[PATCH 1/2] powerpc/64s/radix: do not flush TLB when relaxing access

[Balbir Singh]

On Wed, May 9, 2018 at 4:51 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
> 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.
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>  arch/powerpc/mm/pgtable-book3s64.c | 1 -
>  arch/powerpc/mm/pgtable.c          | 3 ++-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
> index 518518fb7c45..6e991eaccab4 100644
> --- a/arch/powerpc/mm/pgtable-book3s64.c
> +++ b/arch/powerpc/mm/pgtable-book3s64.c
> @@ -40,7 +40,6 @@ int pmdp_set_access_flags(struct vm_area_struct *vma, unsigned long address,
>         if (changed) {
>                 __ptep_set_access_flags(vma->vm_mm, pmdp_ptep(pmdp),
>                                         pmd_pte(entry), address);
> -               flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);

The comment states that this can be used for missing execution
permissions as well. I am not convinced we can skip a flush in those
cases

>         }
>         return changed;
>  }
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index 9f361ae571e9..5b07a626df5b 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -224,7 +224,8 @@ int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
>                 if (!is_vm_hugetlb_page(vma))
>                         assert_pte_locked(vma->vm_mm, address);
>                 __ptep_set_access_flags(vma->vm_mm, ptep, entry, address);
> -               flush_tlb_page(vma, address);
> +               if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64))
> +                       flush_tlb_page(vma, address);

Same as above

Balbir Singh.