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/[email protected]/#t > [0] > Cc: Catalin Marinas <[email protected]> > Cc: Will Deacon <[email protected]> > Cc: "James E.J. Bottomley" <[email protected]> > Cc: Helge Deller <[email protected]> > Cc: Madhavan Srinivasan <[email protected]> > Cc: Michael Ellerman <[email protected]> > Cc: Lorenzo Stoakes <[email protected]> > Cc: "Liam R. Howlett" <[email protected]> > Cc: Vlastimil Babka <[email protected]> > Cc: Mike Rapoport <[email protected]> > Cc: Suren Baghdasaryan <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: "Matthew Wilcox (Oracle)" <[email protected]> > Cc: Jan Kara <[email protected]> > Cc: Zi Yan <[email protected]> > Cc: Baolin Wang <[email protected]> > Cc: Nico Pache <[email protected]> > Cc: Ryan Roberts <[email protected]> > Cc: Dev Jain <[email protected]> > Cc: Barry Song <[email protected]> > Cc: Lance Yang <[email protected]> > Cc: Usama Arif <[email protected]> > Cc: Kevin Brodsky <[email protected]> > Cc: Muhammad Usama Anjum <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > > 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 >
