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(-)
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:
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.
[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(-)
--
2.55.0
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(-) >
On Mon, Aug 03, 2026 at 05:43:54PM +0100, Pedro Falcato wrote: > 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: > 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. Even though the pte accesses should always be type-safe, this series does not really address the problem completely and instead changes things only for a small set of pte access sites. So just wondering how much beneficial this series really is ? > > [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(-) > > -- > 2.55.0 >
On Wed, Aug 05, 2026 at 04:12:21PM +0530, Anshuman Khandual wrote: > On Mon, Aug 03, 2026 at 05:43:54PM +0100, Pedro Falcato wrote: > > 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: > > 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. > > Even though the pte accesses should always be type-safe, this series does > not really address the problem completely and instead changes things only > for a small set of pte access sites. So just wondering how much beneficial > this series really is ? This series is meant to be a small step in the right direction (while feeling out what the community thinks, which seems to be receptive). The obvious next steps would be to introduce some sort of const pte_t *pte_offset_map_ro_lock(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, spinlock_t **ptlp); and use it in more places. That will obviously involve a bit of churn. -- Pedro
On 03/08/2026 5:43 pm, Pedro Falcato wrote: > 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: > 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. I've reviewed the entire series. Hence: Reviewed-by: Muhammad Usama Anjum <usama.anjum@arm.com> > > [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(-) > -- Thanks, Usama
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