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

[Suzuki K. Poulose]

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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Signed-off-by: Suzuki K. Poulose <suzuki.poulose@xxxxxxx>
> > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> > ---
> >   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@xxxxxxx>

Thanks
Suzuki

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