From patchwork Mon Mar 1 22:27:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12110733 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 1D9E0C433E0 for ; Mon, 1 Mar 2021 22:40:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D39E760202 for ; Mon, 1 Mar 2021 22:40:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238114AbhCAWcQ (ORCPT ); Mon, 1 Mar 2021 17:32:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57396 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244932AbhCAW2U (ORCPT ); Mon, 1 Mar 2021 17:28:20 -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 4E9D3C061797 for ; Mon, 1 Mar 2021 14:27:40 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id u1so20472489ybu.14 for ; Mon, 01 Mar 2021 14:27:40 -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=Ffolv6cCxRHUvURj2O7pa1bwsyAQ1T5kdza2OAkkouY=; b=OqWULVsjc5kG1tSiKzdPQ6lmZhTxIus8AFl8m9sfc24TVgVwz+5dJB9LVZ92SGAztl M1nnT5eqN8K86Cbg+aZbMvtu+VsW5UwayjcttoCx9NyGETzAEsuZ206lgRVsAfTL3pP0 BUSXsrDQSABJsXlXkpzuhE3HmrUVv7mf6okeR275r+qQlu/EWudrDmmc+gwTnDmONdmt qAKuZwItPa/F/QHolBwTCLgzowfYc6iWaevajuM+UoGhnj6Y+5ctlwg8YlPTFZbQ9hP2 HQMwj8mxoXk0G2t2xhmk5WVUczMKf52EW+fioAByRJTMOPvXR3agMuDhmHFn36hUBmol NmJw== 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=Ffolv6cCxRHUvURj2O7pa1bwsyAQ1T5kdza2OAkkouY=; b=RaBQ8LWHTppSa/6muVwe8q6AUTE98kTv4AFy8FhnsJsZsDvr7vNPG6bZ4VVEKOQYB1 JQ331HqLj2eAlC9h1BYlNpjMHSU7ltWldlW/MUHZbQ735KCyGw3EEwyy/yuDJ338Ve1L 920X4Y2Zun/xnpLVqRUo090yEpsOd2O/eFMhjYbWTVSUjXsYymLlZWucCEsSc7kevQwx MaAwb1U7SmUie1Bz/waB72QNX88J44qzCfywhDzRwWOxoV2sxqc9WEmk8X2VRLLmCS+p 3j97rhn4XgdixfVqwa+3u0QWCeAfOJjclIX+pQo3XJs2YGaf9gsec3spX892zraYsnVw ZQgw== X-Gm-Message-State: AOAM53362ScWJUCgFuP6OaCYyRMok934fCoUiSuZtuIBqw/6dBuOo232 5MSdNCEhTHVrbQY5g/E2NGl5tcK54ktJF0KXOZpj X-Google-Smtp-Source: ABdhPJzc5y7AU15P9PCUuTuAnbP63qIvfhyNPhEpq27PTqPFwjyDNYHkSqeT60bmJ8CafzW2xk2sNBegVQIFa0LllhKV Sender: "axelrasmussen via sendgmr" X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:1998:8165:ca50:ab8d]) (user=axelrasmussen job=sendgmr) by 2002:a25:e785:: with SMTP id e127mr26698696ybh.451.1614637659522; Mon, 01 Mar 2021 14:27:39 -0800 (PST) Date: Mon, 1 Mar 2021 14:27:24 -0800 In-Reply-To: <20210301222728.176417-1-axelrasmussen@google.com> Message-Id: <20210301222728.176417-3-axelrasmussen@google.com> Mime-Version: 1.0 References: <20210301222728.176417-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.30.1.766.gb4fecdf3b7-goog Subject: [PATCH v9 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_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 Reviewed-by: Mike Kravetz 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)