Re: powerpc/e500: WARNING: at mm/hugetlb.c:4755 hugetlb_add_hstate

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 10/11/2025 à 12:27, David Hildenbrand (Red Hat) a écrit :
> Thanks for the review!
> 
>>
>> So I think what you want instead is:
>>
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype
>> b/arch/powerpc/platforms/Kconfig.cputype
>> index 7b527d18aa5ee..1f5a1e587740c 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>> @@ -276,6 +276,7 @@ config PPC_E500
>>           select FSL_EMB_PERFMON
>>           bool
>>           select ARCH_SUPPORTS_HUGETLBFS if PHYS_64BIT || PPC64
>> +       select ARCH_HAS_GIGANTIC_PAGE if ARCH_SUPPORTS_HUGETLBFS
>>           select PPC_SMP_MUXED_IPI
>>           select PPC_DOORBELL
>>           select PPC_KUEP
>>
>>
>>
>>>        select ARCH_HAS_KCOV
>>>        select ARCH_HAS_KERNEL_FPU_SUPPORT    if PPC64 && PPC_FPU
>>>        select ARCH_HAS_MEMBARRIER_CALLBACKS
>>> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/
>>> platforms/Kconfig.cputype
>>> index 7b527d18aa5ee..4c321a8ea8965 100644
>>> --- a/arch/powerpc/platforms/Kconfig.cputype
>>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>>> @@ -423,7 +423,6 @@ config PPC_64S_HASH_MMU
>>>    config PPC_RADIX_MMU
>>>        bool "Radix MMU Support"
>>>        depends on PPC_BOOK3S_64
>>> -    select ARCH_HAS_GIGANTIC_PAGE
>>
>> Should remain I think.
>>
>>>        default y
>>>        help
>>>          Enable support for the Power ISA 3.0 Radix style MMU. Currently
> 
> 
> We also have PPC_8xx do a
> 
>      select ARCH_SUPPORTS_HUGETLBFS
> 
> And of course !PPC_RADIX_MMU (e.g., PPC_64S_HASH_MMU) through 
> PPC_BOOK3S_64.
> 
> Are we sure they cannot end up with gigantic folios through hugetlb?
> 

Yes indeed. My PPC_8xx is OK because I set CONFIG_ARCH_FORCE_MAX_ORDER=9 
(largest hugepage is 8M) but I do get the warning with the default value 
which is 8 (with 16k pages).

For PPC_64S_HASH_MMU, max page size is 16M, we get no warning with 
CONFIG_ARCH_FORCE_MAX_ORDER=8 which is the default value but get the 
warning with CONFIG_ARCH_FORCE_MAX_ORDER=7

Should CONFIG_ARCH_HAS_GIGANTIC_PAGE be set unconditionaly as soon as 
hugepages are selected, or should it depend on 
CONFIG_ARCH_FORCE_MAX_ORDER ? What is the cost of selecting 
CONFIG_ARCH_HAS_GIGANTIC_PAGE ?

Christophe