[PATCH] arm64: expose kernel page size in Image header flags
Ard Biesheuvel
ard.biesheuvel at linaro.org
Fri Sep 18 02:36:56 PDT 2015
On 18 September 2015 at 10:17, Suzuki K. Poulose <Suzuki.Poulose at arm.com> wrote:
> On 17/09/15 10:32, Ard Biesheuvel wrote:
>>
>> In order for a bootloader to be able to decide whether a certain
>> arm64 kernel image is compatible with the hardware it is running
>> on, it needs to be able to find out for which page size the kernel
>> was built. This is necessary, since the architecture does not
>> mandate support for all page sizes it defines, and the kernel cannot
>> boot to a state where it can print a diagnostic if it was built for
>> a page size that is not supported by the hardware.
>>
>> So assign two bits in the flags field of the Image header, and set
>> them according to the build time page size. For backward compatibility,
>> retain the 0b00 value as 'unspecified'.
>>
>> Acked-by: Catalin Marinas <catalin.marinas at arm.com>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>
>
> Ard,
>
> I picked this patch based on the our initial discussion on 16K page size
> series, and added it to the V2 of the series.
>
> https://lkml.org/lkml/2015/9/15/716
>
Ah, I missed that, sorry.
I don't care which version makes it eventually,
>
>
>> ---
>> Documentation/arm64/booting.txt | 3 ++-
>> arch/arm64/kernel/image.h | 4 +++-
>> 2 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/arm64/booting.txt
>> b/Documentation/arm64/booting.txt
>> index 1690350f16e7..46056e7d766e 100644
>> --- a/Documentation/arm64/booting.txt
>> +++ b/Documentation/arm64/booting.txt
>> @@ -104,7 +104,8 @@ Header notes:
>> - The flags field (introduced in v3.17) is a little-endian 64-bit field
>> composed as follows:
>> Bit 0: Kernel endianness. 1 if BE, 0 if LE.
>> - Bits 1-63: Reserved.
>> + Bits 1-2: Kernel page size. 0=unspecified, 1=4K, 2=16K, 3=64K
>> + Bits 3-63: Reserved.
>>
>> - When image_size is zero, a bootloader should attempt to keep as much
>> memory as possible free for use by the kernel immediately after the
>> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
>> index 8fae0756e175..5def289bda84 100644
>> --- a/arch/arm64/kernel/image.h
>> +++ b/arch/arm64/kernel/image.h
>> @@ -47,7 +47,9 @@
>> #define __HEAD_FLAG_BE 0
>> #endif
>>
>> -#define __HEAD_FLAGS (__HEAD_FLAG_BE << 0)
>> +#define __HEAD_FLAG_PAGE_SIZE ((PAGE_SHIFT - 10) / 2)
>> +
>> +#define __HEAD_FLAGS (__HEAD_FLAG_BE << 0) | (__HEAD_FLAG_PAGE_SIZE <<
>> 1)
>>
>
> FWIW,
>
> Tested-by: Suzuki K. Poulose <suzuki.poulose at arm.com>
>
Thank you,
Ard.
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