From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756882AbbEVKeX (ORCPT ); Fri, 22 May 2015 06:34:23 -0400 Received: from foss.arm.com ([217.140.101.70]:43360 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755960AbbEVKeV (ORCPT ); Fri, 22 May 2015 06:34:21 -0400 Date: Fri, 22 May 2015 11:34:17 +0100 From: Catalin Marinas To: Ard Biesheuvel Cc: Matt Fleming , Will Deacon , "linux-kernel@vger.kernel.org" , Hanjun Guo , Mark Salter , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] arm64: support ACPI tables outside of kernel RAM Message-ID: <20150522103417.GT29424@e104818-lin.cambridge.arm.com> References: <1431613373-10928-1-git-send-email-msalter@redhat.com> <20150518111143.GC21251@e104818-lin.cambridge.arm.com> <1431957525.9933.4.camel@deneb.redhat.com> <20150518164108.GH21251@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 On Mon, May 18, 2015 at 06:49:28PM +0200, Ard Biesheuvel wrote: > On 18 May 2015 at 18:41, Catalin Marinas wrote: > > On Mon, May 18, 2015 at 09:58:45AM -0400, Mark Salter wrote: > >> 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). > > > > OK, I had the impression that we could get away with this. > > > >> > > 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. > > > > Yes, please. > > > >> > 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. > > > > Do we have a guarantee that UEFI tells the kernel about the whole RAM? > > Yes, the UEFI memory map must describe all of RAM, no matter how it is > used. I may also describe some MMIO regions, but typically only > regions that it needs itself to implement the UEFI Runtime Services > (e.g., RTC base address, NOR flash for the variable store) > > So we could potentially query the UEFI memory map directly to find out > whether some otherwise unqualified region is backed by RAM or not, > although I'd prefer some intermediate data structure (such as the > physmem memblock table) if we go that route. OK, so my preferred options, in this order: 1. Change the core ACPI kernel code to distinguish between mapping I/O or RAM (could be as simple as acpi_map not using acpi_os_ioremap but another API). I guess the code knows when it plans to map tables or I/O registers 2. If the above is not possible, add the extra checks as per Mark's patch but I would rather call this resource "UEFI RAM" than "ACPI", it's not really ACPI specific. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Fri, 22 May 2015 11:34:17 +0100 Subject: [PATCH] arm64: support ACPI tables outside of kernel RAM In-Reply-To: References: <1431613373-10928-1-git-send-email-msalter@redhat.com> <20150518111143.GC21251@e104818-lin.cambridge.arm.com> <1431957525.9933.4.camel@deneb.redhat.com> <20150518164108.GH21251@e104818-lin.cambridge.arm.com> Message-ID: <20150522103417.GT29424@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, May 18, 2015 at 06:49:28PM +0200, Ard Biesheuvel wrote: > On 18 May 2015 at 18:41, Catalin Marinas wrote: > > On Mon, May 18, 2015 at 09:58:45AM -0400, Mark Salter wrote: > >> 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). > > > > OK, I had the impression that we could get away with this. > > > >> > > 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. > > > > Yes, please. > > > >> > 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. > > > > Do we have a guarantee that UEFI tells the kernel about the whole RAM? > > Yes, the UEFI memory map must describe all of RAM, no matter how it is > used. I may also describe some MMIO regions, but typically only > regions that it needs itself to implement the UEFI Runtime Services > (e.g., RTC base address, NOR flash for the variable store) > > So we could potentially query the UEFI memory map directly to find out > whether some otherwise unqualified region is backed by RAM or not, > although I'd prefer some intermediate data structure (such as the > physmem memblock table) if we go that route. OK, so my preferred options, in this order: 1. Change the core ACPI kernel code to distinguish between mapping I/O or RAM (could be as simple as acpi_map not using acpi_os_ioremap but another API). I guess the code knows when it plans to map tables or I/O registers 2. If the above is not possible, add the extra checks as per Mark's patch but I would rather call this resource "UEFI RAM" than "ACPI", it's not really ACPI specific. -- Catalin