From 073ebebd186250038a04be9693240f90f398c4b1 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Fri, 26 Jul 2024 17:07:28 +0200 Subject: [PATCH] powerpc/8xx: document and enforce that split PT locks are not used Right now, we cannot have split PT locks because 8xx does not support SMP. But for the sake of documentation *why* 8xx is fine regarding what we documented in huge_pte_lockptr(), let's just add code to enforce it at the same time as documenting it. This should also make everybody who wants to copy from the 8xx approach of supporting such unusual ways of mapping hugetlb folios aware that it gets tricky once multiple page tables are involved. Link: https://lkml.kernel.org/r/20240726150728.3159964-4-david@redhat.com Signed-off-by: David Hildenbrand Cc: Alexander Viro Cc: Borislav Petkov Cc: Boris Ostrovsky Cc: Christian Brauner Cc: Christophe Leroy Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Juergen Gross Cc: Michael Ellerman Cc: Mike Rapoport (Microsoft) Cc: Muchun Song Cc: "Naveen N. Rao" Cc: Nicholas Piggin Cc: Oscar Salvador Cc: Peter Xu Cc: Russell King Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- arch/powerpc/mm/pgtable.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c index ab0656115424..7316396e452d 100644 --- a/arch/powerpc/mm/pgtable.c +++ b/arch/powerpc/mm/pgtable.c @@ -297,6 +297,12 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, } #if defined(CONFIG_PPC_8xx) + +#if defined(CONFIG_SPLIT_PTE_PTLOCKS) || defined(CONFIG_SPLIT_PMD_PTLOCKS) +/* We need the same lock to protect the PMD table and the two PTE tables. */ +#error "8M hugetlb folios are incompatible with split page table locks" +#endif + static void __set_huge_pte_at(pmd_t *pmd, pte_t *ptep, pte_basic_t val) { pte_basic_t *entry = (pte_basic_t *)ptep; -- 2.25.1