linux-kernel - Re: [PATCH v1 06/36] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range

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Message-ID: <6a2e2ba2-e5ea-4744-a66e-790216c1e762@redhat.com>
Date: Fri, 29 Aug 2025 11:58:49 +0200
From: David Hildenbrand <david@...hat.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>,
 SeongJae Park <sj@...nel.org>, Alexander Potapenko <glider@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Brendan Jackman <jackmanb@...gle.com>, Christoph Lameter <cl@...two.org>,
 Dennis Zhou <dennis@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>,
 dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
 iommu@...ts.linux.dev, io-uring@...r.kernel.org,
 Jason Gunthorpe <jgg@...dia.com>, Jens Axboe <axboe@...nel.dk>,
 Johannes Weiner <hannes@...xchg.org>, John Hubbard <jhubbard@...dia.com>,
 kasan-dev@...glegroups.com, kvm@...r.kernel.org,
 Linus Torvalds <torvalds@...ux-foundation.org>, linux-arm-kernel@...s.com,
 linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
 linux-ide@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-mips@...r.kernel.org, linux-mmc@...r.kernel.org, linux-mm@...ck.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-scsi@...r.kernel.org, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
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 Vlastimil Babka <vbabka@...e.cz>, wireguard@...ts.zx2c4.com, x86@...nel.org
Subject: Re: [PATCH v1 06/36] mm/page_alloc: reject unreasonable
 folio/compound page sizes in alloc_contig_range_noprof()

On 29.08.25 02:33, Liam R. Howlett wrote:
> * David Hildenbrand <david@...hat.com> [250827 18:04]:
>> 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.
>>
>> Reviewed-by: Zi Yan <ziy@...dia.com>
>> Acked-by: SeongJae Park <sj@...nel.org>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> Nit below, but..
> 
> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.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
>>   #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 baead29b3e67b..426bc404b80cc 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);
>>   	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);
> 
> You have changed this from an int to a const unsigned int, which is
> totally fine but it was left out of the change log.  

Considered to trivial to document, but I can add a sentence about that.

> Probably not really
> worth mentioning but curious why the change to unsigned here?

orders are always unsigned, like folio_order().

Thanks!

-- 
Cheers

David / dhildenb