Re: [PATCH 12/14] arm64: Check for selected granule support

From: Catalin Marinas
Date: Fri Sep 04 2015 - 09:58:28 EST


On Wed, Sep 02, 2015 at 12:19:07PM +0200, Ard Biesheuvel wrote:
> On 2 September 2015 at 11:48, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> > Couldn't we allocate some flag bits in the Image header to communicate
> > the page size to the bootloader?
>
> Something like this perhaps?
>
> ------------8<---------------
> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
> index 7d9d3c2286b2..13a8aaa9a6e9 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)

I'm fine with this.

--
Catalin
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