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=-11.9 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 BABB9C4727C for ; Tue, 29 Sep 2020 14:02:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3284820848 for ; Tue, 29 Sep 2020 14:02:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ICA6SzbA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3284820848 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5C5FE8E0005; Tue, 29 Sep 2020 10:02:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 54EF98E0001; Tue, 29 Sep 2020 10:02:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 417648E0005; Tue, 29 Sep 2020 10:02:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0148.hostedemail.com [216.40.44.148]) by kanga.kvack.org (Postfix) with ESMTP id 265468E0001 for ; Tue, 29 Sep 2020 10:02:42 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 672945DED for ; Tue, 29 Sep 2020 14:02:41 +0000 (UTC) X-FDA: 77316264522.21.table05_070695e2718a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 26E171809B36F for ; Tue, 29 Sep 2020 14:02:07 +0000 (UTC) X-HE-Tag: table05_070695e2718a X-Filterd-Recvd-Size: 5374 Received: from mail-pg1-f194.google.com (mail-pg1-f194.google.com [209.85.215.194]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Tue, 29 Sep 2020 14:02:06 +0000 (UTC) Received: by mail-pg1-f194.google.com with SMTP id 197so3950549pge.8 for ; Tue, 29 Sep 2020 07:02:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uOc+wQKeR9iMQFVgCW+E9/Ju05nBU+r7vf7w3Aw84Jc=; b=ICA6SzbAiu6VABJCQFScgh79U4MndSkcqDW3g5W5hWg3zZokeLmgN1DikCyg1zZpuc ytzuCdUvwHamWYeHnB++JMh5g3TlQxrV/o/8xZF/xHIwZySNAAwzdoQIzy5De9LHWo6U BMBfxboBQWHt8uZNoYvhOfNxfSjML6dkbjweM/JdvSQvyOt6F6JQX8/KiCJEGndxMJFA 4+cfN9CU+CxIeSOyl35ohMsasFdUfxsmkZKg5S+SNx5y1fpGWSTHdLDWYkz7PssrOt5s 4uCyqU1ZHQYUksoC9BAI8IXErDlGxckP+s4vR/WVG8QzgT3+9WCTvU5sS083UFeNorbC Cjqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=uOc+wQKeR9iMQFVgCW+E9/Ju05nBU+r7vf7w3Aw84Jc=; b=BgO2Rj4jPdBINk4QHSO7DHBU1LfqLcMrHsl4RzgVY1kkECX02n+5reNzlPZhwnl6nI lu3c9/EtgfGiZkV2/uZLOP9aoYKdEk0Zu0awpxm/SqXhMtdxn43ZjwOCSKZFAWRDPaz3 /cCvTYEJpt73/+8qRYdITrPCmWW8ZozNdsXvg6iRkFePKAeW9/kSNPg3v9o6x1dpo7y/ hhDxJ3cm12ZNhDx8SnvF8h9CfKf7vTrnlyGy/ZRAc1pXEGCVCGdF696b6XpP4MLBoMnQ OeXHN6+WEF1C3YumKnNmQb0WTIxNotrBa3eZPmV1wb/oLbR2C0aCaJILZNQKzm9BXQPn sfLA== X-Gm-Message-State: AOAM532jgsRuE9oNJpkW+BV5AuA2Oyie/+p5iI5xV4UVnnAvRJ9JdUJn affFWs14K+8zh8u/rDF+Kb/OeQIK8nZtQRInrD75dQ== X-Google-Smtp-Source: ABdhPJwm1SXbN9WMtge+tP0QBzrJvVif3aI8JVZkATFmqRV0dQwnUblP4/Bf6oL5wqW897E/yTrBLlA/qlbEAG5OBIA= X-Received: by 2002:a62:1d51:0:b029:13e:d13d:a0fc with SMTP id d78-20020a621d510000b029013ed13da0fcmr4462384pfd.24.1601388124642; Tue, 29 Sep 2020 07:02:04 -0700 (PDT) MIME-Version: 1.0 References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-2-elver@google.com> <20200929131135.GA2822082@elver.google.com> In-Reply-To: From: Andrey Konovalov Date: Tue, 29 Sep 2020 16:01:52 +0200 Message-ID: Subject: Re: [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure To: Marco Elver Cc: Andrew Morton , Alexander Potapenko , "H. Peter Anvin" , "Paul E . McKenney" , Andrey Ryabinin , Andy Lutomirski , Borislav Petkov , Catalin Marinas , Christoph Lameter , Dave Hansen , David Rientjes , Dmitry Vyukov , Eric Dumazet , Greg Kroah-Hartman , Hillf Danton , Ingo Molnar , Jann Horn , Jonathan Cameron , Jonathan Corbet , Joonsoo Kim , Kees Cook , Mark Rutland , Pekka Enberg , Peter Zijlstra , SeongJae Park , Thomas Gleixner , Vlastimil Babka , Will Deacon , "the arch/x86 maintainers" , "open list:DOCUMENTATION" , LKML , kasan-dev , Linux ARM , Linux Memory Management List Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 29, 2020 at 3:49 PM Marco Elver wrote: > > On Tue, 29 Sep 2020 at 15:48, Andrey Konovalov wrote: > > On Tue, Sep 29, 2020 at 3:11 PM Marco Elver wrote: > > > > > > On Tue, Sep 29, 2020 at 02:42PM +0200, Andrey Konovalov wrote: > > > [...] > > > > > + */ > > > > > + index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; > > > > > > > > Why do we subtract 1 here? We do have the metadata entry reserved for something? > > > > > > Above the declaration of __kfence_pool it says: > > > > > > * We allocate an even number of pages, as it simplifies calculations to map > > > * address to metadata indices; effectively, the very first page serves as an > > > * extended guard page, but otherwise has no special purpose. > > > > > > Hopefully that clarifies the `- 1` here. > > > > So there are two guard pages at the beginning and only then a page > > that holds an object? > > Yes, correct. OK, I see. This isn't directly clear from the comment though, at least for me :)