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 9E33EC433F5 for ; Thu, 16 Sep 2021 07:22:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 767B261185 for ; Thu, 16 Sep 2021 07:22:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234759AbhIPHXW (ORCPT ); Thu, 16 Sep 2021 03:23:22 -0400 Received: from gate.crashing.org ([63.228.1.57]:33905 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232254AbhIPHXU (ORCPT ); Thu, 16 Sep 2021 03:23:20 -0400 Received: from ip6-localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 18G7GUXH031599; Thu, 16 Sep 2021 02:16:36 -0500 Message-ID: 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 17:16:30 +1000 In-Reply-To: <2c0fd775625c76c4dd09b3e923da4405a003f3bd.camel@kernel.crashing.org> References: <62b33ca839f3d1d7d4b64b6f56af0bbe4d2c9057.1631716292.git.christophe.leroy@csgroup.eu> <2c0fd775625c76c4dd09b3e923da4405a003f3bd.camel@kernel.crashing.org> 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 Thu, 2021-09-16 at 17:15 +1000, Benjamin Herrenschmidt wrote: > 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 ? Ah I saw your other one about fbdev... Ok what about you do that in a if (!user_mode(regs)) ? Indeed the kernel should not do that. Cheers, Ben.