Re: (bisected) [PATCH v2 08/37] mm/hugetlb: check for unreasonable folio sizes when registering hstate

David Hildenbrand
2025-10-09T07:22:24Z

On 09.10.25 09:14, Christophe Leroy wrote:
> Hi David,
>
> Le 01/09/2025 à 17:03, David Hildenbrand a écrit :
>> Let's check that no hstate that corresponds to an unreasonable folio size
>> is registered by an architecture. If we were to succeed registering, we
>> could later try allocating an unsupported gigantic folio size.
>>
>> Further, let's add a BUILD_BUG_ON() for checking that HUGETLB_PAGE_ORDER
>> is sane at build time. As HUGETLB_PAGE_ORDER is dynamic on powerpc, we have
>> to use a BUILD_BUG_ON_INVALID() to make it compile.
>>
>> No existing kernel configuration should be able to trigger this check:
>> either SPARSEMEM without SPARSEMEM_VMEMMAP cannot be configured or
>> gigantic folios will not exceed a memory section (the case on sparse).
>>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>
> I get following warning on powerpc with linus tree, bisected to commit
> 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes when
> registering hstate")

Do you have the kernel config around? Is it 32bit?

That would be helpful.

[...]

>> ---
>> mm/hugetlb.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 1e777cc51ad04..d3542e92a712e 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -4657,6 +4657,7 @@ static int __init hugetlb_init(void)
>>
>> BUILD_BUG_ON(sizeof_field(struct page, private) * BITS_PER_BYTE <
>> __NR_HPAGEFLAGS);
>> + BUILD_BUG_ON_INVALID(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER);
>>
>> if (!hugepages_supported()) {
>> if (hugetlb_max_hstate || default_hstate_max_huge_pages)
>> @@ -4740,6 +4741,7 @@ void __init hugetlb_add_hstate(unsigned int order)
>> }
>> BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
>> BUG_ON(order < order_base_2(__NR_USED_SUBPAGE));
>> + WARN_ON(order > MAX_FOLIO_ORDER);
>> h = &hstates[hugetlb_max_hstate++];
>> __mutex_init(&h->resize_lock, "resize mutex", &h->resize_key);
>> h->order = order;

We end up registering hugetlb folios that are bigger than
MAX_FOLIO_ORDER. So we have to figure out how a config can trigger that
(and if we have to support that).

--
Cheers

David / dhildenb