[PATCH v2 0/4] mm: Fix page-table teardown during memory hot-remove

[Muchun Song <songmuchun@bytedance.com>]

Memory hot-remove can free page-table pages allocated through paths with
different constructor state. Some paths run the page-table constructor,
while generic sparse-vmemmap population may not. The x86, RISC-V, and
arm64 teardown paths did not handle that distinction consistently,
leaving constructor/destructor accounting unbalanced.

Make pagetable_free() test PageTable() and run the destructor only when
the constructor initialized the page. The RISC-V and arm64 fixes then
use this common helper for their memory-hot-remove paths.

The architecture fixes depend on the common MM change in patch 1, so
this remains a single series. I expect it to go through the MM tree,
with review or acks from the relevant architecture maintainers.

Changes since v1:
- Move the destructor decision from x86 into pagetable_free(), as
  suggested by David Hildenbrand.
- Use pagetable_free() for non-reserved RISC-V page-table pages and
  simplify reserved-page handling.
- Collect David Hildenbrand's Acked-by on the RISC-V PUD fix.
- Use pagetable_free() for arm64 intermediate page-table pages, as
  suggested by David Hildenbrand.
- Trim and update the commit messages, as requested by Dave Hansen.

Muchun Song (4):
  mm: fix missing page-table destructor in pagetable_free()
  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 | 32 +++++++++++++-------------------
 include/linux/mm.h   | 37 ++++++++++++++++++++-----------------
 3 files changed, 34 insertions(+), 38 deletions(-)


base-commit: 8b38ed9ab5b09c8ba168cbcc49524e9b380ee5c4
-- 
2.54.0