Hi Chen,

On Sat, 2021-01-30 at 15:10 +0800, Chen Zhou wrote:
> Introduce macro CRASH_ALIGN for alignment, macro CRASH_ADDR_LOW_MAX
> for upper bound of low crash memory, macro CRASH_ADDR_HIGH_MAX for
> upper bound of high crash memory, use macroes instead.
> 
> Besides, keep consistent with x86, use CRASH_ALIGN as the lower bound
> of crash kernel reservation.
> 
> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
> Tested-by: John Donnelly <John.p.donnelly@oracle.com>
> ---
>  arch/arm64/include/asm/kexec.h | 6 ++++++
>  arch/arm64/mm/init.c           | 6 +++---
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index d24b527e8c00..3f6ecae0bc68 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -25,6 +25,12 @@
>  
> 
>  #define KEXEC_ARCH KEXEC_ARCH_AARCH64
>  
> 
> +/* 2M alignment for crash kernel regions */
> +#define CRASH_ALIGN	SZ_2M
> +
> +#define CRASH_ADDR_LOW_MAX	arm64_dma_phys_limit

I wonder if you could use 'ARCH_LOW_ADDRESS_LIMIT', instead of creating a new
define.

> +#define CRASH_ADDR_HIGH_MAX	MEMBLOCK_ALLOC_ACCESSIBLE
> +
>  #ifndef __ASSEMBLY__
>  
> 
>  /**
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 709d98fea90c..912f64f505f7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -84,8 +84,8 @@ static void __init reserve_crashkernel(void)
>  
> 
>  	if (crash_base == 0) {
>  		/* Current arm64 boot protocol requires 2MB alignment */
> -		crash_base = memblock_find_in_range(0, arm64_dma_phys_limit,
> -				crash_size, SZ_2M);
> +		crash_base = memblock_find_in_range(CRASH_ALIGN, CRASH_ADDR_LOW_MAX,
> +				crash_size, CRASH_ALIGN);

Actually we could get rid of CRASH_ADDR_LOW_MAX altogether if we used
memblock_alloc_low() here (modulo the slight refactoring needed to accommodate
it).

Regards,
Nicolas