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 4AD7FC433E0 for ; Fri, 22 Jan 2021 21:50:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0BD9C23B16 for ; Fri, 22 Jan 2021 21:50:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730178AbhAVVuB (ORCPT ); Fri, 22 Jan 2021 16:50:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58828 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728410AbhAVVcy (ORCPT ); Fri, 22 Jan 2021 16:32:54 -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 1717BC061353 for ; Fri, 22 Jan 2021 13:29:42 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id k7so6758785ybm.13 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=BQt7dI3pdjCG8gjDbRTY7HvBA11A/PEoIDm3XSy8/82VRcuAZRNfkdAH0RCdvJrAtb ETywEWRTaoi7TwpLLPJlZsdZIhAiPDy7LtpNpG7iP5mTQz9t/B2GQjG57c11RKI6Yc7k efM3oEajSCtLV0o3TJRN/S7EhsJ7CBjSCYifEca26G+sTujZJKxfrpRMcjqUgCm5ysn5 kzDWDiIknknWI/amCiNH6hGxLmODN7LT3Gk0+5CNUGN6FIKXZorqe0pJ9DMxmrdv9+WP PK6C7hNsOui+rMADeNNvDH1s4eJ1ZF9HwmeKV26FDLHhCPp74q+kRC17Vb/htbJOb5kx nLpA== X-Gm-Message-State: AOAM532vdZOLRCyJm9y28uWt6+XfzCsxVJMhgwEnbn/V5TlaZJ87el5B OYQV31ZnpIWsp3+BlwJIe/H6JTZ1LcOKOWUUnpzT 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=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 , Oliver Upton Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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) -- 2.30.0.280.ga3ce27912f-goog