Re: [PATCH] riscv: Only flush the mm icache when setting an exec pte

[Charlie Jenkins]

On Fri, Feb 02, 2024 at 01:47:11PM +0100, Alexandre Ghiti wrote:
> We used to emit a flush_icache_all() whenever a dirty executable
> mapping is set in the page table but we can instead call
> flush_icache_mm() which will only send IPIs to cores that currently run
> this mm and add a deferred icache flush to the others.
> 
> The number of calls to sbi_remote_fence_i() (tested without IPI
> support):
> 
> With a simple buildroot rootfs:
> * Before: ~5k
> * After :  4 (!)
> 
> Tested on HW, the boot to login is ~4.5% faster.
> 
> With an ubuntu rootfs:
> * Before: ~24k
> * After : ~13k
> 
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/pgtable.h | 14 +++++++-------
>  arch/riscv/mm/cacheflush.c       |  4 ++--
>  arch/riscv/mm/pgtable.c          |  2 +-
>  3 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 0c94260b5d0c..058cfa89dd29 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -513,12 +513,12 @@ static inline void set_pte(pte_t *ptep, pte_t pteval)
>  	WRITE_ONCE(*ptep, pteval);
>  }
>  
> -void flush_icache_pte(pte_t pte);
> +void flush_icache_pte(struct mm_struct *mm, pte_t pte);
>  
> -static inline void __set_pte_at(pte_t *ptep, pte_t pteval)
> +static inline void __set_pte_at(struct mm_struct *mm, pte_t *ptep, pte_t pteval)
>  {
>  	if (pte_present(pteval) && pte_exec(pteval))
> -		flush_icache_pte(pteval);
> +		flush_icache_pte(mm, pteval);
>  
>  	set_pte(ptep, pteval);
>  }
> @@ -529,7 +529,7 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
>  	page_table_check_ptes_set(mm, ptep, pteval, nr);
>  
>  	for (;;) {
> -		__set_pte_at(ptep, pteval);
> +		__set_pte_at(mm, ptep, pteval);
>  		if (--nr == 0)
>  			break;
>  		ptep++;
> @@ -541,7 +541,7 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
>  static inline void pte_clear(struct mm_struct *mm,
>  	unsigned long addr, pte_t *ptep)
>  {
> -	__set_pte_at(ptep, __pte(0));
> +	__set_pte_at(mm, ptep, __pte(0));
>  }
>  
>  #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS	/* defined in mm/pgtable.c */
> @@ -707,14 +707,14 @@ static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
>  				pmd_t *pmdp, pmd_t pmd)
>  {
>  	page_table_check_pmd_set(mm, pmdp, pmd);
> -	return __set_pte_at((pte_t *)pmdp, pmd_pte(pmd));
> +	return __set_pte_at(mm, (pte_t *)pmdp, pmd_pte(pmd));
>  }
>  
>  static inline void set_pud_at(struct mm_struct *mm, unsigned long addr,
>  				pud_t *pudp, pud_t pud)
>  {
>  	page_table_check_pud_set(mm, pudp, pud);
> -	return __set_pte_at((pte_t *)pudp, pud_pte(pud));
> +	return __set_pte_at(mm, (pte_t *)pudp, pud_pte(pud));
>  }
>  
>  #ifdef CONFIG_PAGE_TABLE_CHECK
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index b0774993c0f3..3e234e95d952 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -85,12 +85,12 @@ void flush_icache_mm(struct mm_struct *mm, bool local)
>  #endif /* CONFIG_SMP */
>  
>  #ifdef CONFIG_MMU
> -void flush_icache_pte(pte_t pte)
> +void flush_icache_pte(struct mm_struct *mm, pte_t pte)
>  {
>  	struct folio *folio = page_folio(pte_page(pte));
>  
>  	if (!test_bit(PG_dcache_clean, &folio->flags)) {
> -		flush_icache_all();
> +		flush_icache_mm(mm, false);
>  		set_bit(PG_dcache_clean, &folio->flags);
>  	}
>  }
> diff --git a/arch/riscv/mm/pgtable.c b/arch/riscv/mm/pgtable.c
> index ef887efcb679..533ec9055fa0 100644
> --- a/arch/riscv/mm/pgtable.c
> +++ b/arch/riscv/mm/pgtable.c
> @@ -10,7 +10,7 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
>  			  pte_t entry, int dirty)
>  {
>  	if (!pte_same(ptep_get(ptep), entry))
> -		__set_pte_at(ptep, entry);
> +		__set_pte_at(vma->vm_mm, ptep, entry);
>  	/*
>  	 * update_mmu_cache will unconditionally execute, handling both
>  	 * the case that the PTE changed and the spurious fault case.
> -- 
> 2.39.2
> 
> 
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Reviewed-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>