Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932545AbbEVNtj (ORCPT ); Fri, 22 May 2015 09:49:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53872 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932514AbbEVNtg (ORCPT ); Fri, 22 May 2015 09:49:36 -0400 Message-ID: <1432302546.9933.82.camel@deneb.redhat.com> Subject: Re: [PATCH] arm64: support ACPI tables outside of kernel RAM From: Mark Salter To: Catalin Marinas Cc: Ard Biesheuvel , Matt Fleming , Will Deacon , "linux-kernel@vger.kernel.org" , Hanjun Guo , "linux-arm-kernel@lists.infradead.org" Date: Fri, 22 May 2015 09:49:06 -0400 In-Reply-To: <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> <20150522103417.GT29424@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 Content-Length: 4358 Lines: 85 On Fri, 2015-05-22 at 11:34 +0100, Catalin Marinas wrote: > 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 >From my reading of the code, ACPI distinguishes a number of different address spaces and allows for the installation of handlers to access those various spaces. The problem with ACPI_ADR_SPACE_SYSTEM_MEMORY is that it covers both mmio and RAM and ACPI code makes no distinction between the two. x86 code uses page_is_ram() to decide whether to use kmap() or ioremap(). ia64 always uses ioremap() which sorts out the caching internally. For arm64, we ended up with using page_is_ram() to decide between ioremap_cache() an ioremap(). I don't think generic ACPI code has the ability to do any better than that. It really is an architecture decision based on address space attributes which ACPI doesn't know about. > > 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. > -- 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/