[U-Boot] [PATCH v2] arm64: booti: allow to place kernel image anywhere in physical memory

[Mark Rutland <mark.rutland@arm.com>]

On Wed, Mar 08, 2017 at 11:35:12AM +0900, Masahiro Yamada wrote:
> At first, the ARM64 Linux booting requirement recommended that the
> kernel image be placed text_offset bytes from 2MB aligned base near
> the start of usable system RAM because memory below that base address
> was unusable at that time.
> 
> This requirement was relaxed by Linux commit a7f8de168ace ("arm64:
> allow kernel Image to be loaded anywhere in physical memory").
> Since then, the bit 3 of the flags field indicates the tolerance
> of the kernel physical placement.  If this bit is set, the 2MB
> aligned base may be anywhere in physical memory.  For details, see
> Documentation/arm64/booting.txt of Linux.
> 
> The booti command should be also relaxed.  If the bit 3 is set,
> images->ep is respected, and the image is placed at the nearest
> bootable location.  Otherwise, it is relocated to the start of the
> system RAM to keep the original behavior.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
> Changes in v2:
>   - Use le64_to_cpu() for correct endian-ness
>   - Check the bit 3
> 
>  cmd/booti.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/cmd/booti.c b/cmd/booti.c
> index bff87a8..8f3507d 100644
> --- a/cmd/booti.c
> +++ b/cmd/booti.c
> @@ -11,6 +11,8 @@
>  #include <image.h>
>  #include <lmb.h>
>  #include <mapmem.h>
> +#include <linux/kernel.h>
> +#include <linux/sizes.h>
>  
>  DECLARE_GLOBAL_DATA_PTR;
>  
> @@ -20,7 +22,7 @@ struct Image_header {
>  	uint32_t	code1;		/* Executable code */
>  	uint64_t	text_offset;	/* Image load offset, LE */
>  	uint64_t	image_size;	/* Effective Image size, LE */
> -	uint64_t	res1;		/* reserved */
> +	uint64_t	flags;		/* Kernel flags, LE */
>  	uint64_t	res2;		/* reserved */
>  	uint64_t	res3;		/* reserved */
>  	uint64_t	res4;		/* reserved */
> @@ -51,10 +53,18 @@ static int booti_setup(bootm_headers_t *images)
>  	}
>  
>  	/*
> -	 * If we are not at the correct run-time location, set the new
> -	 * correct location and then move the image there.
> +	 * If bit 3 of the flags field is set, the 2MB aligned base of the
> +	 * kernel image can be anywhere in physical memory, so respect
> +	 * images->ep.  Otherwise, relocate the image to the base of RAM
> +	 * since memory below it is not accessible via the linear mapping.
>  	 */
> -	dst = gd->bd->bi_dram[0].start + le64_to_cpu(ih->text_offset);
> +	if (le64_to_cpu(ih->flags) & BIT(3))
> +		dst = images->ep - le64_to_cpu(ih->text_offset);

I take it this is a pre-correction for the ALIGN() below?

> +	else
> +		dst = gd->bd->bi_dram[0].start;
> +
> +	dst = ALIGN(dst, SZ_2M);
> +	dst += le64_to_cpu(ih->text_offset);

There's one last wrinkle to take care of here, if we want to boot a
kernel older than commit a2c1d73b94ed49f5 (i.e. v3.16). Until then, the
text_offset was of unknown endianness.

As mentiond in the Linux documentation, you can detect this based on the
image_size field, e.g.

	uint64_t text_offset;

	/*
	 * Prior to Linux commit a2c1d73b94ed49f5, the text_offset field
	 * is of unknown endianness. In these cases, the image_size
	 * field is zero, and we can assume a fixed value of 0x80000.
	 */
	if (le64_to_cpu(ih->image_size) == 0)
		text_offset = 0x80000;
	else
		text_offset = (le64_to_cpu(ih->text_offset));
		
... then you can reuse that text_offset value for both cases above.

Otherwise, this looks fine to me.

Thanks,
Mark.