linux-kernel - Re: [PATCHv3 09/11] arm64: Add page size to the kernel image header

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Date:	Thu, 15 Oct 2015 10:19:13 +0100
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	catalin.marinas@....com, will.deacon@....com,
	steve.capper@...aro.org, marc.zyngier@....com,
	ard.biesheuvel@...aro.org, christoffer.dall@...aro.org
Subject: Re: [PATCHv3 09/11] arm64: Add page size to the kernel image header

On 14/10/15 18:27, Mark Rutland wrote:
> On Wed, Oct 14, 2015 at 12:20:32PM +0100, Suzuki K. Poulose wrote:
>> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>>
>> This patch adds the page size to the arm64 kernel image header
>> so that one can infer the PAGESIZE used by the kernel. This will
>> be helpful to diagnose failures to boot the kernel with page size
>> not supported by the CPU.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
>> Acked-by: Catalin Marinas <catalin.marinas@....com>
>> Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
>> ---
>>   Documentation/arm64/booting.txt |    7 ++++++-
>>   arch/arm64/kernel/image.h       |    5 ++++-
>>   2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
>> index 7d9d3c2..aaf6d77 100644
>> --- a/Documentation/arm64/booting.txt
>> +++ b/Documentation/arm64/booting.txt
>> @@ -104,7 +104,12 @@ 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.
>> +  Bit 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 6eb8fee..e45759e 100644
>> --- a/arch/arm64/kernel/image.h
>> +++ b/arch/arm64/kernel/image.h
>> @@ -47,7 +47,10 @@
>>   #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)
>
> I'd prefer that we also had brackets around the whole of the
> __HEAD_FLAGS value, so we don't get caught out later on by some
> unexpected expansion (though we are safe currently).
>

Sure, will add that.

> With that:
>
> Acked-by: Mark Rutland <mark.rutland@....com>

Thanks
Suzuki

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