From patchwork Fri Jan 22 21:29:23 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12040687 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 5E27AC433DB for ; Fri, 22 Jan 2021 21:35:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33C0423B06 for ; Fri, 22 Jan 2021 21:35:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729468AbhAVVfF (ORCPT ); Fri, 22 Jan 2021 16:35:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729656AbhAVVcK (ORCPT ); Fri, 22 Jan 2021 16:32:10 -0500 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14E58C061352 for ; Fri, 22 Jan 2021 13:29:42 -0800 (PST) Received: by mail-yb1-xb4a.google.com with SMTP id d38so6765242ybe.15 for ; Fri, 22 Jan 2021 13:29:42 -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=MPwAJ6+DP3gIY4R9V98gU/QUOgUfEvMZgCw03h5dW3o=; b=WYQGdSXW9Dowjq/tEtiJqYSTEnelLtZWHHwZiMQ94JhsG1GVc6oXRQMkpKu7eDAnHv NKg5GF6ig1ZApuH4agXonVwcgSdI+18UP1rEYDJjiagiX3nla69C6i534XagdKIa5rE/ stPFS97wq9OkZoeiz1rFi1x1kJZsS2k9umbO6YttlIBN6TmYynWgLi/QmC+NEZMItDTO 9ysUFg8CGvemV55rGYVD9R4kBsLZU/1kcscl/p0tmtk7bRUTGBNMM7r2jE3Eu/jv59Vv SJiRApl3UATIW3JdL0kjcsHrNtMWZkb94lqg3baFBxmKgHWZhyt+UWO78Fr7MO3m0ey5 ztKw== 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=MPwAJ6+DP3gIY4R9V98gU/QUOgUfEvMZgCw03h5dW3o=; b=uirOZrjhAlFlDBEHVygSpa08kjSE3MAHnrlEi08702qmvrZiPpZ4oPnAMrmST+BkED lM07BKlXQO6IPH1icBlupINppE06ZYc4Pe1wnvqXmoT+9LPqpu/fUsulOuMGsmPdG2W1 ratOBNMi2rW82T4z+ksGGlrDSzkYRoVR6dxCUlX2QcnqObc4jgxfbeccM2qnzEpo13fb W74VLyfIh6BPt6W+DmhDGT95+bIhB913gKPH1934q1m9I7XrfNHSDuxjxhszzrBpiNSU 1wxsM3EpGq5qo1YkZbVd0H/ZHP9rJFSubSaQR8cDe4KdKAxUZSMn9BIbovFhEoJlblNc 9vOA== X-Gm-Message-State: AOAM531z9chVbn0rdyTcFoH7dcjSj4F8J4ZO5A6MkRlpjTJc72LKJXCI rm92Uu/G1SSXq5rPSv4FV3Ikn/24j5c+5Ku7+Z+R X-Google-Smtp-Source: ABdhPJyHx4pF16cMtKv8VUHxhdr6uUrqdN7OvpRpZ9uoUtGCjEIg5DdoSNeVrersXyA8X3p5MBqwn7u8giCGUi5oMp4a Sender: "axelrasmussen via sendgmr" X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:f693:9fff:feef:c8f8]) (user=axelrasmussen job=sendgmr) by 2002:a25:c6d3:: with SMTP id k202mr9150649ybf.284.1611350981237; Fri, 22 Jan 2021 13:29:41 -0800 (PST) Date: Fri, 22 Jan 2021 13:29:23 -0800 In-Reply-To: <20210122212926.3457593-1-axelrasmussen@google.com> Message-Id: <20210122212926.3457593-7-axelrasmussen@google.com> Mime-Version: 1.0 References: <20210122212926.3457593-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.30.0.280.ga3ce27912f-goog Subject: [PATCH v2 6/9] 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 , 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 shared 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 | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 0390e5ac63b3..fb9abaeb4194 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -56,12 +56,18 @@ 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 we explicitly want minor faults to occur even + * when the other half of a shared mapping is populated (even though the page + * is there, in our use case it may be out of date, so userspace needs to + * check for this and possibly update it). */ 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)