Re: [PATCH v1 05/16] mm/page_table_check: Batch-check pmds/puds just like ptes

[Anshuman Khandual]

On 2/5/25 20:39, Ryan Roberts wrote:
> Convert page_table_check_p[mu]d_set(...) to
> page_table_check_p[mu]ds_set(..., nr) to allow checking a contiguous set
> of pmds/puds in single batch. We retain page_table_check_p[mu]d_set(...)
> as macros that call new batch functions with nr=1 for compatibility.
> 
> arm64 is about to reorganise its pte/pmd/pud helpers to reuse more code
> and to allow the implementation for huge_pte to more efficiently set
> ptes/pmds/puds in batches. We need these batch-helpers to make the
> refactoring possible.

A very small nit.

Although this justification here is reasonable enough but not sure if
platform specific requirements, need to be spelled out in such detail
for a generic MM change.

> 
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---

Regardless, LGTM.

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

>  include/linux/page_table_check.h | 30 +++++++++++++++++-----------
>  mm/page_table_check.c            | 34 +++++++++++++++++++-------------
>  2 files changed, 38 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/page_table_check.h b/include/linux/page_table_check.h
> index 6722941c7cb8..289620d4aad3 100644
> --- a/include/linux/page_table_check.h
> +++ b/include/linux/page_table_check.h
> @@ -19,8 +19,10 @@ void __page_table_check_pmd_clear(struct mm_struct *mm, pmd_t pmd);
>  void __page_table_check_pud_clear(struct mm_struct *mm, pud_t pud);
>  void __page_table_check_ptes_set(struct mm_struct *mm, pte_t *ptep, pte_t pte,
>  		unsigned int nr);
> -void __page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd);
> -void __page_table_check_pud_set(struct mm_struct *mm, pud_t *pudp, pud_t pud);
> +void __page_table_check_pmds_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd,
> +		unsigned int nr);
> +void __page_table_check_puds_set(struct mm_struct *mm, pud_t *pudp, pud_t pud,
> +		unsigned int nr);
>  void __page_table_check_pte_clear_range(struct mm_struct *mm,
>  					unsigned long addr,
>  					pmd_t pmd);
> @@ -74,22 +76,22 @@ static inline void page_table_check_ptes_set(struct mm_struct *mm,
>  	__page_table_check_ptes_set(mm, ptep, pte, nr);
>  }
>  
> -static inline void page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp,
> -					    pmd_t pmd)
> +static inline void page_table_check_pmds_set(struct mm_struct *mm,
> +		pmd_t *pmdp, pmd_t pmd, unsigned int nr)
>  {
>  	if (static_branch_likely(&page_table_check_disabled))
>  		return;
>  
> -	__page_table_check_pmd_set(mm, pmdp, pmd);
> +	__page_table_check_pmds_set(mm, pmdp, pmd, nr);
>  }
>  
> -static inline void page_table_check_pud_set(struct mm_struct *mm, pud_t *pudp,
> -					    pud_t pud)
> +static inline void page_table_check_puds_set(struct mm_struct *mm,
> +		pud_t *pudp, pud_t pud, unsigned int nr)
>  {
>  	if (static_branch_likely(&page_table_check_disabled))
>  		return;
>  
> -	__page_table_check_pud_set(mm, pudp, pud);
> +	__page_table_check_puds_set(mm, pudp, pud, nr);
>  }
>  
>  static inline void page_table_check_pte_clear_range(struct mm_struct *mm,
> @@ -129,13 +131,13 @@ static inline void page_table_check_ptes_set(struct mm_struct *mm,
>  {
>  }
>  
> -static inline void page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp,
> -					    pmd_t pmd)
> +static inline void page_table_check_pmds_set(struct mm_struct *mm,
> +		pmd_t *pmdp, pmd_t pmd, unsigned int nr)
>  {
>  }
>  
> -static inline void page_table_check_pud_set(struct mm_struct *mm, pud_t *pudp,
> -					    pud_t pud)
> +static inline void page_table_check_puds_set(struct mm_struct *mm,
> +		pud_t *pudp, pud_t pud, unsigned int nr)
>  {
>  }
>  
> @@ -146,4 +148,8 @@ static inline void page_table_check_pte_clear_range(struct mm_struct *mm,
>  }
>  
>  #endif /* CONFIG_PAGE_TABLE_CHECK */
> +
> +#define page_table_check_pmd_set(mm, pmdp, pmd)	page_table_check_pmds_set(mm, pmdp, pmd, 1)
> +#define page_table_check_pud_set(mm, pudp, pud)	page_table_check_puds_set(mm, pudp, pud, 1)
> +
>  #endif /* __LINUX_PAGE_TABLE_CHECK_H */
> diff --git a/mm/page_table_check.c b/mm/page_table_check.c
> index 509c6ef8de40..dae4a7d776b3 100644
> --- a/mm/page_table_check.c
> +++ b/mm/page_table_check.c
> @@ -234,33 +234,39 @@ static inline void page_table_check_pmd_flags(pmd_t pmd)
>  		WARN_ON_ONCE(swap_cached_writable(pmd_to_swp_entry(pmd)));
>  }
>  
> -void __page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd)
> +void __page_table_check_pmds_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd,
> +		unsigned int nr)
>  {
> +	unsigned int i;
> +	unsigned long stride = PMD_SIZE >> PAGE_SHIFT;
> +
>  	if (&init_mm == mm)
>  		return;
>  
>  	page_table_check_pmd_flags(pmd);
>  
> -	__page_table_check_pmd_clear(mm, *pmdp);
> -	if (pmd_user_accessible_page(pmd)) {
> -		page_table_check_set(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT,
> -				     pmd_write(pmd));
> -	}
> +	for (i = 0; i < nr; i++)
> +		__page_table_check_pmd_clear(mm, *(pmdp + i));
> +	if (pmd_user_accessible_page(pmd))
> +		page_table_check_set(pmd_pfn(pmd), stride * nr, pmd_write(pmd));
>  }
> -EXPORT_SYMBOL(__page_table_check_pmd_set);
> +EXPORT_SYMBOL(__page_table_check_pmds_set);
>  
> -void __page_table_check_pud_set(struct mm_struct *mm, pud_t *pudp, pud_t pud)
> +void __page_table_check_puds_set(struct mm_struct *mm, pud_t *pudp, pud_t pud,
> +		unsigned int nr)
>  {
> +	unsigned int i;
> +	unsigned long stride = PUD_SIZE >> PAGE_SHIFT;
> +
>  	if (&init_mm == mm)
>  		return;
>  
> -	__page_table_check_pud_clear(mm, *pudp);
> -	if (pud_user_accessible_page(pud)) {
> -		page_table_check_set(pud_pfn(pud), PUD_SIZE >> PAGE_SHIFT,
> -				     pud_write(pud));
> -	}
> +	for (i = 0; i < nr; i++)
> +		__page_table_check_pud_clear(mm, *(pudp + i));
> +	if (pud_user_accessible_page(pud))
> +		page_table_check_set(pud_pfn(pud), stride * nr, pud_write(pud));
>  }
> -EXPORT_SYMBOL(__page_table_check_pud_set);
> +EXPORT_SYMBOL(__page_table_check_puds_set);
>  
>  void __page_table_check_pte_clear_range(struct mm_struct *mm,
>  					unsigned long addr,