Re: [PATCH v1] mm: Remove arch_flush_tlb_batched_pending() arch helper

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 09/06/25 4:01 PM, Ryan Roberts wrote:
> Since commit 4b634918384c ("arm64/mm: Close theoretical race where stale
> TLB entry remains valid"), all arches that use tlbbatch for reclaim
> (arm64, riscv, x86) implement arch_flush_tlb_batched_pending() with a
> flush_tlb_mm().
> 
> So let's simplify by removing the unnecessary abstraction and doing the
> flush_tlb_mm() directly in flush_tlb_batched_pending(). This effectively
> reverts commit db6c1f6f236d ("mm/tlbbatch: introduce
> arch_flush_tlb_batched_pending()").
> 
> Suggested-by: Will Deacon <will@kernel.org>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Makes sense to replace arch callbacks with common generic functions
applicable for all platforms.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>


> ---
>  arch/arm64/include/asm/tlbflush.h | 11 -----------
>  arch/riscv/include/asm/tlbflush.h |  1 -
>  arch/riscv/mm/tlbflush.c          |  5 -----
>  arch/x86/include/asm/tlbflush.h   |  5 -----
>  mm/rmap.c                         |  2 +-
>  5 files changed, 1 insertion(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index aa9efee17277..18a5dc0c9a54 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -322,17 +322,6 @@ static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
>  	return true;
>  }
> 
> -/*
> - * If mprotect/munmap/etc occurs during TLB batched flushing, we need to ensure
> - * all the previously issued TLBIs targeting mm have completed. But since we
> - * can be executing on a remote CPU, a DSB cannot guarantee this like it can
> - * for arch_tlbbatch_flush(). Our only option is to flush the entire mm.
> - */
> -static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm)
> -{
> -	flush_tlb_mm(mm);
> -}
> -
>  /*
>   * To support TLB batched flush for multiple pages unmapping, we only send
>   * the TLBI for each page in arch_tlbbatch_add_pending() and wait for the
> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index 1a20dd746a49..eed0abc40514 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -63,7 +63,6 @@ void flush_pud_tlb_range(struct vm_area_struct *vma, unsigned long start,
>  bool arch_tlbbatch_should_defer(struct mm_struct *mm);
>  void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch,
>  		struct mm_struct *mm, unsigned long start, unsigned long end);
> -void arch_flush_tlb_batched_pending(struct mm_struct *mm);
>  void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch);
> 
>  extern unsigned long tlb_flush_all_threshold;
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index e737ba7949b1..8404530ec00f 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -234,11 +234,6 @@ void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch,
>  	mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end);
>  }
> 
> -void arch_flush_tlb_batched_pending(struct mm_struct *mm)
> -{
> -	flush_tlb_mm(mm);
> -}
> -
>  void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
>  {
>  	__flush_tlb_range(NULL, &batch->cpumask,
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index e9b81876ebe4..00daedfefc1b 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -356,11 +356,6 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b
>  	mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL);
>  }
> 
> -static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm)
> -{
> -	flush_tlb_mm(mm);
> -}
> -
>  extern void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch);
> 
>  static inline bool pte_flags_need_flush(unsigned long oldflags,
> diff --git a/mm/rmap.c b/mm/rmap.c
> index fb63d9256f09..fd160ddaa980 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -746,7 +746,7 @@ void flush_tlb_batched_pending(struct mm_struct *mm)
>  	int flushed = batch >> TLB_FLUSH_BATCH_FLUSHED_SHIFT;
> 
>  	if (pending != flushed) {
> -		arch_flush_tlb_batched_pending(mm);
> +		flush_tlb_mm(mm);
>  		/*
>  		 * If the new TLB flushing is pending during flushing, leave
>  		 * mm->tlb_flush_batched as is, to avoid losing flushing.
> --
> 2.43.0
> 
>