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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 97B5FC433F5 for ; Wed, 8 Sep 2021 07:45:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7603061179 for ; Wed, 8 Sep 2021 07:45:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350661AbhIHHqw (ORCPT ); Wed, 8 Sep 2021 03:46:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:46860 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233210AbhIHHqn (ORCPT ); Wed, 8 Sep 2021 03:46:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AE7FB61178 for ; Wed, 8 Sep 2021 07:45:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631087135; bh=PoRu+CAUg3VBGh79YA9R6PzT7K6KJSWvOcZiEPGVbg4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=hwdvwbkgODALuKqNxKonrXkN90p2soca7NQhu65Y+1qOx3s0t7h4goIMJ6sOv87Zs azNOOjusDsVEUvUV5Vvw40ZO5EJzRsC8RlDtREHOkZJhXAwTIGTsEIR1HIFSPnAIOk qL5+ObCrLt/0YPTqhoHjMkCZoAl340mJ7WJfIArRSH8I3mi7i5hcFE9bVMjSijyCPn 5/FueRobVSj11GcqGxjTold3u/G8ijrMA0jzwS+zkZNk8Du6fFun2uhcMAQxbMMQzr lyQgpg6bzBL875p8o0UhYDkO0Bj/Of9pdxbif59psmtrbLCVjnA7EOZTfPmUDHKgiU znPksNp8TNIbA== Received: by mail-ot1-f42.google.com with SMTP id x10-20020a056830408a00b004f26cead745so1807713ott.10 for ; Wed, 08 Sep 2021 00:45:35 -0700 (PDT) X-Gm-Message-State: AOAM530rmV2SxipXxOpXm4rwQYsMr8k4ApfZxk/ptfTV19vFNn93GEuS PB9EiAbs2JSXZODaKcjhx8s7aDztZmPIWIWuVZQ= X-Google-Smtp-Source: ABdhPJyOB6Ole19/mwc56/w3p7NNTf7L8aSx0sEgGjXiC1beNoWvMENfg8b+dzFoh7My+WOm51sTIvD4nhu65WLM/N4= X-Received: by 2002:a9d:12e2:: with SMTP id g89mr2050992otg.112.1631087135031; Wed, 08 Sep 2021 00:45:35 -0700 (PDT) MIME-Version: 1.0 References: <20210904060908.1310204-1-keithp@keithp.com> <20210907220038.91021-1-keithpac@amazon.com> <20210907220038.91021-5-keithpac@amazon.com> In-Reply-To: <20210907220038.91021-5-keithpac@amazon.com> From: Ard Biesheuvel Date: Wed, 8 Sep 2021 09:45:23 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 4/7] ARM: Use hack from powerpc to get current cpu number To: Keith Packard Cc: Linux Kernel Mailing List , Abbott Liu , Andrew Morton , Andrey Ryabinin , Anshuman Khandual , Arnd Bergmann , Bjorn Andersson , Christoph Lameter , Dennis Zhou , Geert Uytterhoeven , Jens Axboe , Joe Perches , Kees Cook , Krzysztof Kozlowski , Linus Walleij , Linux ARM , Linux Memory Management List , Manivannan Sadhasivam , Marc Zyngier , Masahiro Yamada , Mike Rapoport , Nathan Chancellor , Nick Desaulniers , Nick Desaulniers , Nicolas Pitre , Russell King , Tejun Heo , Thomas Gleixner , =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= , Valentin Schneider , Viresh Kumar , "Wolfram Sang (Renesas)" , YiFei Zhu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 8 Sept 2021 at 00:00, Keith Packard wrote: > > When we enable THREAD_INFO_IN_TASK, the cpu number will disappear from > thread_info and reappear in task_struct. As we cannot include > linux/sched.h in asm/smp.h, there's no way to use that struct type in > the raw_smp_processor_id macro. Instead, a hack from the powerpc code > is used. This pulls the TI_CPU offset out of asm-offsets.h and uses > that to find the cpu value. > > Signed-off-by: Keith Packard > --- > arch/arm/Makefile | 8 ++++++++ > arch/arm/include/asm/smp.h | 18 +++++++++++++++++- > 2 files changed, 25 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index 415c3514573a..6752995d2914 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -284,6 +284,14 @@ stack_protector_prepare: prepare0 > $(eval GCC_PLUGINS_CFLAGS += $(SSP_PLUGIN_CFLAGS)) > endif > > +ifdef CONFIG_SMP > +prepare: task_cpu_prepare > + > +PHONY += task_cpu_prepare > +task_cpu_prepare: prepare0 > + $(eval KBUILD_CFLAGS += -D_TI_CPU=$(shell awk '{if ($$2 == "TI_CPU") print $$3;}' include/generated/asm-offsets.h)) > +endif > + > all: $(notdir $(KBUILD_IMAGE)) > > > diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h > index d43b64635d77..f77ba3753bc4 100644 > --- a/arch/arm/include/asm/smp.h > +++ b/arch/arm/include/asm/smp.h > @@ -15,7 +15,23 @@ > # error " included in non-SMP build" > #endif > > -#define raw_smp_processor_id() (current_thread_info()->cpu) > +/* > + * This is particularly ugly: it appears we can't actually get the > + * definition of task_struct here, but we need access to the CPU this > + * task is running on, which is stored in task_struct when > + * THREAD_INFO_IN_TASK is set. Instead of using task_struct we're > + * using TI_CPU which is extracted from asm-offsets.h by kbuild to get > + * the current processor ID. > + * > + * This also needs to be safeguarded when building asm-offsets.s > + * because at that time TI_CPU is not defined yet. > + */ > +#ifndef _TI_CPU > +#define raw_smp_processor_id() (0) > +#else > +#define raw_smp_processor_id() \ > + (*(unsigned int *)((void *)current_thread_info() + _TI_CPU)) > +#endif > > struct seq_file; > As I stated before, I would really like to avoid using this hack - I don't think we need to.