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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 794ADC4338F for ; Wed, 11 Aug 2021 14:02:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5658D60551 for ; Wed, 11 Aug 2021 14:02:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232011AbhHKOCc (ORCPT ); Wed, 11 Aug 2021 10:02:32 -0400 Received: from foss.arm.com ([217.140.110.172]:51498 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230479AbhHKOCb (ORCPT ); Wed, 11 Aug 2021 10:02:31 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AE76C1063; Wed, 11 Aug 2021 07:02:07 -0700 (PDT) Received: from e123427-lin.cambridge.arm.com (unknown [10.57.39.227]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B09CF3F718; Wed, 11 Aug 2021 07:02:04 -0700 (PDT) Date: Wed, 11 Aug 2021 15:01:57 +0100 From: Lorenzo Pieralisi To: Ard Biesheuvel Cc: Christoph Hellwig , Linux Kernel Mailing List , "Rafael J. Wysocki" , ACPI Devel Maling List , Linux ARM , Veronika kabatova , Robin Murphy , Will Deacon , Hanjun Guo , Sudeep Holla , Catalin Marinas Subject: Re: [PATCH v2 1/3] ACPI: osl: Add __force attribute in acpi_os_map_iomem() cast Message-ID: <20210811140157.GA28658@e123427-lin.cambridge.arm.com> References: <20210726100026.12538-1-lorenzo.pieralisi@arm.com> <20210802152359.12623-2-lorenzo.pieralisi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Wed, Aug 11, 2021 at 12:40:28PM +0200, Ard Biesheuvel wrote: > On Tue, 10 Aug 2021 at 18:46, Christoph Hellwig wrote: > > > > On Mon, Aug 02, 2021 at 04:23:57PM +0100, Lorenzo Pieralisi wrote: > > > Add a __force attribute to the void* cast in acpi_os_map_iomem() > > > to prevent sparse warnings. > > > > Err, no. These annotation are there for a reason and need to > > be propagated instead. And independent of that a __force cast > > without a comment explaining it is a complete no-go. > > The whole problem we are solving here is that ACPI, being based on > x86, conflates MMIO mappings with memory mappings, and has been using > the same underlying infrastructure for either. On arm64, this is not > sufficient, given that the semantics of uncached memory vs device are > different (the former permits unaligned accesses and clear cacheline > instructions, but the latter doesn't). A recent optimization applied > to memcpy() on arm64 (which now relies more on unaligned accesses for > performance) has uncovered an issue where firmware tables being mapped > non-cacheable by the ACPI core will end up using device mappings, > which causes memcpy() to choke on their contents. > > So propagating the annotation makes no sense, as we are creating a > memory mapping using the iomem primitive. I wouldn't object to a > comment being added, but I think the context should have been obvious > to anyone who had bothered to look at the entire series. I can add a comment and respin. Basically a __force attribute is added to ignore a sparse warning that's been ignored for aeons anyway - I will add the rationale above. drivers/acpi/osl.c:379:17: warning: cast removes address space '__iomem' of expression