Re: [PATCH v2 0/6] mm: add basic PTE const type-safety

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 03/08/2026 à 18:43, Pedro Falcato a écrit :
> Since forever, MM code has thrown pte_t * around with no concern for const
> safety, or typesafety of any kind. This is confusing. Attempt to address it
> by:

What do you mean by "typesafety of any kind" ?

On powerpc64, pte_t is a struct so you can't play-up too much with it.

On powerpc32, pte_t is a long int because having it as a struct is 
counter-performant, but we have it as a struct when __CHECKER__ is 
defined, ie when doing a sparse check with 'make C=2'.


> 1) Making sure pte_get*() helpers can cope with const pte_t * arguments
> 2) Constifying the pte_offset_map_ro_nolock() return type, which by definition
> already pledges that users will not write to it.
> 
> These two simple steps were already able to uncover code smell from
> khugepaged + do_swap_page().
> 
> Separate steps could include introducing pte_offset_map_ro_lock() for more
> widespread usage of this.
> 
> Benefits of this include less confusion and better type-safety. It could also
> futurely aid in efforts such as [0] which may want semantic annotation of these
> accesses.
> 
> Based on mm-unstable and compile-tested on a handful of architectures.
> 
> No functional changes intended.
> 

For the series,

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>



> [CC list editorially trimmed for brevity reasons; apologies if you're not on it]
> 
> Link: https://lore.kernel.org/linux-mm/20260526-kpkeys-v8-0-eaaacdacc67c@arm.com/#t [0]
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Lorenzo Stoakes <ljs@kernel.org>
> Cc: "Liam R. Howlett" <liam@infradead.org>
> Cc: Vlastimil Babka <vbabka@kernel.org>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Nico Pache <npache@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Barry Song <baohua@kernel.org>
> Cc: Lance Yang <lance.yang@linux.dev>
> Cc: Usama Arif <usama.arif@linux.dev>
> Cc: Kevin Brodsky <kevin.brodsky@arm.com>
> Cc: Muhammad Usama Anjum <usama.anjum@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-parisc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-mm@kvack.org
> Cc: linux-fsdevel@vger.kernel.org
> 
> v2:
>   - Small fixups on the arm64 side
>   - Re-order patches in a way such that bisection is preserved
>   - Pick up Helge's patch dropping parisc ptep_get()
>   - Constify s390's ptep_get() as well
> 
> Helge Deller (1):
>    parisc: Drop own implementations for ptep_get() and
>      ptep_test_and_clear_young()
> 
> Pedro Falcato (5):
>    mm/arm64: constify pte_get*() and contpte get logic
>    mm/powerpc/8xx: constify ptep_get() argument
>    mm/s390: constify ptep_get() argument
>    mm: constify generic pte_get*()
>    mm: constify the pte_offset_map_ro_nolock() return value
> 
>   arch/arm64/include/asm/pgtable.h             | 10 +++++-----
>   arch/arm64/mm/contpte.c                      | 11 ++++++++---
>   arch/parisc/include/asm/pgtable.h            | 20 --------------------
>   arch/powerpc/include/asm/nohash/32/pte-8xx.h |  2 +-
>   arch/powerpc/mm/pgtable.c                    |  2 +-
>   arch/s390/include/asm/pgtable.h              |  2 +-
>   include/linux/mm.h                           |  4 ++--
>   include/linux/pgtable.h                      |  8 ++++----
>   mm/filemap.c                                 |  2 +-
>   mm/khugepaged.c                              |  2 +-
>   mm/pgtable-generic.c                         |  4 ++--
>   11 files changed, 26 insertions(+), 41 deletions(-)
>