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 37981C0015E for ; Sun, 23 Jul 2023 02:23:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229844AbjGWCX1 (ORCPT ); Sat, 22 Jul 2023 22:23:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50598 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229545AbjGWCXZ (ORCPT ); Sat, 22 Jul 2023 22:23:25 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CA531BD4 for ; Sat, 22 Jul 2023 19:23:22 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4R7n8J2YSvzHnVL; Sun, 23 Jul 2023 10:20:48 +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; Sun, 23 Jul 2023 10:23:19 +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> <33748ced-5fd3-f3f7-f358-ca016ca8ba36@huawei.com> From: Miaohe Lin Message-ID: Date: Sun, 23 Jul 2023 10:23:18 +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: dggems703-chm.china.huawei.com (10.3.19.180) 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 2023/7/17 10:53, Matthew Wilcox wrote: > On Mon, Jul 17, 2023 at 10:33:14AM +0800, Miaohe Lin wrote: >> 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? > > Ah! So we don't even get to calling copy_mc_to_kernel(). That seems > like a bug in ksm_might_need_to_copy(), don't you think? Maybe this > would be a better fix: > > + if (PageHWPoison(page)) > + return ERR_PTR(-EHWPOISON); I'm preparing posting the v2. But I found this won't fix the issue if CONFIG_KSM is disabled. So the correct fix should be something like below? diff --git a/mm/ksm.c b/mm/ksm.c index 97a9627116fa..74804158ee02 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2794,6 +2794,8 @@ struct page *ksm_might_need_to_copy(struct page *page, anon_vma->root == vma->anon_vma->root) { return page; /* still no need to copy it */ } + if (PageHWPoison(page)) + return ERR_PTR(-EHWPOISON); if (!PageUptodate(page)) return page; /* let do_swap_page report the error */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 346e22b8ae97..3dcc9d92689c 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1744,7 +1744,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, struct page *swapcache; spinlock_t *ptl; pte_t *pte, new_pte, old_pte; - bool hwposioned = false; + bool hwposioned = PageHWPoison(page); int ret = 1; swapcache = page; Thanks.