linux-kernel - Re: [PATCH RFC 06/35] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range

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Message-ID: <fa2e262c-d732-48e3-9c59-6ed7c684572c@nvidia.com>
Date: Thu, 9 Oct 2025 15:21:07 +1100
From: Balbir Singh <balbirs@...dia.com>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: 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,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 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,
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 Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
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 Vlastimil Babka <vbabka@...e.cz>, wireguard@...ts.zx2c4.com, x86@...nel.org,
 Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH RFC 06/35] mm/page_alloc: reject unreasonable
 folio/compound page sizes in alloc_contig_range_noprof()

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@...hat.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?

>  #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)?

>  	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@...dia.com>

Balbir