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 48360C433EF for ; Fri, 15 Jul 2022 03:56:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241084AbiGOD4p (ORCPT ); Thu, 14 Jul 2022 23:56:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbiGOD4o (ORCPT ); Thu, 14 Jul 2022 23:56:44 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45B9565583 for ; Thu, 14 Jul 2022 20:56:43 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LkctV5XsQzkX3S; Fri, 15 Jul 2022 11:54:26 +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; Fri, 15 Jul 2022 11:56:41 +0800 Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic_pte To: Peter Xu , Axel Rasmussen CC: Andrew Morton , , , , References: <20220712130542.18836-1-linmiaohe@huawei.com> <20220713102357.8328614813db01b569650ffd@linux-foundation.org> From: Miaohe Lin Message-ID: <402ae708-4c86-8feb-75c4-9339e1deac3b@huawei.com> Date: Fri, 15 Jul 2022 11:56:40 +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: 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 2022/7/14 23:52, Peter Xu wrote: > On Thu, Jul 14, 2022 at 05:59:53PM +0800, Miaohe Lin wrote: >> On 2022/7/14 1:23, Andrew Morton wrote: >>> On Tue, 12 Jul 2022 21:05:42 +0800 Miaohe Lin wrote: >>> >>>> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page >>>> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called >>>> for them mistakenly because they're not vm_shared. This will corrupt the >>>> page->mapping used by page cache code. >>> >>> Well that sounds bad. And theories on why this has gone unnoticed for >>> over a year? I assume this doesn't have coverage in our selftests? >> >> As discussed in another thread, when minor fault handling is proposed, only >> VM_SHARED vma is expected to be supported. And the test case is also missing. > > Yes, after this patch applied it'll be great to have the test case covering > private mappings too. > > It's just that it'll be a bit more than setting test_uffdio_minor=1 for > "hugetlb" test. In hugetlb_allocate_area() we'll need to setup the alias > too for !shared case, it'll be a bit challenging since currently we're > using anonymous hugetlb mappings for private tests, and I'm not sure > whether we'll need the hugetlb path back just like what we have with > "hugetlb_shared" tests. I'm afraid not. When minor fault handling is proposed, only VM_SHARED vma is expected to be supported. It seems it's hard to image how one might benefit from using it with a private mapping. But I'm not sure as I'm still a layman in userfaultfd now. Any further suggestions? > Thanks!