Re: [PATCH v7 2/3] mm/arm64: override clear_young_dirty_ptes() batch helper

[Ryan Roberts]

On 16/04/2024 04:34, Lance Yang wrote:
> The per-pte get_and_clear/modify/set approach would result in
> unfolding/refolding for contpte mappings on arm64. So we need
> to override clear_young_dirty_ptes() for arm64 to avoid it.
> 
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Suggested-by: Barry Song <21cnbao@xxxxxxxxx>
> Suggested-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>

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

> ---
>  arch/arm64/include/asm/pgtable.h | 55 ++++++++++++++++++++++++++++++++
>  arch/arm64/mm/contpte.c          | 29 +++++++++++++++++
>  2 files changed, 84 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 9fd8613b2db2..1303d30287dc 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1223,6 +1223,46 @@ static inline void __wrprotect_ptes(struct mm_struct *mm, unsigned long address,
>  		__ptep_set_wrprotect(mm, address, ptep);
>  }
>  
> +static inline void __clear_young_dirty_pte(struct vm_area_struct *vma,
> +					   unsigned long addr, pte_t *ptep,
> +					   pte_t pte, cydp_t flags)
> +{
> +	pte_t old_pte;
> +
> +	do {
> +		old_pte = pte;
> +
> +		if (flags & CYDP_CLEAR_YOUNG)
> +			pte = pte_mkold(pte);
> +		if (flags & CYDP_CLEAR_DIRTY)
> +			pte = pte_mkclean(pte);
> +
> +		pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
> +					       pte_val(old_pte), pte_val(pte));
> +	} while (pte_val(pte) != pte_val(old_pte));
> +}
> +
> +static inline void __clear_young_dirty_ptes(struct vm_area_struct *vma,
> +					    unsigned long addr, pte_t *ptep,
> +					    unsigned int nr, cydp_t flags)
> +{
> +	pte_t pte;
> +
> +	for (;;) {
> +		pte = __ptep_get(ptep);
> +
> +		if (flags == (CYDP_CLEAR_YOUNG | CYDP_CLEAR_DIRTY))
> +			__set_pte(ptep, pte_mkclean(pte_mkold(pte)));
> +		else
> +			__clear_young_dirty_pte(vma, addr, ptep, pte, flags);
> +
> +		if (--nr == 0)
> +			break;
> +		ptep++;
> +		addr += PAGE_SIZE;
> +	}
> +}
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  #define __HAVE_ARCH_PMDP_SET_WRPROTECT
>  static inline void pmdp_set_wrprotect(struct mm_struct *mm,
> @@ -1379,6 +1419,9 @@ extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
>  extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
>  				unsigned long addr, pte_t *ptep,
>  				pte_t entry, int dirty);
> +extern void contpte_clear_young_dirty_ptes(struct vm_area_struct *vma,
> +				unsigned long addr, pte_t *ptep,
> +				unsigned int nr, cydp_t flags);
>  
>  static __always_inline void contpte_try_fold(struct mm_struct *mm,
>  				unsigned long addr, pte_t *ptep, pte_t pte)
> @@ -1603,6 +1646,17 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma,
>  	return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty);
>  }
>  
> +#define clear_young_dirty_ptes clear_young_dirty_ptes
> +static inline void clear_young_dirty_ptes(struct vm_area_struct *vma,
> +					  unsigned long addr, pte_t *ptep,
> +					  unsigned int nr, cydp_t flags)
> +{
> +	if (likely(nr == 1 && !pte_cont(__ptep_get(ptep))))
> +		__clear_young_dirty_ptes(vma, addr, ptep, nr, flags);
> +	else
> +		contpte_clear_young_dirty_ptes(vma, addr, ptep, nr, flags);
> +}
> +
>  #else /* CONFIG_ARM64_CONTPTE */
>  
>  #define ptep_get				__ptep_get
> @@ -1622,6 +1676,7 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma,
>  #define wrprotect_ptes				__wrprotect_ptes
>  #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
>  #define ptep_set_access_flags			__ptep_set_access_flags
> +#define clear_young_dirty_ptes			__clear_young_dirty_ptes
>  
>  #endif /* CONFIG_ARM64_CONTPTE */
>  
> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
> index 1b64b4c3f8bf..9f9486de0004 100644
> --- a/arch/arm64/mm/contpte.c
> +++ b/arch/arm64/mm/contpte.c
> @@ -361,6 +361,35 @@ void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
>  }
>  EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes);
>  
> +void contpte_clear_young_dirty_ptes(struct vm_area_struct *vma,
> +				    unsigned long addr, pte_t *ptep,
> +				    unsigned int nr, cydp_t flags)
> +{
> +	/*
> +	 * We can safely clear access/dirty without needing to unfold from
> +	 * the architectures perspective, even when contpte is set. If the
> +	 * range starts or ends midway through a contpte block, we can just
> +	 * expand to include the full contpte block. While this is not
> +	 * exactly what the core-mm asked for, it tracks access/dirty per
> +	 * folio, not per page. And since we only create a contpte block
> +	 * when it is covered by a single folio, we can get away with
> +	 * clearing access/dirty for the whole block.
> +	 */
> +	unsigned long start = addr;
> +	unsigned long end = start + nr;
> +
> +	if (pte_cont(__ptep_get(ptep + nr - 1)))
> +		end = ALIGN(end, CONT_PTE_SIZE);
> +
> +	if (pte_cont(__ptep_get(ptep))) {
> +		start = ALIGN_DOWN(start, CONT_PTE_SIZE);
> +		ptep = contpte_align_down(ptep);
> +	}
> +
> +	__clear_young_dirty_ptes(vma, start, ptep, end - start, flags);
> +}
> +EXPORT_SYMBOL_GPL(contpte_clear_young_dirty_ptes);
> +
>  int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
>  					unsigned long addr, pte_t *ptep,
>  					pte_t entry, int dirty)