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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 351D4C43381 for ; Sun, 17 Feb 2019 08:35:58 +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 AB5992075C for ; Sun, 17 Feb 2019 08:35:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB5992075C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au 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 442L1R4lvZzDqLL for ; Sun, 17 Feb 2019 19:35:55 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (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 442Kzd50VPzDqDf for ; Sun, 17 Feb 2019 19:34:21 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 442Kzd3snhz9sLw; Sun, 17 Feb 2019 19:34:21 +1100 (AEDT) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPSA id 442Kzd1w66z9sDX; Sun, 17 Feb 2019 19:34:21 +1100 (AEDT) From: Michael Ellerman To: Balbir Singh , Segher Boessenkool Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present() In-Reply-To: <20190217062333.GC31125@350D> References: <20190214062339.7139-1-mpe@ellerman.id.au> <20190216105511.GA31125@350D> <20190216142206.GE14180@gate.crashing.org> <20190217062333.GC31125@350D> Date: Sun, 17 Feb 2019 19:34:20 +1100 Message-ID: <87ef86dd9v.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain 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, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, aneesh.kumar@linux.vnet.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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. cheers