mm: call ctor/dtor for kernel PTEs Since [1], constructors/destructors are expected to be called for all page table pages, at all levels and for both user and kernel pgtables. There is however one glaring exception: kernel PTEs are managed via separate helpers (pte_alloc_kernel/pte_free_kernel), which do not call the [cd]tor, at least not in the generic implementation. The most obvious reason for this anomaly is that init_mm is special-cased not to use split page table locks. As a result calling ptlock_init() for PTEs associated with init_mm would be wasteful, potentially resulting in dynamic memory allocation. However, pgtable [cd]tors perform other actions - currently related to accounting/statistics, and potentially more functionally significant in the future. Now that pagetable_pte_ctor() is passed the associated mm, we can make it skip the call to ptlock_init() for init_mm; this allows us to call the ctor from pte_alloc_one_kernel() too. This is matched by a call to the pgtable destructor in pte_free_kernel(); no special-casing is needed on that path, as ptlock_free() is already called unconditionally. (ptlock_free() is a no-op unless a ptlock was allocated for the given PTP.) This patch ensures that all architectures that rely on call the [cd]tor for kernel PTEs. pte_free_kernel() cannot be overridden so changing the generic implementation is sufficient. pte_alloc_one_kernel() can be overridden using __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, and a few architectures implement it by calling the page allocator directly. We amend those so that they call the generic __pte_alloc_one_kernel() instead, if possible, ensuring that the ctor is called. A few architectures do not use ; those will be taken care of separately. [1] https://lore.kernel.org/linux-mm/20250103184415.2744423-1-kevin.brodsky@arm.com/ Link: https://lkml.kernel.org/r/20250408095222.860601-4-kevin.brodsky@arm.com Signed-off-by: Kevin Brodsky Reviewed-by: Alexander Gordeev # s390 Cc: Albert Ou Cc: Andreas Larsson Cc: Catalin Marinas Cc: David S. Miller Cc: Geert Uytterhoeven Cc: Linus Waleij Cc: Madhavan Srinivasan Cc: Mark Rutland Cc: Matthew Wilcox (Oracle) Cc: Michael Ellerman Cc: Mike Rapoport Cc: Palmer Dabbelt Cc: Paul Walmsley Cc: Peter Zijlstra Cc: Qi Zheng Cc: Ryan Roberts Cc: Will Deacon Cc: Cc: Yang Shi Cc: Dave Hansen Signed-off-by: Andrew Morton