linux-kernel - Re: [PATCH 09/15] arm64: Add page size to the kernel image header

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Date:	Sat, 10 Oct 2015 19:22:03 +0200
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
	ard.biesheuvel@...aro.org, Marc.Zyngier@....com,
	Catalin.Marinas@....com, Will.Deacon@....com,
	linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH 09/15] arm64: Add page size to the kernel image header

On Tue, Sep 15, 2015 at 04:41:18PM +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>
> ---
>  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 8fae075..73b736c 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)
>  
>  /*
>   * These will output as part of the Image header, which should be little-endian
> -- 
> 1.7.9.5
> 

Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
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