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 CB48AC38142 for ; Wed, 1 Feb 2023 01:23:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230390AbjBABXe (ORCPT ); Tue, 31 Jan 2023 20:23:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229962AbjBABXc (ORCPT ); Tue, 31 Jan 2023 20:23:32 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97AAD2DE6E for ; Tue, 31 Jan 2023 17:23:30 -0800 (PST) Received: from dggpemm500001.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4P63z95QwVznVDY; Wed, 1 Feb 2023 09:21:25 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Wed, 1 Feb 2023 09:23:27 +0800 Message-ID: Date: Wed, 1 Feb 2023 09:23:27 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH -next resend v3] mm: hwposion: support recovery from ksm_might_need_to_copy() Content-Language: en-US To: Miaohe Lin , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "tony.luck@intel.com" , "linux-kernel@vger.kernel.org" , David Hildenbrand References: <20221213030557.143432-1-wangkefeng.wang@huawei.com> <20221213120523.141588-1-wangkefeng.wang@huawei.com> <20221216014729.GA2116060@hori.linux.bs1.fc.nec.co.jp> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/12/17 10:24, Miaohe Lin wrote: > On 2022/12/16 9:47, HORIGUCHI NAOYA(堀口 直也) wrote: >> On Tue, Dec 13, 2022 at 08:05:23PM +0800, Kefeng Wang wrote: >>> When the kernel copy a page from ksm_might_need_to_copy(), but runs >>> into an uncorrectable error, it will crash since poisoned page is >>> consumed by kernel, this is similar to Copy-on-write poison recovery, >> >> Maybe you mean "this is similar to the issue recently fixed by >> Copy-on-write poison recovery."? And if this sentence ends here, >> please put "." instead of ",". >> >>> When an error is detected during the page copy, return VM_FAULT_HWPOISON >>> in do_swap_page(), and install a hwpoison entry in unuse_pte() when >>> swapoff, which help us to avoid system crash. Note, memory failure on >>> a KSM page will be skipped, but still call memory_failure_queue() to >>> be consistent with general memory failure process. >> >> Thank you for the work. I have a few comment below ... > > Thanks both. > >>> - if (unlikely(!PageUptodate(page))) { >>> - pte_t pteval; >>> + if (hwposioned || !PageUptodate(page)) { >>> + swp_entry_t swp_entry; >>> >>> dec_mm_counter(vma->vm_mm, MM_SWAPENTS); >>> - pteval = swp_entry_to_pte(make_swapin_error_entry()); >>> - set_pte_at(vma->vm_mm, addr, pte, pteval); >>> - swap_free(entry); >>> + if (hwposioned) { >>> + swp_entry = make_hwpoison_entry(swapcache); >>> + page = swapcache; >> >> This might work for the process accessing to the broken page, but ksm >> pages are likely to be shared by multiple processes, so it would be >> much nicer if you can convert all mapping entries for the error ksm page >> into hwpoisoned ones. Maybe in this thorough approach, >> hwpoison_user_mappings() is updated to call try_to_unmap() for ksm pages. >> But it's not necessary to do this together with applying mcsafe-memcpy, >> because recovery action and mcsafe-memcpy can be done independently. >> > > I'm afraid leaving the ksm page in the cache will repeatedly trigger uncorrectable error for the > same page if ksm pages are shared by multiple processes. This might reach the hardware threshold > and result in fatal uncorrectable error (thus casuing system to panic). So IMHO it might be better > to check if page is hwpoisoned before calling ksm_might_need_to_copy() if above thorough approach > is not implemented. But I can easily be wrong. > Oh，missing this one，there are only two caller, one in do_swap_page(), it has already check whether the page is hwpoisoned or not, another is in unuse_pte() which only called from swapoff, it is not a hot patch, so I don't think it is an urgent requirement. Thanks.