier is needed here or memory corrupt >> can't be detected until the contents are visible. smp_mb__after_atomic before set_pte_at should >> be enough? What's your opinion? > > I didn’t see any atomic operation between set_pte_at() and memset(), I don’t think > smp_mb__after_atomic() is feasible if we really need to insert a barrier. I suggest Oh, it should be smp_mb__after_spinlock(), i.e. something like below: diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c index 0e3648b603a6..38e503c89740 100644 --- a/mm/kasan/shadow.c +++ b/mm/kasan/shadow.c @@ -277,6 +277,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr, spin_lock(&init_mm.page_table_lock); if (likely(pte_none(*ptep))) { + smp_mb__after_spinlock(); set_pte_at(&init_mm, addr, ptep, pte); page = 0; } Does this make sense for you? > you to send a RFC patch to KASAN maintainers, they are more familiar with this than > us. Sounds like a good idea. Will do it. Thanks, Miaohe Lin