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 198D0EB64DD for ; Mon, 17 Jul 2023 02:33:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230348AbjGQCdk (ORCPT ); Sun, 16 Jul 2023 22:33:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230440AbjGQCdg (ORCPT ); Sun, 16 Jul 2023 22:33:36 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C623E71 for ; Sun, 16 Jul 2023 19:33:17 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4R45ff19TzzLnm8; Mon, 17 Jul 2023 10:30:50 +0800 (CST) Received: from [10.174.151.185] (10.174.151.185) 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 15.1.2507.27; Mon, 17 Jul 2023 10:33:14 +0800 Subject: Re: [PATCH 1/4] mm/swapfile: fix wrong swap entry type for hwpoisoned swapcache page To: Matthew Wilcox CC: , , , , References: <20230715031729.2420338-1-linmiaohe@huawei.com> <20230715031729.2420338-2-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <33748ced-5fd3-f3f7-f358-ca016ca8ba36@huawei.com> Date: Mon, 17 Jul 2023 10:33:14 +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: 7bit X-Originating-IP: [10.174.151.185] 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 2023/7/15 11:50, Matthew Wilcox wrote: > On Sat, Jul 15, 2023 at 11:17:26AM +0800, Miaohe Lin wrote: >> Hwpoisoned dirty swap cache page is kept in the swap cache and there's >> simple interception code in do_swap_page() to catch it. But when trying >> to swapoff, unuse_pte() will wrongly install a general sense of "future >> accesses are invalid" swap entry for hwpoisoned swap cache page due to >> unaware of such type of page. The user will receive SIGBUS signal without >> expected BUS_MCEERR_AR payload. > > Have you observed this, or do you just think it's true? > >> +++ b/mm/swapfile.c >> @@ -1767,7 +1767,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, >> swp_entry_t swp_entry; >> >> dec_mm_counter(vma->vm_mm, MM_SWAPENTS); >> - if (hwposioned) { >> + /* Hwpoisoned swapcache page is also !PageUptodate. */ >> + if (hwposioned || PageHWPoison(page)) { > > This line makes no sense to me. How do we get here with PageHWPoison() > being true and hwposioned being false? hwposioned will be true iff ksm_might_need_to_copy returns -EHWPOISON. And there's PageUptodate check in ksm_might_need_to_copy before we can return -EHWPOISON: ksm_might_need_to_copy if (!PageUptodate(page)) return page; /* let do_swap_page report the error */ ^^^ Will return here because hwpoisoned swapcache page is !PageUptodate(cleared via me_swapcache_dirty()). Or am I miss something? Thanks.