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

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

Le 14/10/2026 à 13:23, Julian Braha a écrit :
> On 10/12/26 11:28, Christophe Leroy (CS GROUP) wrote:
>> 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.
> 
> Sorry, yeah kconfig can be tricky...
> 
>> +    range 20 24 if STRICT_KERNEL_RWX && PPC_85xx
> I think if we keep this ^ and then add another range:
> 
>      range PAGE_SHIFT 24 if !STRICT_KERNEL_RWX && PPC_85xx
> 
> this would cover your STRICT_KERNEL_RWX=n and DEBUG_PAGEALLOC=y
> configuration while resolving the 12 -> 20

Yes I think that should work.

Christophe