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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 76679C43381 for ; Sun, 17 Feb 2019 21:56:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43EE12186A for ; Sun, 17 Feb 2019 21:56:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bXiPb+jj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726493AbfBQV4A (ORCPT ); Sun, 17 Feb 2019 16:56:00 -0500 Received: from mail-pl1-f193.google.com ([209.85.214.193]:42870 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726124AbfBQV4A (ORCPT ); Sun, 17 Feb 2019 16:56:00 -0500 Received: by mail-pl1-f193.google.com with SMTP id s1so7694319plp.9 for ; Sun, 17 Feb 2019 13:56:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=0wmxiqqk7vAqmoD3PZT4D63Pg1Meu3+th20mrox0DOk=; b=bXiPb+jjfszHalIcoiGQpr79ma8nHUzFESYIQEBjgvau7dlK3K1YyqqgkSGMsyuTAN oi91PYriZRkfrrF/V8hoEH4ml69BOQMHy86EvXVDzpK9wlww8T5kstXI0AMa8MqsFZ8z 3fG41To4sZ5ucp8bstPbknWBHxLatVJjmDIUOxEoyMVB0DeNxDf6UGbs1vZoXgD8zalt e3smdskO9nQgH11fmjyY+g0kVftd5WfwBF4+keK2y5lFUDra1xiQJRWIFzHKCkLDIkDh lSKxg/2+KIrGF33aPuTrHYpSBVlfKgeEfJ0cPEw/EYfT2hvYkkv1+NJtoq8qq+rwXG8Y Se8A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=0wmxiqqk7vAqmoD3PZT4D63Pg1Meu3+th20mrox0DOk=; b=GD1lJv1wJztFLqP5E9bRo+RV46180mRqiP/xv+Xe4vYS6oVrZO0J1VGiO/erQHOaJb 9IXcPbbavF681gqDKwFNuSsv260JdKvJkh5D5hA807/gzTulydrkJlpmwnmozOpkuhVd Kun+HaMLslQ5PW3e6x0LygQjNH5m28TWTbb6ukzf2ffZ1VcAVn70Erfd/zVSR3qi7la4 2SUUCfduZLQuwAkAmaHHu7SP4w+FIRyQGps6/rlHnWE8/S4MLUAK2NKzuhQebmO3NbYG h2rDITTGONxRHemY9H7LVI6iGxoXkOqCrQJZ5ZoB6A46djfsxBYfU/pMTJtZytkAIhxt KYkA== X-Gm-Message-State: AHQUAubTkwO8A6ku3iVUrCIKBSApn2RlD/GCKVVQivsFTGdjYKNvq5s7 u/gM3XVJTDJzuvW+l+7wLnE= X-Google-Smtp-Source: AHgI3IbqXw5YEK0XINbUyF5eYSMqG3seFTkN2WP0zeb+/N+xaXLutf2s82q5LgbDabqLwxuFqUbxag== X-Received: by 2002:a17:902:28e9:: with SMTP id f96mr21903651plb.169.1550440559472; Sun, 17 Feb 2019 13:55:59 -0800 (PST) Received: from localhost ([203.219.252.113]) by smtp.gmail.com with ESMTPSA id k74sm5381900pfb.172.2019.02.17.13.55.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 17 Feb 2019 13:55:58 -0800 (PST) Date: Mon, 18 Feb 2019 08:55:56 +1100 From: Balbir Singh To: Michael Ellerman Cc: Segher Boessenkool , erhard_f@mailbox.org, jack@suse.cz, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, aneesh.kumar@linux.vnet.ibm.com Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present() Message-ID: <20190217215556.GH31125@350D> References: <20190214062339.7139-1-mpe@ellerman.id.au> <20190216105511.GA31125@350D> <20190216142206.GE14180@gate.crashing.org> <20190217062333.GC31125@350D> <87ef86dd9v.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ef86dd9v.fsf@concordia.ellerman.id.au> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 17, 2019 at 07:34:20PM +1100, Michael Ellerman wrote: > Balbir Singh writes: > > On Sat, Feb 16, 2019 at 08:22:12AM -0600, Segher Boessenkool wrote: > >> Hi all, > >> > >> On Sat, Feb 16, 2019 at 09:55:11PM +1100, Balbir Singh wrote: > >> > On Thu, Feb 14, 2019 at 05:23:39PM +1100, Michael Ellerman wrote: > >> > > In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT > >> > > rather than just checking that the value is non-zero, e.g.: > >> > > > >> > > static inline int pgd_present(pgd_t pgd) > >> > > { > >> > > - return !pgd_none(pgd); > >> > > + return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); > >> > > } > >> > > > >> > > Unfortunately this is broken on big endian, as the result of the > >> > > bitwise && is truncated to int, which is always zero because > >> > >> (Bitwise "&" of course). > >> > >> > Not sure why that should happen, why is the result an int? What > >> > causes the casting of pgd_t & be64 to be truncated to an int. > >> > >> Yes, it's not obvious as written... It's simply that the return type of > >> pgd_present is int. So it is truncated _after_ the bitwise and. > >> > > > > Thanks, I am surprised the compiler does not complain about the truncation > > of bits. I wonder if we are missing -Wconversion > > Good luck with that :) > > What I should start doing is building with it enabled and then comparing > the output before and after commits to make sure we're not introducing > new cases. > Fair enough, my point was that the compiler can help out. I'll see what -Wconversion finds on my local build :) Balbir Singh.