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 X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0083C433DB for ; Thu, 25 Feb 2021 00:29:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7242B64F10 for ; Thu, 25 Feb 2021 00:29:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236426AbhBYA2l (ORCPT ); Wed, 24 Feb 2021 19:28:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42908 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236410AbhBYA2b (ORCPT ); Wed, 24 Feb 2021 19:28:31 -0500 Received: from mail-qk1-x749.google.com (mail-qk1-x749.google.com [IPv6:2607:f8b0:4864:20::749]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89834C06178A for ; Wed, 24 Feb 2021 16:27:12 -0800 (PST) Received: by mail-qk1-x749.google.com with SMTP id 19so3152631qks.13 for ; Wed, 24 Feb 2021 16:27:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=Gqbdv7dcKJ3HCSbhGAkcVMLKp5XjaZ2pyZBQ0WD1HYc=; b=iQABgmB2nLQqaKFyd+0m8gvgul2Nt+XEMSupc3YU+qI9MdQ6eucQVi37eJUoliHxGc OCA3NnqnU0jVrAPr6wJdk3zwxFyRkq+GqYdIMH7GKD9BkNJKUAZdzcpJ/WYkwuIVfhHo MaUfU84qw3yu0dvwnEga90NViMOUtE5V3Qicxd5SqkolYKOv31XWFq6wa8zduh/NmSgY XY84n067XFrVpjAncfw/6qjH75qZVlt6Z+XyGvVZeJhdTxVXr8gGI+LIbtVIAJ2TWosG GNO1H5CyC1zMdrXCjCEpGj8ujleA4lr68NUOhYwhlhplb8jOusKFkKYl49EDsMiVJI9D kVng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=Gqbdv7dcKJ3HCSbhGAkcVMLKp5XjaZ2pyZBQ0WD1HYc=; b=KINLOuEubMQkInq89U/HpjQsHdnvEaD0zdxHylXvNaqYp2Ah4QF/+5LGaDziTLttNu /hgsl2jFoi4SBnW8Q+6XPpIilh/QY3mQfeESYyMFGBDP4eaondiwiHxYyaeh0g7nX/4A xZra6y56pSsiq0xtXVkLNjG7MXSPALVEtkwgZOnTcQIAX/+1NMIDwjx2W1+v3D7tywqX //VSKG5PR0yPIKj9t6cpkYj6Ob9MTb4o7XCH75cyBTKcazGFaY+EhUum14Clpw5UIOsS YT6kvG2Gl8q+3ICdIhovsXoRV90i75780iYPuPfJEt1qoYaLw0CCO0VLHP64LpCUlAOe U4lg== X-Gm-Message-State: AOAM531mbSXq3GFuSRXktxcOSvYjEVTn7dp4wj0UJ+hbb7B9+SmWyVJj 7mzjmMHsnmsmwkZ9YuaDxy5Ow0GvEPdJKiHQ1NbA X-Google-Smtp-Source: ABdhPJzA2CyX9smbu/vAvGixwBcY7izPD9oc6hVVChcH0GmIKCU5YaZZlii7h51Djyv6Qa6Kto2hlehC23SMRVOPwSYi Sender: "axelrasmussen via sendgmr" X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:a5fd:f848:2fdf:4651]) (user=axelrasmussen job=sendgmr) by 2002:a05:6214:941:: with SMTP id dn1mr237760qvb.61.1614212831623; Wed, 24 Feb 2021 16:27:11 -0800 (PST) Date: Wed, 24 Feb 2021 16:26:54 -0800 In-Reply-To: <20210225002658.2021807-1-axelrasmussen@google.com> Message-Id: <20210225002658.2021807-3-axelrasmussen@google.com> Mime-Version: 1.0 References: <20210225002658.2021807-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.30.0.617.g56c4b15f3c-goog Subject: [PATCH v8 2/6] userfaultfd: disable huge PMD sharing for MINOR registered VMAs From: Axel Rasmussen To: Alexander Viro , Alexey Dobriyan , Andrea Arcangeli , Andrew Morton , Anshuman Khandual , Catalin Marinas , Chinwen Chang , Huang Ying , Ingo Molnar , Jann Horn , Jerome Glisse , Lokesh Gidra , "Matthew Wilcox (Oracle)" , Michael Ellerman , "=?UTF-8?q?Michal=20Koutn=C3=BD?=" , Michel Lespinasse , Mike Kravetz , Mike Rapoport , Nicholas Piggin , Peter Xu , Shaohua Li , Shawn Anastasio , Steven Rostedt , Steven Price , Vlastimil Babka Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Adam Ruprecht , Axel Rasmussen , Cannon Matthews , "Dr . David Alan Gilbert" , David Rientjes , Mina Almasry , Oliver Upton Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org As the comment says: for the MINOR fault use case, although the page might be present and populated in the other (non-UFFD-registered) half of the mapping, it may be out of date, and we explicitly want userspace to get a minor fault so it can check and potentially update the page's contents. Huge PMD sharing would prevent these faults from occurring for suitably aligned areas, so disable it upon UFFD registration. Reviewed-by: Peter Xu Signed-off-by: Axel Rasmussen --- include/linux/userfaultfd_k.h | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 0390e5ac63b3..e060d5f77cc5 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -56,12 +56,19 @@ static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, } /* - * Never enable huge pmd sharing on uffd-wp registered vmas, because uffd-wp - * protect information is per pgtable entry. + * Never enable huge pmd sharing on some uffd registered vmas: + * + * - VM_UFFD_WP VMAs, because write protect information is per pgtable entry. + * + * - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults for + * VMAs which share huge pmds. (If you have two mappings to the same + * underlying pages, and fault in the non-UFFD-registered one with a write, + * with huge pmd sharing this would *also* setup the second UFFD-registered + * mapping, and we'd not get minor faults.) */ static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) { - return vma->vm_flags & VM_UFFD_WP; + return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); } static inline bool userfaultfd_missing(struct vm_area_struct *vma) -- 2.30.0.617.g56c4b15f3c-goog