linux-kernel - Re: [PATCH mm-hotfixes-unstable] mm: Pass page directly instead of using folio

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Message-ID: <0de8d37e-5977-43f4-8e21-0ad47130d62f@redhat.com>
Date: Wed, 6 Aug 2025 22:21:27 +0200
From: David Hildenbrand <david@...hat.com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org
Cc: ryan.roberts@....com, willy@...radead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, catalin.marinas@....com, will@...nel.org,
 Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
 jannh@...gle.com, anshuman.khandual@....com, peterx@...hat.com,
 joey.gouly@....com, ioworker0@...il.com, baohua@...nel.org,
 kevin.brodsky@....com, quic_zhenhuah@...cinc.com,
 christophe.leroy@...roup.eu, yangyicong@...ilicon.com,
 linux-arm-kernel@...ts.infradead.org, hughd@...gle.com,
 yang@...amperecomputing.com, ziy@...dia.com,
 syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
Subject: Re: [PATCH mm-hotfixes-unstable] mm: Pass page directly instead of
 using folio_page

On 06.08.25 16:56, Dev Jain wrote:
> In commit_anon_folio_batch(), we iterate over all pages pointed to by the
> PTE batch. Therefore we need to know the first page of the batch;
> currently we derive that via folio_page(folio, 0), but, that takes us
> to the first (head) page of the folio instead - our PTE batch may lie
> in the middle of the folio, leading to incorrectness.
> 
> Bite the bullet and throw away the micro-optimization of reusing the
> folio in favour of code simplicity.

Huh? We are still reusing the folio. There is a single 
vm_normal_page()+page_folio() lookup in that code.

Maybe what you meant is "Simplify the code by moving the folio lookup 
out of prot_numa_skip() such that we only have a single page+folio lookup."

> Derive the page and the folio in
> change_pte_range, and pass the page too to commit_anon_folio_batch to
> fix the aforementioned issue.
> 
> Reported-by: syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
> Fixes: cac1db8c3aad ("mm: optimize mprotect() by PTE batching")

Fell free to add a

Debugged-by: David Hildenbrand <david@...hat.com>

> Signed-off-by: Dev Jain <dev.jain@....com>

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb