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 6906EC433EF for ; Tue, 19 Apr 2022 11:21:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348317AbiDSLXu (ORCPT ); Tue, 19 Apr 2022 07:23:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242198AbiDSLXr (ORCPT ); Tue, 19 Apr 2022 07:23:47 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CFAC2657 for ; Tue, 19 Apr 2022 04:21:05 -0700 (PDT) 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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!