[PATCH] arm64: expose kernel page size in Image header flags

[Ard Biesheuvel]

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.