linux-kernel - Re: [PATCH v1 10/36] mm: sanity-check maximum folio size in folio_set

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Message-ID: <f0c6e9f6-df09-4b10-9338-7bfe4aa46601@lucifer.local>
Date: Thu, 28 Aug 2025 16:00:31 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v1 10/36] mm: sanity-check maximum folio size in
 folio_set_order()

On Thu, Aug 28, 2025 at 12:01:14AM +0200, David Hildenbrand wrote:
> Let's sanity-check in folio_set_order() whether we would be trying to
> create a folio with an order that would make it exceed MAX_FOLIO_ORDER.
>
> This will enable the check whenever a folio/compound page is initialized
> through prepare_compound_head() / prepare_compound_page().

NIT: with CONFIG_DEBUG_VM set :)

>
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

LGTM (apart from nit below), so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/internal.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 45da9ff5694f6..9b0129531d004 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -755,6 +755,7 @@ static inline void folio_set_order(struct folio *folio, unsigned int order)
>  {
>  	if (WARN_ON_ONCE(!order || !folio_test_large(folio)))
>  		return;
> +	VM_WARN_ON_ONCE(order > MAX_FOLIO_ORDER);

Given we have 'full-fat' WARN_ON*()'s above, maybe worth making this one too?

>
>  	folio->_flags_1 = (folio->_flags_1 & ~0xffUL) | order;
>  #ifdef NR_PAGES_IN_LARGE_FOLIO
> --
> 2.50.1
>