linux-kernel - Re: [PATCH v2 3/7] mm: Add batched versions of ptep_modify_prot

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Message-ID: <93411699-2e36-4a4e-bc3a-3efeb8e2260b@arm.com>
Date: Tue, 29 Apr 2025 14:09:46 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org
Cc: ryan.roberts@....com, david@...hat.com, willy@...radead.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, catalin.marinas@....com,
 will@...nel.org, Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com,
 vbabka@...e.cz, jannh@...gle.com, peterx@...hat.com, joey.gouly@....com,
 ioworker0@...il.com, baohua@...nel.org, kevin.brodsky@....com,
 quic_zhenhuah@...cinc.com, christophe.leroy@...roup.eu,
 yangyicong@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
 namit@...are.com, hughd@...gle.com, yang@...amperecomputing.com,
 ziy@...dia.com
Subject: Re: [PATCH v2 3/7] mm: Add batched versions of
 ptep_modify_prot_start/commit



On 4/29/25 10:53, Dev Jain wrote:
> Batch ptep_modify_prot_start/commit in preparation for optimizing mprotect.
> Architecture can override these helpers.
> 
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
>  include/linux/pgtable.h | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index b50447ef1c92..ed287289335f 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -891,6 +891,44 @@ static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
>  }
>  #endif
>  
> +/* See the comment for ptep_modify_prot_start */
> +#ifndef modify_prot_start_ptes
> +static inline pte_t modify_prot_start_ptes(struct vm_area_struct *vma,
> +		unsigned long addr, pte_t *ptep, unsigned int nr)
> +{
> +	pte_t pte, tmp_pte;
> +
> +	pte = ptep_modify_prot_start(vma, addr, ptep);
> +	while (--nr) {
> +		ptep++;
> +		addr += PAGE_SIZE;
> +		tmp_pte = ptep_modify_prot_start(vma, addr, ptep);
> +		if (pte_dirty(tmp_pte))
> +			pte = pte_mkdirty(pte);
> +		if (pte_young(tmp_pte))
> +			pte = pte_mkyoung(pte);
> +	}
> +	return pte;
> +}
> +#endif
> +
> +/* See the comment for ptep_modify_prot_commit */
> +#ifndef modify_prot_commit_ptes
> +static inline void modify_prot_commit_ptes(struct vm_area_struct *vma, unsigned long addr,
> +		pte_t *ptep, pte_t old_pte, pte_t pte, unsigned int nr)
> +{
> +	for (;;) {
> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, pte);
> +		if (--nr == 0)
> +			break;
> +		ptep++;
> +		addr += PAGE_SIZE;
> +		old_pte = pte_next_pfn(old_pte);
> +		pte = pte_next_pfn(pte);
> +	}
> +}
> +#endif

Is there any particular reason why the first loop here is while { }
based where as the second one is a for { } loop ?

> +
>  /*
>   * On some architectures hardware does not set page access bit when accessing
>   * memory page, it is responsibility of software setting this bit. It brings

These helpers should be added with at least a single caller using them.