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 76C47C4727C for ; Tue, 29 Sep 2020 13:49:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DC2EB207C4 for ; Tue, 29 Sep 2020 13:49:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="YWvZewRv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC2EB207C4 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 0E0888E0003; Tue, 29 Sep 2020 09:49:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 08FF48E0001; Tue, 29 Sep 2020 09:49:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9A1A8E0003; Tue, 29 Sep 2020 09:49:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0090.hostedemail.com [216.40.44.90]) by kanga.kvack.org (Postfix) with ESMTP id CBB068E0001 for ; Tue, 29 Sep 2020 09:49:40 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 98433181AE869 for ; Tue, 29 Sep 2020 13:49:40 +0000 (UTC) X-FDA: 77316231720.25.side28_1700b492718a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin25.hostedemail.com (Postfix) with ESMTP id ACD6D1802588C for ; Tue, 29 Sep 2020 13:49:38 +0000 (UTC) X-HE-Tag: side28_1700b492718a X-Filterd-Recvd-Size: 5049 Received: from mail-oi1-f194.google.com (mail-oi1-f194.google.com [209.85.167.194]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Tue, 29 Sep 2020 13:49:37 +0000 (UTC) Received: by mail-oi1-f194.google.com with SMTP id w16so5512106oia.2 for ; Tue, 29 Sep 2020 06:49:37 -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=uf55h5Im87Thv0CvH7P0y872ufq4n52JjgwdZSbMlsE=; b=YWvZewRv9EPKGFMnrlX58gFAN4LNRwvpGbFM90qagfwzOhq0xOTQNlNS+0+/UZRUXl Q7O5w9O42x2fVh6uUAi4MXMRUBrKtvPQ47jSBSlQYgk1VuwO5B/SEVy9ORLiy61AlAHw +UzixFrJbSnGdRS8QXuZuySULzOKUs/8R3kIgIbvZ7ebPA5UfZeQv1RFr0FfPnXMg0bL bHxh0w1kGfiqwbe9bqgEIcuhrl3d1BBCkFUWfqeddsGe8Bze8qiCFcdUboFW+w1ha7Ek Y7rSAQOzrp/Pjaj+giqaZMqJIQ8LErSJVTTUhTPFN5cmDq27q8qtmhYOLdO+wydX+nS0 zYfg== 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=uf55h5Im87Thv0CvH7P0y872ufq4n52JjgwdZSbMlsE=; b=hhd+LIEsghKdul6YBtqmaS5lA9Oyg3WIk44UstNK+E4JC0kdD2YUi08QuBWZvjisqg P0zHHF0UegWB0Ixi7opuxYeMsEI7D6oeCICk8SwaEsPnXmSqdNHG2IEHd7RpIy/GcRty xDgIfkgp0mBKJbrWIlALE61kaXwOqSSo+7p3dG5Vl7HQ96h3l1lDzbwiaRP/OC4zIvF2 H4ofm4wap53Smdfsj1bXv2EjAz06wZnnNKc4hDfpKR+u84XxDX/M8XCYzLFxoFSP+GWX TGz5bmX2vKlwJimOCPgWbTDvT2hp1NU7UJVgDjKdFXXkvTa+vnQM+NXIsWOnqQExo7q4 xUrg== X-Gm-Message-State: AOAM530aEDoe7g9wpMpiMgnNVRuN3mqg8b/BdtSmG34rKzlbVLSCCu6x 8GFkEWUC80mL+Vo5/qobISUI4EFyof8eKJ9rABVguQ== X-Google-Smtp-Source: ABdhPJxiJi8hWBBZVcllFLyB/VLfKmBGpjW01B6eYyc4+D70if0keiWc+WE0jU5wtu+kUc8X4oTDsf54W+9c0iy9kFM= X-Received: by 2002:aca:5158:: with SMTP id f85mr2718140oib.121.1601387375957; Tue, 29 Sep 2020 06:49:35 -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: Marco Elver Date: Tue, 29 Sep 2020 15:49:24 +0200 Message-ID: Subject: Re: [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure To: Andrey Konovalov 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, 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.