Re: [PATCH v3 4/4] riscv: Improve flush_tlb_kernel_range()

[Lad, Prabhakar]

Hi Alexandre,

On Tue, Aug 1, 2023 at 9:58 AM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/tlbflush.h | 11 +++++-----
>  arch/riscv/mm/tlbflush.c          | 34 +++++++++++++++++++++++--------
>  2 files changed, 31 insertions(+), 14 deletions(-)
>
After applying this patch, I am seeing module load issues on RZ/Five
(complete log [0]). I am testing defconfig + [1] (rz/five related
configs).

Any pointers on what could be an issue here?

[0] https://paste.debian.net/1291116/
[1] https://paste.debian.net/1291118/

Cheers,
Prabhakar

> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index f5c4fb0ae642..7426fdcd8ec5 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -37,6 +37,7 @@ 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,
> @@ -53,15 +54,15 @@ 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 0c955c474f3a..687808013758 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -120,18 +120,27 @@ 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);
> -       unsigned int cpuid;
> +       struct cpumask *cmask, full_cmask;
>         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;
> +       } else {
> +               cpumask_setall(&full_cmask);
> +               cmask = &full_cmask;
> +               broadcast = true;
> +       }
>
> -       cpuid = get_cpu();
> -       /* check if the tlbflush needs to be sent to other CPUs */
> -       broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
>         if (static_branch_unlikely(&use_asid_allocator)) {
> -               unsigned long asid = atomic_long_read(&mm->context.id) & asid_mask;
> +               unsigned long asid = mm ? atomic_long_read(&mm->context.id) & asid_mask : 0;
>
>                 if (broadcast) {
>                         if (riscv_use_ipi_for_rfence()) {
> @@ -165,7 +174,8 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
>                 }
>         }
>
> -       put_cpu();
> +       if (mm)
> +               put_cpu();
>  }
>
>  void flush_tlb_mm(struct mm_struct *mm)
> @@ -196,6 +206,12 @@ 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, 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
>
>