Re: [RFC PATCH 8/8] powerpc/64s/radix: Only flush local TLB for spurious fault flushes

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2017-09-08 at 00:51 +1000, Nicholas Piggin wrote:
> When permissiveness is relaxed, or found to have been relaxed by
> another thread, we flush that address out of the TLB to avoid a
> future fault or micro-fault due to a stale TLB entry.
> 
> Currently for processes with TLBs on other CPUs, this flush is always
> done with a global tlbie. Although that could reduce faults on remote
> CPUs, a broadcast operation seems to be wasteful for something that
> can be handled in-core by the remote CPU if it comes to it.
> 
> This is not benchmarked yet. It does seem cut some tlbie operations
> from the bus.

What happens with the nest MMU here ?

> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  .../powerpc/include/asm/book3s/64/tlbflush-radix.h |  5 ++++
>  arch/powerpc/include/asm/book3s/64/tlbflush.h      | 11 +++++++++
>  arch/powerpc/mm/pgtable-book3s64.c                 |  5 +++-
>  arch/powerpc/mm/pgtable.c                          |  2 +-
>  arch/powerpc/mm/tlb-radix.c                        | 27 ++++++++++++++++++++++
>  5 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h b/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> index b12460b306a7..34cd864b8fc1 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> @@ -16,6 +16,8 @@ extern bool radix__flush_tlb_range_psize(struct mm_struct *mm, unsigned long sta
>  					 unsigned long end, int psize);
>  extern void radix__flush_pmd_tlb_range(struct vm_area_struct *vma,
>  				       unsigned long start, unsigned long end);
> +extern void radix__local_flush_pmd_tlb_range(struct vm_area_struct *vma,
> +				unsigned long start, unsigned long end);
>  extern void radix__flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
>  			    unsigned long end);
>  extern void radix__flush_tlb_kernel_range(unsigned long start, unsigned long end);
> @@ -24,6 +26,9 @@ extern void radix__local_flush_tlb_mm(struct mm_struct *mm);
>  extern void radix__local_flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
>  extern void radix__local_flush_tlb_page_psize(struct mm_struct *mm, unsigned long vmaddr,
>  					      int psize);
> +extern void radix__local_flush_tlb_range_psize(struct mm_struct *mm,
> +				unsigned long start, unsigned long end,
> +				int psize);
>  extern void radix__tlb_flush(struct mmu_gather *tlb);
>  #ifdef CONFIG_SMP
>  extern void radix__flush_tlb_mm(struct mm_struct *mm);
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> index 72b925f97bab..8a8b3e11a28e 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> @@ -83,6 +83,17 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
>  #define flush_tlb_mm(mm)		local_flush_tlb_mm(mm)
>  #define flush_tlb_page(vma, addr)	local_flush_tlb_page(vma, addr)
>  #endif /* CONFIG_SMP */
> +
> +#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault
> +static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma,
> +						unsigned long address)
> +{
> +	if (radix_enabled())
> +		radix__local_flush_tlb_page(vma, address);
> +	else
> +		flush_tlb_page(vma, address);
> +}
> +
>  /*
>   * flush the page walk cache for the address
>   */
> diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
> index 3b65917785a5..e46f346388d6 100644
> --- a/arch/powerpc/mm/pgtable-book3s64.c
> +++ b/arch/powerpc/mm/pgtable-book3s64.c
> @@ -40,7 +40,10 @@ 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);
> +		if (radix_enabled())
> +			radix__local_flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
> +		else
> +			flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
>  	}
>  	return changed;
>  }
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index a03ff3d99e0c..acd6ae8062ce 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -223,7 +223,7 @@ 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);
> +		flush_tlb_fix_spurious_fault(vma, address);
>  	}
>  	return changed;
>  }
> diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c
> index 7452e1f4aa3c..bcb41d037593 100644
> --- a/arch/powerpc/mm/tlb-radix.c
> +++ b/arch/powerpc/mm/tlb-radix.c
> @@ -396,6 +396,27 @@ void radix__tlb_flush(struct mmu_gather *tlb)
>  static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;
>  static unsigned long tlb_local_single_page_flush_ceiling __read_mostly = POWER9_TLB_SETS_RADIX * 2;
>  
> +void radix__local_flush_tlb_range_psize(struct mm_struct *mm,
> +				unsigned long start, unsigned long end,
> +				int psize)
> +{
> +	unsigned long pid;
> +	unsigned int page_shift = mmu_psize_defs[psize].shift;
> +	unsigned long page_size = 1UL << page_shift;
> +
> +	pid = mm ? mm->context.id : 0;
> +	if (unlikely(pid == MMU_NO_CONTEXT))
> +		return;
> +
> +	preempt_disable();
> +	if (end == TLB_FLUSH_ALL || ((end - start) >> page_shift) >
> +				tlb_local_single_page_flush_ceiling)
> +		_tlbiel_pid(pid, RIC_FLUSH_TLB);
> +	else
> +		_tlbiel_va_range(start, end, pid, page_size, psize);
> +	preempt_enable();
> +}
> +
>  static bool __radix__flush_tlb_range_psize(struct mm_struct *mm,
>  				unsigned long start, unsigned long end,
>  				int psize, bool also_pwc)
> @@ -518,6 +539,12 @@ void radix__flush_tlb_lpid(unsigned long lpid)
>  }
>  EXPORT_SYMBOL(radix__flush_tlb_lpid);
>  
> +void radix__local_flush_pmd_tlb_range(struct vm_area_struct *vma,
> +				unsigned long start, unsigned long end)
> +{
> +	radix__local_flush_tlb_range_psize(vma->vm_mm, start, end, MMU_PAGE_2M);
> +}
> +
>  void radix__flush_pmd_tlb_range(struct vm_area_struct *vma,
>  				unsigned long start, unsigned long end)
>  {