[PATCH v1 0/3] mm: split PTE/PMD PT table Kconfig cleanups+clarifications

[David Hildenbrand <david@xxxxxxxxxx>]

This series is a follow up to the fixes:
        "[PATCH v1 0/2] mm/hugetlb: fix hugetlb vs. core-mm PT locking"

When working on the fixes, I wondered why 8xx is fine (-> never uses split
PT locks) and how PT locking even works properly with PMD page table
sharing (-> always requires split PMD PT locks).

Let's improve the split PT lock detection, make hugetlb properly depend
on it and make 8xx bail out if it would ever get enabled by accident.

As an alternative to patch #3 we could extend the Kconfig SPLIT_PTE_PTLOCKS
option from patch #2 -- but enforcing it closer to the code that actually
implements it feels a bit nicer for documentation purposes, and there
is no need to actually disable it because it should always be disabled
(!SMP).

Did a bunch of cross-compilations to make sure that split PTE/PMD
PT locks are still getting used where we would expect them.

[1] https://lkml.kernel.org/r/20240725183955.2268884-1-david@xxxxxxxxxx

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>

David Hildenbrand (3):
  mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig
    options
  mm/hugetlb: enforce that PMD PT sharing has split PMD PT locks
  powerpc/8xx: document and enforce that split PT locks are not used

 arch/arm/mm/fault-armv.c      |  6 +++---
 arch/powerpc/mm/pgtable.c     |  6 ++++++
 arch/x86/xen/mmu_pv.c         |  7 ++++---
 fs/Kconfig                    |  4 ++++
 include/linux/hugetlb.h       |  5 ++---
 include/linux/mm.h            |  8 ++++----
 include/linux/mm_types.h      |  2 +-
 include/linux/mm_types_task.h |  3 ---
 kernel/fork.c                 |  4 ++--
 mm/Kconfig                    | 18 +++++++++++-------
 mm/hugetlb.c                  |  8 ++++----
 mm/memory.c                   |  2 +-
 12 files changed, 42 insertions(+), 31 deletions(-)

-- 
2.45.2