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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 35EE9C433EF for ; Thu, 16 Sep 2021 07:18:09 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 5136B61185 for ; Thu, 16 Sep 2021 07:18:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5136B61185 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=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4H97hr6zp5z2yPs for ; Thu, 16 Sep 2021 17:18:04 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=benh@kernel.crashing.org; receiver=) Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 4H97hK2hKHz2xtw for ; Thu, 16 Sep 2021 17:17:36 +1000 (AEST) Received: from ip6-localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 18G7FGqQ031443; Thu, 16 Sep 2021 02:15:17 -0500 Message-ID: <2c0fd775625c76c4dd09b3e923da4405a003f3bd.camel@kernel.crashing.org> Subject: Re: [PATCH] powerpc: warn on emulation of dcbz instruction From: Benjamin Herrenschmidt To: Christophe Leroy , Paul Mackerras , Michael Ellerman Date: Thu, 16 Sep 2021 17:15:16 +1000 In-Reply-To: <62b33ca839f3d1d7d4b64b6f56af0bbe4d2c9057.1631716292.git.christophe.leroy@csgroup.eu> References: <62b33ca839f3d1d7d4b64b6f56af0bbe4d2c9057.1631716292.git.christophe.leroy@csgroup.eu> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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: Finn Thain , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Stan Johnson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, 2021-09-15 at 16:31 +0200, Christophe Leroy wrote: > dcbz instruction shouldn't be used on non-cached memory. Using > it on non-cached memory can result in alignment exception and > implies a heavy handling. > > Instead of silentely emulating the instruction and resulting in high > performance degradation, warn whenever an alignment exception is > taken due to dcbz, so that the user is made aware that dcbz > instruction has been used unexpectedly. > > Reported-by: Stan Johnson > Cc: Finn Thain > Signed-off-by: Christophe Leroy > --- > arch/powerpc/kernel/align.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/powerpc/kernel/align.c > b/arch/powerpc/kernel/align.c > index bbb4181621dd..adc3a4a9c6e4 100644 > --- a/arch/powerpc/kernel/align.c > +++ b/arch/powerpc/kernel/align.c > @@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs) > if (op.type != CACHEOP + DCBZ) > return -EINVAL; > PPC_WARN_ALIGNMENT(dcbz, regs); > + WARN_ON_ONCE(1); This is heavy handed ... It will be treated as an oops by various things uselessly spit out a kernel backtrace. Isn't PPC_WARN_ALIGNMENT enough ? Ben. 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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 74716C433F5 for ; Thu, 16 Sep 2021 07:20:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 569BC61185 for ; Thu, 16 Sep 2021 07:20:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234756AbhIPHWN (ORCPT ); Thu, 16 Sep 2021 03:22:13 -0400 Received: from gate.crashing.org ([63.228.1.57]:33881 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234568AbhIPHWL (ORCPT ); Thu, 16 Sep 2021 03:22:11 -0400 Received: from ip6-localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 18G7FGqQ031443; Thu, 16 Sep 2021 02:15:17 -0500 Message-ID: <2c0fd775625c76c4dd09b3e923da4405a003f3bd.camel@kernel.crashing.org> Subject: Re: [PATCH] powerpc: warn on emulation of dcbz instruction From: Benjamin Herrenschmidt To: Christophe Leroy , Paul Mackerras , Michael Ellerman Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Stan Johnson , Finn Thain Date: Thu, 16 Sep 2021 17:15:16 +1000 In-Reply-To: <62b33ca839f3d1d7d4b64b6f56af0bbe4d2c9057.1631716292.git.christophe.leroy@csgroup.eu> References: <62b33ca839f3d1d7d4b64b6f56af0bbe4d2c9057.1631716292.git.christophe.leroy@csgroup.eu> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2021-09-15 at 16:31 +0200, Christophe Leroy wrote: > dcbz instruction shouldn't be used on non-cached memory. Using > it on non-cached memory can result in alignment exception and > implies a heavy handling. > > Instead of silentely emulating the instruction and resulting in high > performance degradation, warn whenever an alignment exception is > taken due to dcbz, so that the user is made aware that dcbz > instruction has been used unexpectedly. > > Reported-by: Stan Johnson > Cc: Finn Thain > Signed-off-by: Christophe Leroy > --- > arch/powerpc/kernel/align.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/powerpc/kernel/align.c > b/arch/powerpc/kernel/align.c > index bbb4181621dd..adc3a4a9c6e4 100644 > --- a/arch/powerpc/kernel/align.c > +++ b/arch/powerpc/kernel/align.c > @@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs) > if (op.type != CACHEOP + DCBZ) > return -EINVAL; > PPC_WARN_ALIGNMENT(dcbz, regs); > + WARN_ON_ONCE(1); This is heavy handed ... It will be treated as an oops by various things uselessly spit out a kernel backtrace. Isn't PPC_WARN_ALIGNMENT enough ? Ben.