From e5f7cb58c2b77a0249c2028b6d1ec4d6d420816d Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Fri, 1 Jun 2018 20:01:15 +1000 Subject: [PATCH] powerpc/64s/radix: do not flush TLB when relaxing access Radix flushes the TLB when updating ptes to increase permissiveness of protection (increase access authority). Book3S does not require TLB flushing in this case, and it is not done on hash. This patch avoids the flush for radix. >From Power ISA v3.0B, p.1090: 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 add access authorities, 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. The nest MMU on POWER9 does not re-fetch the PTE after such an access attempt before faulting, so address spaces with a coprocessor attached will continue to flush in these cases. This reduces tlbies for a kernel compile workload from 1.28M to 0.95M, tlbiels from 20.17M 19.68M. fork --fork --exec benchmark improved 2.77% (12000->12300). Reviewed-by: Aneesh Kumar K.V Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman --- arch/powerpc/mm/pgtable-radix.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c index 0ddfe591cd24..d6f74cbf0fed 100644 --- a/arch/powerpc/mm/pgtable-radix.c +++ b/arch/powerpc/mm/pgtable-radix.c @@ -1108,7 +1108,12 @@ void radix__ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep, __radix_pte_update(ptep, 0, new_pte); } else { __radix_pte_update(ptep, 0, set); - radix__flush_tlb_page_psize(mm, address, psize); + /* + * 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 architectue. + */ } asm volatile("ptesync" : : : "memory"); }