From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753598AbbERN7Y (ORCPT ); Mon, 18 May 2015 09:59:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41289 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751532AbbERN7R (ORCPT ); Mon, 18 May 2015 09:59:17 -0400 Message-ID: <1431957525.9933.4.camel@deneb.redhat.com> Subject: Re: [PATCH] arm64: support ACPI tables outside of kernel RAM From: Mark Salter To: Catalin Marinas Cc: Will Deacon , Matt Fleming , Ard Biesheuvel , linux-kernel@vger.kernel.org, Hanjun Guo , linux-arm-kernel@lists.infradead.org Date: Mon, 18 May 2015 09:58:45 -0400 In-Reply-To: <20150518111143.GC21251@e104818-lin.cambridge.arm.com> References: <1431613373-10928-1-git-send-email-msalter@redhat.com> <20150518111143.GC21251@e104818-lin.cambridge.arm.com> Organization: Red Hat, Inc Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2015-05-18 at 12:11 +0100, Catalin Marinas wrote: > On Thu, May 14, 2015 at 10:22:53AM -0400, Mark Salter wrote: > > There is no guarantee that ACPI tables will be located in RAM linearly > > mapped by the kernel. This could be because UEFI placed them below the > > kernel image or because mem= places them beyond the reach of the linear > > kernel mapping. Even though these tables are outside the linear mapped > > RAM, they still need to be accessed as normal memory in order to support > > unaligned accesses from ACPI code. In this case, the page_is_ram() test > > in acpi_os_ioremap() is not sufficient. > > And can we not simply add the rest of the RAM to the resource list as > "System RAM" without being part of memblock? If it is in "System RAM", then it needs a valid pfn and struct page. Parts of the kernel expect that (page_is_ram(), memory hotplug, etc). > > > Additionally, if the table spans multiple pages, it may fall partially > > within the linear map and partially without. If the table overlaps the > > end of the linear map, the test for whether or not to use the existing > > mapping in ioremap_cache() could lead to a panic when ACPI code tries > > to access the part beyond the end of the linear map. This patch > > attempts to address these problems. > > That's a problem with ioremap_cache() that should be fixed independently. I can submit that separately if you prefer. > > Ideally, I'd like to see the ACPI code use different APIs to distinguish > between table access in RAM and device access, so that we don't have to > guess whether the page is RAM or not. > I don't think the ACPI code has enough info to make that decision, but I'm not sure honestly. From mboxrd@z Thu Jan 1 00:00:00 1970 From: msalter@redhat.com (Mark Salter) Date: Mon, 18 May 2015 09:58:45 -0400 Subject: [PATCH] arm64: support ACPI tables outside of kernel RAM In-Reply-To: <20150518111143.GC21251@e104818-lin.cambridge.arm.com> References: <1431613373-10928-1-git-send-email-msalter@redhat.com> <20150518111143.GC21251@e104818-lin.cambridge.arm.com> Message-ID: <1431957525.9933.4.camel@deneb.redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 2015-05-18 at 12:11 +0100, Catalin Marinas wrote: > On Thu, May 14, 2015 at 10:22:53AM -0400, Mark Salter wrote: > > There is no guarantee that ACPI tables will be located in RAM linearly > > mapped by the kernel. This could be because UEFI placed them below the > > kernel image or because mem= places them beyond the reach of the linear > > kernel mapping. Even though these tables are outside the linear mapped > > RAM, they still need to be accessed as normal memory in order to support > > unaligned accesses from ACPI code. In this case, the page_is_ram() test > > in acpi_os_ioremap() is not sufficient. > > And can we not simply add the rest of the RAM to the resource list as > "System RAM" without being part of memblock? If it is in "System RAM", then it needs a valid pfn and struct page. Parts of the kernel expect that (page_is_ram(), memory hotplug, etc). > > > Additionally, if the table spans multiple pages, it may fall partially > > within the linear map and partially without. If the table overlaps the > > end of the linear map, the test for whether or not to use the existing > > mapping in ioremap_cache() could lead to a panic when ACPI code tries > > to access the part beyond the end of the linear map. This patch > > attempts to address these problems. > > That's a problem with ioremap_cache() that should be fixed independently. I can submit that separately if you prefer. > > Ideally, I'd like to see the ACPI code use different APIs to distinguish > between table access in RAM and device access, so that we don't have to > guess whether the page is RAM or not. > I don't think the ACPI code has enough info to make that decision, but I'm not sure honestly.