Re: [PATCH 10/7] riscv: Implement the new page table range API

Yin, Fengwei
2023-02-15T08:38:41Z

On Wed, 2023-02-15 at 00:04 +0000, Matthew Wilcox (Oracle) wrote:
> Add set_ptes(), update_mmu_cache_range() and flush_dcache_folio().
>
> The PG_dcache_clear flag changes from being a per-page bit to being a
> per-folio bit.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  arch/riscv/include/asm/cacheflush.h | 19 +++++++++----------
>  arch/riscv/include/asm/pgtable.h    | 25 ++++++++++++++++++-------
>  arch/riscv/mm/cacheflush.c          | 11 ++---------
>  3 files changed, 29 insertions(+), 26 deletions(-)
>
> diff --git a/arch/riscv/include/asm/cacheflush.h
> b/arch/riscv/include/asm/cacheflush.h
> index 03e3b95ae6da..10e5e96f09b5 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -15,20 +15,19 @@ static inline void local_flush_icache_all(void)
>
>  #define PG_dcache_clean PG_arch_1
>
> -static inline void flush_dcache_page(struct page *page)
> +static inline void flush_dcache_folio(struct folio *folio)
>  {
> -       /*
> -        * HugeTLB pages are always fully mapped and only head page
> will be
> -        * set PG_dcache_clean (see comments in flush_icache_pte()).
> -        */
> -       if (PageHuge(page))
> -               page = compound_head(page);
> -
> -       if (test_bit(PG_dcache_clean, &page->flags))
> -               clear_bit(PG_dcache_clean, &page->flags);
> +       if (test_bit(PG_dcache_clean, &folio->flags))
> +               clear_bit(PG_dcache_clean, &folio->flags);
>  }
> +#define flush_dcache_folio flush_dcache_folio
>  #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
>
> +static inline void flush_dcache_page(struct page *page)
> +{
> +       flush_dcache_folio(page_folio(page));
> +}
> +
>  /*
>   * RISC-V doesn't have an instruction to flush parts of the
> instruction cache,
>   * so instead we just flush the whole thing.
> diff --git a/arch/riscv/include/asm/pgtable.h
> b/arch/riscv/include/asm/pgtable.h
> index 13222fd5c4b4..03706c833e70 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -405,8 +405,8 @@ static inline pte_t pte_modify(pte_t pte,
> pgprot_t newprot)
>
>
>  /* Commit new configuration to MMU hardware */
> -static inline void update_mmu_cache(struct vm_area_struct *vma,
> -       unsigned long address, pte_t *ptep)
> +static inline void update_mmu_cache_range(struct vm_area_struct
> *vma,
> +               unsigned long address, pte_t *ptep, unsigned int nr)
>  {
>         /*
>          * The kernel assumes that TLBs don't cache invalid entries,
> but
> @@ -415,8 +415,10 @@ static inline void update_mmu_cache(struct
> vm_area_struct *vma,
>          * Relying on flush_tlb_fix_spurious_fault would suffice, but
>          * the extra traps reduce performance.  So, eagerly
> SFENCE.VMA.
>          */
> -       flush_tlb_page(vma, address);
> +       flush_tlb_range(vma, address, address + nr * PAGE_SIZE);

The flush_tlb_range() of riscv is a little bit strange to me. It gives
__sbi_tlb_flush_range() stride PAGE_SIZE. That means if (end - start)
is larger than stride, it will trigger flush_tlb_all().

So this change could trigger flush_tlb_all() while original
flush_tlb_page() just trigger flush_tlb_page().

My understanding is flush_tlb_page() should be better because
flush_pmd_tlb_range() has PMD_SIZE as stride to avoid flush_tlb_all().
I must miss something here.

Regards
Yin, Fengwei

>  }
> +#define update_mmu_cache(vma, addr, ptep) \
> +       update_mmu_cache_range(vma, addr, ptep, 1)
>
>  #define __HAVE_ARCH_UPDATE_MMU_TLB
>  #define update_mmu_tlb update_mmu_cache
> @@ -456,12 +458,21 @@ static inline void __set_pte_at(struct
> mm_struct *mm,
>         set_pte(ptep, pteval);
>  }
>
> -static inline void set_pte_at(struct mm_struct *mm,
> -       unsigned long addr, pte_t *ptep, pte_t pteval)
> +static inline void set_ptes(struct mm_struct *mm, unsigned long
> addr,
> +               pte_t *ptep, pte_t pteval, unsigned int nr)
>  {
> -       page_table_check_ptes_set(mm, addr, ptep, pteval, 1);
> -       __set_pte_at(mm, addr, ptep, pteval);
> +       page_table_check_ptes_set(mm, addr, ptep, pteval, nr);
> +
> +       for (;;) {
> +               __set_pte_at(mm, addr, ptep, pteval);
> +               if (--nr == 0)
> +                       break;
> +               ptep++;
> +               addr += PAGE_SIZE;
> +               pte_val(pteval) += 1 << _PAGE_PFN_SHIFT;
> +       }
>  }
> +#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep,
> pte, 1)
>
>  static inline void pte_clear(struct mm_struct *mm,
>         unsigned long addr, pte_t *ptep)
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 3cc07ed45aeb..b725c3f6f57f 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -81,16 +81,9 @@ void flush_icache_mm(struct mm_struct *mm, bool
> local)
>  #ifdef CONFIG_MMU
>  void flush_icache_pte(pte_t pte)
>  {
> -       struct page *page = pte_page(pte);
> +       struct folio *folio = page_folio(pte_page(pte));
>
> -       /*
> -        * HugeTLB pages are always fully mapped, so only setting
> head page's
> -        * PG_dcache_clean flag is enough.
> -        */
> -       if (PageHuge(page))
> -               page = compound_head(page);
> -
> -       if (!test_and_set_bit(PG_dcache_clean, &page->flags))
> +       if (!test_and_set_bit(PG_dcache_clean, &folio->flags))
>                 flush_icache_all();
>  }
>  #endif /* CONFIG_MMU */