Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751877AbbBFKhO (ORCPT ); Fri, 6 Feb 2015 05:37:14 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:42243 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751182AbbBFKhL (ORCPT ); Fri, 6 Feb 2015 05:37:11 -0500 Date: Fri, 6 Feb 2015 10:36:53 +0000 From: Catalin Marinas To: Ard Biesheuvel Cc: Al Stone , Mark Langsdorf , "linaro-acpi@lists.linaro.org" , Will Deacon , "wangyijing@huawei.com" , Rob Herring , Timur Tabi , Daniel Lezcano , "linux-acpi@vger.kernel.org" , "msalter@redhat.com" , "phoenix.liyi@huawei.com" , Robert Richter , Jason Cooper , Arnd Bergmann , Marc Zyngier , "jcm@redhat.com" , Mark Brown , Bjorn Helgaas , "linux-arm-kernel@lists.infradead.org" , Ashwin Chaugule , Randy Dunlap , "Rafael J. Wysocki" , "linux-kernel@vger.kernel.org" , Olof Johansson Subject: Re: [Linaro-acpi] [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64 Message-ID: <20150206103653.GA23190@e104818-lin.cambridge.arm.com> References: <1422984576.18187.82.camel@deneb.redhat.com> <20150204112508.GB26006@e104818-lin.cambridge.arm.com> <1423066107.18187.99.camel@deneb.redhat.com> <20150204175734.GI26006@e104818-lin.cambridge.arm.com> <1423076294.18187.103.camel@deneb.redhat.com> <20150205104149.GA18158@e104818-lin.cambridge.arm.com> <1423144447.18187.110.camel@deneb.redhat.com> <54D39D6B.5090304@linaro.org> <20150205174826.GD21970@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2828 Lines: 54 On Thu, Feb 05, 2015 at 10:16:03PM +0000, Ard Biesheuvel wrote: > On 5 February 2015 at 17:48, Catalin Marinas wrote: > > On Thu, Feb 05, 2015 at 04:42:19PM +0000, Al Stone wrote: > >> On 02/05/2015 06:54 AM, Mark Salter wrote: > >> > On Thu, 2015-02-05 at 10:41 +0000, Catalin Marinas wrote: > >> >> On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote: > >> >>> On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote: > >> >>>> On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote: > >> >>>>> acpi_os_remap() is used to map ACPI tables. These tables may be in ram > >> >>>>> which are already included in the kernel's linear RAM mapping. So we > >> >>>>> need ioremap_cache to avoid two mappings to the same physical page > >> >>>>> having different caching attributes. > >> >>>> > >> >>>> What's the call path to acpi_os_ioremap() on such tables already in the > >> >>>> linear mapping? I can see an acpi_map() function which already takes > >> >>>> care of the RAM mapping case but there are other cases where > >> >>>> acpi_os_ioremap() is called directly. For example, > >> >>>> acpi_os_read_memory(), can it be called on both RAM and I/O? > >> >>> > >> >>> acpi_map() is the one I've seen. > >> >> > >> >> By default, if should_use_kmap() is not patched for arm64, it translates > >> >> to page_is_ram(); acpi_map() would simply use a kmap() which returns the > >> >> current kernel linear mapping on arm64. > >> > > >> > The problem with kmap() is that it only maps a single page. I've seen > >> > tables over 4k which is why I patched acpi_map() not to use kmap() on > >> > arm64. > >> > >> Right. Mark replied to this before I could; using kmap() enforced a 4k > >> (one page) limit that we kept breaking with some ACPI tables being larger > >> than that (DSDTs and SSDTs, fwiw). This would lead to some very odd behaviors > >> when most but not all of a device definition was within the page; using the > >> table checksums was one way of detecting the issues. > > > > OK. So I think Mark's original patch was ok, assuming that the System > > Memory cases mentioned by Graeme are detected with page_is_ram(). > > page_is_ram() returns whether a pfn is covered by the linear mapping, > so memory before the kernel or after a mem= limit will be > misidentified. OK. So in conclusion acpi_os_ioremap() may need to create a cacheable mapping even when !page_is_ram() but it has no way of knowing that unless we change the core ACPI code to differentiate between ioremap_cache and ioremap_nocache. Did I get it right? -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/