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

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

[Ard Biesheuvel]

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@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 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)
 
 /*
  * These will output as part of the Image header, which should be little-endian
-- 
1.9.1

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

[Mark Rutland]

On Thu, Sep 17, 2015 at 10:32:25AM +0100, 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@arm.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

This looks sane to me.

FWIW: Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

> ---
>  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)
>  
>  /*
>   * These will output as part of the Image header, which should be little-endian
> -- 
> 1.9.1
> 

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

[Suzuki K. Poulose]

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@arm.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@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


> ---
>   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@arm.com>


Thanks
Suzuki

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

[Ard Biesheuvel]

On 18 September 2015 at 10:17, Suzuki K. Poulose <Suzuki.Poulose@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@arm.com>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@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@arm.com>
>

Thank you,
Ard.