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

[Ritesh Harjani (IBM)]

Christophe Leroy <christophe.leroy at csgroup.eu> writes:

> 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
>

This made me thinking.. Currently we can also get warning even on
book3s64 when CONFIG_PPC_RADIX_MMU=n is selected because max page size
in case of HASH can be 16G. I guess this was not getting tested in
regular CI because it requires us to disable RADIX config during build.

We will end up in this path on Hash where MAX_PAGE_ORDER is
CONFIG_ARCH_FORCE_MAX_ORDER which is 8, this is because we HAVE
ARCH_HAS_GIGANTIC_PAGE=n in case of only HASH.