From patchwork Wed Feb 10 21:21:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12081771 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=ham 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 BDFDFC433E0 for ; Wed, 10 Feb 2021 21:24:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B04D64ED3 for ; Wed, 10 Feb 2021 21:24:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233704AbhBJVYY (ORCPT ); Wed, 10 Feb 2021 16:24:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233404AbhBJVXF (ORCPT ); Wed, 10 Feb 2021 16:23:05 -0500 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEB7BC0617AA for ; Wed, 10 Feb 2021 13:22:18 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id g17so1291646ybh.4 for ; Wed, 10 Feb 2021 13:22:18 -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=C7eX4+NVGX5He9yBXKDzK09THiAFk9zxs8Mq4BgC9+k=; b=X4O2XnKeTyP1mrCdcCUv43l+RzH7IHrvPnQey/wsi4M+B7W6hzZlGZRvvKHgHPwxwy /WvTVU9Ez2URRDEtOOJilnHqyhVt6olC/GaNJXdnpvVpPBeGB4gNunb7ZQQAvUfzsdxe edZieAb5VYpDFXolL8aMA/zf1+cab8/dJJYDrbwRG+GaG11wlghI8k3l4/uai0ppkIOY VRGXu6go8MCoW4HFmNHNxwfTbMwbVHMUk2ma8RoEvXxXQ4B5PVnkOj5fjrgRZZ2y3LAP 0DBfUQeu/ImT99KF9thtVNcUbahpM0amXl0cGg6p/tFca2fEUDbwL7TN4RyPqcPqmPCr FDgQ== 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=C7eX4+NVGX5He9yBXKDzK09THiAFk9zxs8Mq4BgC9+k=; b=JrrmgOW0IvsvxKmk3uKn5+gUA75vVct91+Z7sSt3BFevChC//kSiApH/VopBPUAPM8 7cRpQtc3qCh/B64cqw6VO2cnXJ7xsukAgYcev22WiyMqaG9A7M1tjJipL092rG8gYbFN X23sxRvfW5c8zOT+aJJxQVrf+9lz01S3NUHcOPSOGR5zg0J/cCyK2GypU2k4qyIPrNeQ IggJ0whpSUE3ycEqmSS3dNOm2J51jJCLWaU3QFCIK3+wpoKsgE1usR2B6D8pe//yDAcn ZCg/KMCzPsqR2b8z3ifLsHeULuhF/Iy+m4kUyXtF6dp5zQ6Vzu27AE1oSNEtNltYnxYZ 33Ug== X-Gm-Message-State: AOAM532fO3XBcUO+Sp3t09vbl2jp3fpk9jPgz/1wC3pd7dbhtx6GoYhu 8/xWoGxhtSewnRg/skNge86VLkW5JFImTOMwBoCY X-Google-Smtp-Source: ABdhPJwagtVWNE35dh8EXmqH56OhS+dAouO564OVOUkNaVQb6+9yLc/FG1bX+ngeJuwo0ZOZsUjMFDiVvTAXntctl3Gj Sender: "axelrasmussen via sendgmr" X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:94ee:de01:168:9f20]) (user=axelrasmussen job=sendgmr) by 2002:a25:cc46:: with SMTP id l67mr7659356ybf.16.1612992138150; Wed, 10 Feb 2021 13:22:18 -0800 (PST) Date: Wed, 10 Feb 2021 13:21:56 -0800 In-Reply-To: <20210210212200.1097784-1-axelrasmussen@google.com> Message-Id: <20210210212200.1097784-7-axelrasmussen@google.com> Mime-Version: 1.0 References: <20210210212200.1097784-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.30.0.478.g8a0d178c01-goog Subject: [PATCH v5 06/10] 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_Koutn=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 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)