linux-kernel - Re: [PATCH v3.1 0/4] arm64: kexec,kdump: fix boot failures on acpi-only system

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Date:   Fri, 13 Jul 2018 07:49:45 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Baicar, Tyler" <tbaicar@...eaurora.org>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        James Morse <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>,
        Al Stone <al.stone@...aro.org>,
        Graeme Gregory <graeme.gregory@...aro.org>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH v3.1 0/4] arm64: kexec,kdump: fix boot failures on
 acpi-only system

On 13 July 2018 at 02:34, AKASHI Takahiro <takahiro.akashi@...aro.org> wrote:
> On Thu, Jul 12, 2018 at 05:49:19PM +0100, Will Deacon wrote:
>> Hi Akashi,
>>
>> On Tue, Jul 10, 2018 at 08:42:25AM +0900, AKASHI Takahiro wrote:
>> > This patch series is a set of bug fixes to address kexec/kdump
>> > failures which are sometimes observed on ACPI-only system and reported
>> > in LAK-ML before.
>>
>> I tried picking this up, along with Ard's fixup, but I'm seeing a build
>> failure for allmodconfig:
>>
>> arch/arm64/kernel/acpi.o: In function `__acpi_get_mem_attribute':
>> acpi.c:(.text+0x60): undefined reference to `efi_mem_attributes'
>>
>> I didn't investigate further. Please can you fix this?
>
> Because CONFIG_ACPI is on and CONFIG_EFI is off.
>
> This can happen in allmodconfig as CONFIG_EFI depends on
> !CONFIG_CPU_BIG_ENDIAN, which is actually on in this case.
>

Allowing both CONFIG_ACPI and CONFIG_CPU_BIG_ENDIAN to be configured
makes no sense at all. Things will surely break if you start using BE
memory accesses while parsing ACPI tables.

Allowing CONFIG_ACPI without CONFIG_EFI makes no sense either, since
on arm64, the only way to find the ACPI tables is through a UEFI
configuration table.

> Looking at __acpi_get_mem_attributes(), since there is no information
> available on memory attributes, what we can do at best is
>   * return PAGE_KERNEL (= cacheable) for mapped memory,
>   * return DEVICE_nGnRnE (= non-cacheable) otherwise
> (See a hunk to be applied on top of my patch#4.)
>
> I think that, after applying, acpi_os_ioremap() would work almost
> in the same way as the original before my patchset given that
> MAP memblock attribute is used only under CONFIG_EFI for now.
>
> Make sense?
>

Let's keep your code as is but fix the Kconfig dependencies instead.