Re: [PATCH v4 4/4] riscv: Improve flush_tlb_kernel_range()

[Alexandre Ghiti <alexghiti@rivosinc.com>]

@Lad, Prabhakar Any chance you give a try to this new patchset? So
that we make sure Samuel found your issue :)

On Mon, Sep 11, 2023 at 3:16 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> This function used to simply flush the whole tlb of all harts, be more
> subtile and try to only flush the range.
>
> The problem is that we can only use PAGE_SIZE as stride since we don't know
> the size of the underlying mapping and then this function will be improved
> only if the size of the region to flush is < threshold * PAGE_SIZE.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>  arch/riscv/include/asm/tlbflush.h | 11 ++++++-----
>  arch/riscv/mm/tlbflush.c          | 33 ++++++++++++++++++++++---------
>  2 files changed, 30 insertions(+), 14 deletions(-)
>
> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index 170a49c531c6..8f3418c5f172 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -40,6 +40,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
>  void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
>                      unsigned long end);
> +void flush_tlb_kernel_range(unsigned long start, unsigned long end);
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
>  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
> @@ -56,15 +57,15 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
>         local_flush_tlb_all();
>  }
>
> -#define flush_tlb_mm(mm) flush_tlb_all()
> -#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
> -#endif /* !CONFIG_SMP || !CONFIG_MMU */
> -
>  /* Flush a range of kernel pages */
>  static inline void flush_tlb_kernel_range(unsigned long start,
>         unsigned long end)
>  {
> -       flush_tlb_all();
> +       local_flush_tlb_all();
>  }
>
> +#define flush_tlb_mm(mm) flush_tlb_all()
> +#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
> +#endif /* !CONFIG_SMP || !CONFIG_MMU */
> +
>  #endif /* _ASM_RISCV_TLBFLUSH_H */
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 2c1136d73411..28cd8539b575 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -97,19 +97,27 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
>                               unsigned long size, unsigned long stride)
>  {
>         struct flush_tlb_range_data ftd;
> -       struct cpumask *cmask = mm_cpumask(mm);
> +       struct cpumask *cmask, full_cmask;
>         unsigned long asid = FLUSH_TLB_NO_ASID;
> -       unsigned int cpuid;
>         bool broadcast;
>
> -       if (cpumask_empty(cmask))
> -               return;
> +       if (mm) {
> +               unsigned int cpuid;
> +
> +               cmask = mm_cpumask(mm);
> +               if (cpumask_empty(cmask))
> +                       return;
>
> -       cpuid = get_cpu();
> -       /* check if the tlbflush needs to be sent to other CPUs */
> -       broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
> +               cpuid = get_cpu();
> +               /* check if the tlbflush needs to be sent to other CPUs */
> +               broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
> +       } else {
> +               cpumask_setall(&full_cmask);
> +               cmask = &full_cmask;
> +               broadcast = true;
> +       }
>
> -       if (static_branch_unlikely(&use_asid_allocator))
> +       if (static_branch_unlikely(&use_asid_allocator) && mm)
>                 asid = atomic_long_read(&mm->context.id) & asid_mask;
>
>         if (broadcast) {
> @@ -128,7 +136,8 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
>                 local_flush_tlb_range_asid(start, size, stride, asid);
>         }
>
> -       put_cpu();
> +       if (mm)
> +               put_cpu();
>  }
>
>  void flush_tlb_mm(struct mm_struct *mm)
> @@ -189,6 +198,12 @@ void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
>
>         __flush_tlb_range(vma->vm_mm, start, end - start, stride_size);
>  }
> +
> +void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> +{
> +       __flush_tlb_range(NULL, start, end - start, PAGE_SIZE);
> +}
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
>                         unsigned long end)
> --
> 2.39.2
>