Re: [PATCH] powerpc/Kconfig: limit the PPC_85xx DATA_SHIFT range to STRICT_KERNEL_RWX

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 11/10/2026 à 13:31, Julian Braha a écrit :
> On PPC_85xx, enabling DEBUG_PAGEALLOC without STRICT_KERNEL_RWX activates
> the DATA_SHIFT range of 20..24, but since the PAGE_SHIFT default is
> outside the range (12), kconfig adjusts it to 20, causing 1mb alignment
> instead of 4kb. However, the larger alignment is only needed for the
> separate kernel permissions provided by STRICT_KERNEL_RWX.
> 
> Since PPC_85xx uses page poisoning for DEBUG_PAGEALLOC and does not
> support KFENCE, let's restrict this range to STRICT_KERNEL_RWX.
> 
> This out-of-range default was detected by kconfirm, a static analysis tool
> for Kconfig.

Looks like with this change I'm now able to set DATA_SHIFT to any value 
when STRICT_KERNEL_RWX is not set and DEBUG_PAGEALLOC is set.

The range used to protect against that.

 > > Signed-off-by: Julian Braha <julianbraha@gmail.com>
> ---
>   arch/powerpc/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index c3b6cd655606..5e2a4799438d 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -896,7 +896,7 @@ config DATA_SHIFT
>   	default 24 if STRICT_KERNEL_RWX && PPC64
>   	range 17 28 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_BOOK3S_32
>   	range 14 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_8xx
> -	range 20 24 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_85xx
> +	range 20 24 if STRICT_KERNEL_RWX && PPC_85xx
>   	default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
>   	default 18 if (DEBUG_PAGEALLOC || KFENCE) && PPC_BOOK3S_32
>   	default 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_8xx && \