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 6D535C43334 for ; Thu, 14 Jul 2022 10:09:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238076AbiGNKJz (ORCPT ); Thu, 14 Jul 2022 06:09:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231163AbiGNKJx (ORCPT ); Thu, 14 Jul 2022 06:09:53 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 796C34E854 for ; Thu, 14 Jul 2022 03:09:52 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Lk9DG6ThlzlVlr; Thu, 14 Jul 2022 18:08:14 +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; Thu, 14 Jul 2022 18:09:50 +0800 Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic_pte To: Axel Rasmussen , Mike Kravetz , Peter Xu CC: Andrew Morton , Muchun Song , Linux MM , LKML References: <20220712130542.18836-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <1a27f20c-ed69-398a-5e6d-bb7ec5f14f5f@huawei.com> Date: Thu, 14 Jul 2022 18:09:49 +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: dggems706-chm.china.huawei.com (10.3.19.183) 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 8:20, Axel Rasmussen wrote: > On Wed, Jul 13, 2022 at 4:36 PM Mike Kravetz wrote: >> >> On 07/13/22 15:46, Axel Rasmussen wrote: >>> I think there is a small mistake in this patch. >>> >>> Consider the non-minor-fault case. We have this block: >>> >>> /* Add shared, newly allocated pages to the page cache. */ >>> if (vm_shared && !is_continue) { >>> /* ... */ >>> } >>> >>> In here, we've added the newly allocated page to the page cache, and >>> we've set this page_in_pagecache flag to true. But we *do not* setup >>> rmap for this page in this block. I think in this case, the patch will >>> cause us to do the wrong thing: we should hugepage_add_new_anon_rmap() >>> further down, but with this patch we dup instead. >> >> I am not sure I follow. The patch from Miaohe Lin would not change any >> behavior in the 'if (vm_shared && !is_continue)' case. In this case >> both vm_shared and page_in_pagecache are true. >> >> IIUC, the patch would address the case where !vm_shared && is_continue. > > Ah, you're right, my interpretation of the various flags got mixed up > somewhere along the way. > > page_in_pagecache is equivalent to vm_shared in this function, > *except* when we have is_continue. Given that, I think this patch is > correct in the vm_shared case (no behavior change). In case of > !vm_shared && is_continue, I agree the patch is a correction to the > previous behavior. > >> >> On 07/12/22 21:05, 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. >>> >>> Fixes: f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE ioctl") >>> Signed-off-by: Miaohe Lin >>> --- >>> mm/hugetlb.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index 8d379e03f672..b232e1508e49 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -6038,7 +6038,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, >>> if (!huge_pte_none_mostly(huge_ptep_get(dst_pte))) >>> goto out_release_unlock; >>> >>> - if (vm_shared) { >>> + if (page_in_pagecache) { >>> page_dup_file_rmap(page, true); Many thanks for your comments. As discussed in another thread, we might call page_dup_file_rmap for newly allocated page (regardless of this patch). So should we come up a seperate patch to call page_add_file_rmap here instead? Thanks. >>> } else { >>> ClearHPageRestoreReserve(page); >> >> -- >> Mike Kravetz > . >