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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D95F6C433F5 for ; Tue, 19 Apr 2022 11:21:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 553608D0065; Tue, 19 Apr 2022 07:21:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5021F8D0047; Tue, 19 Apr 2022 07:21:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3CB2C8D0065; Tue, 19 Apr 2022 07:21:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.26]) by kanga.kvack.org (Postfix) with ESMTP id 2A95E8D0047 for ; Tue, 19 Apr 2022 07:21:09 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id EB1D662375 for ; Tue, 19 Apr 2022 11:21:08 +0000 (UTC) X-FDA: 79373387016.25.4FB8798 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf16.hostedemail.com (Postfix) with ESMTP id 2D864180015 for ; Tue, 19 Apr 2022 11:21:07 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KjLpt61nYzCr6X; Tue, 19 Apr 2022 19:16:38 +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, 19 Apr 2022 19:21:02 +0800 Subject: Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap read fails To: David Hildenbrand , CC: , , , , , , , , , , , , References: <20220416030549.60559-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <1b614ac3-02c0-ec66-b51a-e9b7e1a375ad@huawei.com> Date: Tue, 19 Apr 2022 19:21:02 +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: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 2D864180015 X-Stat-Signature: wwnrk6wk9bqy93pdzashfbonyj9qsrhg Authentication-Results: imf16.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf16.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-HE-Tag: 1650367267-804510 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/4/19 15:37, David Hildenbrand wrote: > On 16.04.22 05:05, Miaohe Lin wrote: >> There is a bug in unuse_pte(): when swap page happens to be unreadable, >> page filled with random data is mapped into user address space. In case >> of error, a special swap entry indicating swap read fails is set to the >> page table. So the swapcache page can be freed and the user won't end up >> with a permanently mounted swap because a sector is bad. And if the page >> is accessed later, the user process will be killed so that corrupted data >> is never consumed. On the other hand, if the page is never accessed, the >> user won't even notice it. >> >> Signed-off-by: Miaohe Lin >> --- >> v2: >> use special swap entry to avoid permanently mounted swap >> free the bad page in swapcache >> --- >> include/linux/swap.h | 7 ++++++- >> include/linux/swapops.h | 10 ++++++++++ >> mm/memory.c | 5 ++++- >> mm/swapfile.c | 11 +++++++++++ >> 4 files changed, 31 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/swap.h b/include/linux/swap.h >> index d112434f85df..03c576111737 100644 >> --- a/include/linux/swap.h >> +++ b/include/linux/swap.h >> @@ -55,6 +55,10 @@ static inline int current_is_kswapd(void) >> * actions on faults. >> */ >> >> +#define SWAP_READ_ERROR_NUM 1 >> +#define SWAP_READ_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \ >> + SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \ >> + SWP_PTE_MARKER_NUM) > > Does anything speak against reusing the hwpoison marker? At least from a > program POV it's similar "the previously well defined content at this > user space address is no longer readable/writable". Looks like a good idea. :) > > I recall that we can just set the pfn to 0 for the hwpoison marker. > > There is e.g., check_hwpoisoned_entry() and it just stops if it finds > "pfn=0". Do you mean that we should set the pfn to 0 for the hwpoison marker so that we can distinguish swapin error case from real hwpoison case? > > Will try to do this in next version. Thanks a lot!