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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 04629C43381 for ; Sat, 16 Feb 2019 14:27:33 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2CE3A21925 for ; Sat, 16 Feb 2019 14:27:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CE3A21925 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 441ssY2vBpzDqRR for ; Sun, 17 Feb 2019 01:27:29 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 441sqR4KLrzDqML for ; Sun, 17 Feb 2019 01:25:39 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) by bilbo.ozlabs.org (Postfix) with ESMTP id 441sqR2xscz8sw2 for ; Sun, 17 Feb 2019 01:25:39 +1100 (AEDT) Received: by ozlabs.org (Postfix) id 441sqR2Nkzz9s7h; Sun, 17 Feb 2019 01:25:39 +1100 (AEDT) Authentication-Results: ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 441sqQ3lgkz9s7T for ; Sun, 17 Feb 2019 01:25:38 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x1GEMUfJ030078; Sat, 16 Feb 2019 08:22:30 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x1GEMCDe030050; Sat, 16 Feb 2019 08:22:12 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Sat, 16 Feb 2019 08:22:12 -0600 From: Segher Boessenkool To: Balbir Singh Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present() Message-ID: <20190216142206.GE14180@gate.crashing.org> References: <20190214062339.7139-1-mpe@ellerman.id.au> <20190216105511.GA31125@350D> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190216105511.GA31125@350D> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: erhard_f@mailbox.org, jack@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, aneesh.kumar@linux.vnet.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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. Segher