From 2a8a0f420f74425bf5f80760fd14d7a2c3abb87d Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Wed, 25 May 2022 12:23:57 +1000 Subject: powerpc/64s: POWER10 nest MMU can upgrade PTE access authority without TLB flush The nest MMU in POWER9 does not re-fetch the PTE in response to permission mismatch, contrary to the architecture[*] and unlike the core MMU. This requires a TLB flush before upgrading permissions of valid PTEs, for any address space with a coprocessor attached. Per (non-public) Nest MMU Workbook, POWER10 nest MMU conforms to the architecture in this regard, so skip the workaround. [*] See: Power ISA Version 3.1B, 6.10.1.2 Modifying a Translation Table Entry, Setting a Reference or Change Bit or Upgrading Access Authority (PTE Subject to Atomic Hardware Updates): "If the only change being made to a valid PTE that is subject to atomic hardware updates is to set the Reference or Change bit to 1 or to upgrade access authority, a simpler sequence suffices because the translation hardware will refetch the PTE if an access is attempted for which the only problems were reference and/or change bits needing to be set or insufficient access authority." Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20220525022358.780745-3-npiggin@gmail.com --- arch/powerpc/mm/book3s64/radix_pgtable.c | 35 ++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 13 deletions(-) (limited to 'arch/powerpc/mm/book3s64/radix_pgtable.c') diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c index db2f3d193448..698274109c91 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -1018,16 +1018,21 @@ void radix__ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep, unsigned long change = pte_val(entry) ^ pte_val(*ptep); /* - * To avoid NMMU hang while relaxing access, we need mark - * the pte invalid in between. + * On POWER9, the NMMU is not able to relax PTE access permissions + * for a translation with a TLB. The PTE must be invalidated, TLB + * flushed before the new PTE is installed. + * + * This only needs to be done for radix, because hash translation does + * flush when updating the linux pte (and we don't support NMMU + * accelerators on HPT on POWER9 anyway XXX: do we?). + * + * POWER10 (and P9P) NMMU does behave as per ISA. */ - if ((change & _PAGE_RW) && atomic_read(&mm->context.copros) > 0) { + if (!cpu_has_feature(CPU_FTR_ARCH_31) && (change & _PAGE_RW) && + atomic_read(&mm->context.copros) > 0) { unsigned long old_pte, new_pte; old_pte = __radix_pte_update(ptep, _PAGE_PRESENT, _PAGE_INVALID); - /* - * new value of pte - */ new_pte = old_pte | set; radix__flush_tlb_page_psize(mm, address, psize); __radix_pte_update(ptep, _PAGE_INVALID, new_pte); @@ -1035,9 +1040,12 @@ void radix__ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep, __radix_pte_update(ptep, 0, set); /* * Book3S does not require a TLB flush when relaxing access - * restrictions when the address space is not attached to a - * NMMU, because the core MMU will reload the pte after taking - * an access fault, which is defined by the architecture. + * restrictions when the address space (modulo the POWER9 nest + * MMU issue above) because the MMU will reload the PTE after + * taking an access fault, as defined by the architecture. See + * "Setting a Reference or Change Bit or Upgrading Access + * Authority (PTE Subject to Atomic Hardware Updates)" in + * Power ISA Version 3.1B. */ } /* See ptesync comment in radix__set_pte_at */ @@ -1050,11 +1058,12 @@ void radix__ptep_modify_prot_commit(struct vm_area_struct *vma, struct mm_struct *mm = vma->vm_mm; /* - * To avoid NMMU hang while relaxing access we need to flush the tlb before - * we set the new value. We need to do this only for radix, because hash - * translation does flush when updating the linux pte. + * POWER9 NMMU must flush the TLB after clearing the PTE before + * installing a PTE with more relaxed access permissions, see + * radix__ptep_set_access_flags. */ - if (is_pte_rw_upgrade(pte_val(old_pte), pte_val(pte)) && + if (!cpu_has_feature(CPU_FTR_ARCH_31) && + is_pte_rw_upgrade(pte_val(old_pte), pte_val(pte)) && (atomic_read(&mm->context.copros) > 0)) radix__flush_tlb_page(vma, addr); -- cgit v1.2.3