Re: [PATCH v2 2/3] mm/memory: remove the mkwrite argument from __vm_insert_mixed()

[Anshuman Khandual]

On Sat, Oct 03, 2026 at 01:05:33AM +0900, Sang-Heon Jeon wrote:
> __vm_insert_mixed() is only called from vmf_insert_mixed() with
> mkwrite == false, so mkwrite is also always false in vm_mixed_ok()
> and insert_pfn().
> 
> So remove the argument and the unreachable code in insert_pfn().
> 
> No functional change.
> 
> Signed-off-by: Sang-Heon Jeon <ekffu200098@xxxxxxxxx>

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

> ---
>  mm/memory.c | 57 +++++++++++++++++------------------------------------
>  1 file changed, 18 insertions(+), 39 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 4b2e4be28031..6c1d38eba7b2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2453,7 +2453,14 @@ static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte,
>  		if (!mkwrite)
>  			return -EBUSY;
>  
> -		/* see insert_pfn(). */
> +		/*
> +		 * For read faults on private mappings the PFN passed in may
> +		 * not match the PFN we have mapped if the mapped PFN is a
> +		 * writeable COW page.  In the mkwrite case we are creating a
> +		 * writable PTE for a shared mapping and we expect the PFNs to
> +		 * match. If they don't match, we are likely racing with block
> +		 * allocation and mapping invalidation.
> +		 */
>  		if (pte_pfn(pteval) != page_to_pfn(page)) {
>  			WARN_ON_ONCE(!is_zero_pfn(pte_pfn(pteval)));
>  			return -EFAULT;
> @@ -2858,7 +2865,7 @@ int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
>  EXPORT_SYMBOL(vm_map_pages_zero);
>  
>  static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> -			unsigned long pfn, pgprot_t prot, bool mkwrite)
> +			unsigned long pfn, pgprot_t prot)
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	pte_t *pte, entry;
> @@ -2868,38 +2875,12 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  	if (!pte)
>  		return VM_FAULT_OOM;
>  	entry = ptep_get(pte);
> -	if (!pte_none(entry)) {
> -		if (mkwrite) {
> -			/*
> -			 * For read faults on private mappings the PFN passed
> -			 * in may not match the PFN we have mapped if the
> -			 * mapped PFN is a writeable COW page.  In the mkwrite
> -			 * case we are creating a writable PTE for a shared
> -			 * mapping and we expect the PFNs to match. If they
> -			 * don't match, we are likely racing with block
> -			 * allocation and mapping invalidation so just skip the
> -			 * update.
> -			 */
> -			if (pte_pfn(entry) != pfn) {
> -				WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry)));
> -				goto out_unlock;
> -			}
> -			entry = pte_mkyoung(entry);
> -			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> -			if (ptep_set_access_flags(vma, addr, pte, entry, 1))
> -				update_mmu_cache(vma, addr, pte);
> -		}
> +	if (!pte_none(entry))
>  		goto out_unlock;
> -	}
>  
>  	/* Ok, finally just insert the thing.. */
>  	entry = pte_mkspecial(pfn_pte(pfn, prot));
>  
> -	if (mkwrite) {
> -		entry = pte_mkyoung(entry);
> -		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> -	}
> -
>  	set_pte_at(mm, addr, pte, entry);
>  	update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
>  
> @@ -2967,7 +2948,7 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
>  
>  	pfnmap_setup_cachemode_pfn(pfn, &pgprot);
>  
> -	return insert_pfn(vma, addr, pfn, pgprot, false);
> +	return insert_pfn(vma, addr, pfn, pgprot);
>  }
>  EXPORT_SYMBOL(vmf_insert_pfn_prot);
>  
> @@ -2998,11 +2979,9 @@ vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  }
>  EXPORT_SYMBOL(vmf_insert_pfn);
>  
> -static bool vm_mixed_ok(struct vm_area_struct *vma, unsigned long pfn,
> -			bool mkwrite)
> +static bool vm_mixed_ok(struct vm_area_struct *vma, unsigned long pfn)
>  {
> -	if (unlikely(is_zero_pfn(pfn)) &&
> -	    (mkwrite || !vm_mixed_zeropage_allowed(vma)))
> +	if (unlikely(is_zero_pfn(pfn)) && !vm_mixed_zeropage_allowed(vma))
>  		return false;
>  	/* these checks mirror the abort conditions in vm_normal_page */
>  	if (vma->vm_flags & VM_MIXEDMAP)
> @@ -3013,12 +2992,12 @@ static bool vm_mixed_ok(struct vm_area_struct *vma, unsigned long pfn,
>  }
>  
>  static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
> -		unsigned long addr, unsigned long pfn, bool mkwrite)
> +		unsigned long addr, unsigned long pfn)
>  {
>  	pgprot_t pgprot = vma->vm_page_prot;
>  	int err;
>  
> -	if (!vm_mixed_ok(vma, pfn, mkwrite))
> +	if (!vm_mixed_ok(vma, pfn))
>  		return VM_FAULT_SIGBUS;
>  
>  	if (addr < vma->vm_start || addr >= vma->vm_end)
> @@ -3045,9 +3024,9 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
>  		 * result in pfn_t_has_page() == false.
>  		 */
>  		page = pfn_to_page(pfn);
> -		err = insert_page(vma, addr, page, pgprot, mkwrite);
> +		err = insert_page(vma, addr, page, pgprot, false);
>  	} else {
> -		return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
> +		return insert_pfn(vma, addr, pfn, pgprot);
>  	}
>  
>  	if (err == -ENOMEM)
> @@ -3086,7 +3065,7 @@ EXPORT_SYMBOL_GPL(vmf_insert_page_mkwrite);
>  vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
>  		unsigned long pfn)
>  {
> -	return __vm_insert_mixed(vma, addr, pfn, false);
> +	return __vm_insert_mixed(vma, addr, pfn);
>  }
>  EXPORT_SYMBOL(vmf_insert_mixed);
>  
> -- 
> 2.43.0
>