Re: [PATCH RFC 06/35] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range_noprof()

David Hildenbrand
2025-10-09T06:12:40Z

On 09.10.25 06:21, Balbir Singh wrote:
> On 8/22/25 06:06, David Hildenbrand wrote:
>> Let's reject them early, which in turn makes folio_alloc_gigantic() reject
>> them properly.
>>
>> To avoid converting from order to nr_pages, let's just add MAX_FOLIO_ORDER
>> and calculate MAX_FOLIO_NR_PAGES based on that.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> include/linux/mm.h | 6 ++++--
>> mm/page_alloc.c | 5 ++++-
>> 2 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 00c8a54127d37..77737cbf2216a 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2055,11 +2055,13 @@ static inline long folio_nr_pages(const struct folio *folio)
>>
>> /* Only hugetlbfs can allocate folios larger than MAX_ORDER */
>> #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
>> -#define MAX_FOLIO_NR_PAGES (1UL << PUD_ORDER)
>> +#define MAX_FOLIO_ORDER PUD_ORDER
>
> Do we need to check for CONTIG_ALLOC as well with CONFIG_ARCH_HAS_GIGANTIC_PAGE?
>

I don't think so, can you elaborate?

>> #else
>> -#define MAX_FOLIO_NR_PAGES MAX_ORDER_NR_PAGES
>> +#define MAX_FOLIO_ORDER MAX_PAGE_ORDER
>> #endif
>>
>> +#define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER)
>> +
>> /*
>> * compound_nr() returns the number of pages in this potentially compound
>> * page. compound_nr() can be called on a tail page, and is defined to
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index ca9e6b9633f79..1e6ae4c395b30 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6833,6 +6833,7 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
>> int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>> acr_flags_t alloc_flags, gfp_t gfp_mask)
>> {
>> + const unsigned int order = ilog2(end - start);
>
> Do we need a VM_WARN_ON(end < start)?

I don't think so.

>
>> unsigned long outer_start, outer_end;
>> int ret = 0;
>>
>> @@ -6850,6 +6851,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>> PB_ISOLATE_MODE_CMA_ALLOC :
>> PB_ISOLATE_MODE_OTHER;
>>
>> + if (WARN_ON_ONCE((gfp_mask & __GFP_COMP) && order > MAX_FOLIO_ORDER))
>> + return -EINVAL;
>> +
>> gfp_mask = current_gfp_context(gfp_mask);
>> if (__alloc_contig_verify_gfp_mask(gfp_mask, (gfp_t *)&cc.gfp_mask))
>> return -EINVAL;
>> @@ -6947,7 +6951,6 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>> free_contig_range(end, outer_end - end);
>> } else if (start == outer_start && end == outer_end && is_power_of_2(end - start)) {
>> struct page *head = pfn_to_page(start);
>> - int order = ilog2(end - start);
>>
>> check_new_pages(head, order);
>> prep_new_page(head, order, gfp_mask, 0);
>
> Acked-by: Balbir Singh <balbirs@nvidia.com>

Thanks for the review, but note that this is already upstream.

--
Cheers

David / dhildenb