[PATCH 0/4] mm: Fix page-table teardown during memory hot-remove

[Muchun Song <songmuchun@bytedance.com>]

Memory hot-remove can free page tables allocated through different
paths. Some of these paths run page-table constructors, while others,
including generic sparse-vmemmap population, do not. The teardown
paths on x86, RISC-V and arm64 do not consistently handle this
distinction, leaving constructors and destructors unbalanced and
corrupting NR_PAGETABLE accounting.

On x86, the destructor is missing for vmemmap PTE tables allocated by
HugeTLB vmemmap optimization. RISC-V also misses the destructor for
constructed PUD tables. Conversely, arm64 and RISC-V can run
destructors on vmemmap tables that were never constructed.

This series uses PageTable() to determine whether a destructor is
needed before freeing a page-table page. The RISC-V fixes share a
common freeing helper across PTE, PMD and PUD teardown.

This series is limited to bug fixes for the existing teardown paths.
A follow-up series will convert runtime vmemmap page-table allocation
to the generic page-table allocation helpers, ensuring that these
tables run the corresponding constructors. Once these tables follow
the normal constructor and destructor lifecycle, the PageTable()
checks in the arm64 and RISC-V teardown paths can be removed.

Muchun Song (4):
  x86/mm: fix missing pgtable destructor for vmemmap tables
  riscv/mm: fix hotplug page-table destructor handling
  riscv/mm: fix missing destructor for hotplug PUD tables
  arm64/mm: fix destructor for unconstructed hotplug page tables

 arch/arm64/mm/mmu.c   |  3 ++-
 arch/riscv/mm/init.c  | 34 +++++++++++++++-------------------
 arch/x86/mm/init_64.c |  2 ++
 3 files changed, 19 insertions(+), 20 deletions(-)


base-commit: a92f009ac1c21986ff1ea0706419e545a4739513
-- 
2.54.0