Re: [PATCH v7 13/20] mm/memory: Add vmf_insert_page_mkwrite()

[David Hildenbrand <david@redhat.com>]

On 04.02.25 23:48, Alistair Popple wrote:
> Currently to map a DAX page the DAX driver calls vmf_insert_pfn. This
> creates a special devmap PTE entry for the pfn but does not take a
> reference on the underlying struct page for the mapping. This is
> because DAX page refcounts are treated specially, as indicated by the
> presence of a devmap entry.
> 
> To allow DAX page refcounts to be managed the same as normal page
> refcounts introduce vmf_insert_page_mkwrite(). This will take a
> reference on the underlying page much the same as vmf_insert_page,
> except it also permits upgrading an existing mapping to be writable if
> requested/possible.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> 
> ---
> 
> Changes for v7:
>   - Fix vmf_insert_page_mkwrite by removing pfn gunk as suggested by
>     David.
> 
> Updates from v2:
> 
>   - Rename function to make not DAX specific
> 
>   - Split the insert_page_into_pte_locked() change into a separate
>     patch.
> 
> Updates from v1:
> 
>   - Re-arrange code in insert_page_into_pte_locked() based on comments
>     from Jan Kara.
> 
>   - Call mkdrity/mkyoung for the mkwrite case, also suggested by Jan.
> ---
>   include/linux/mm.h |  2 ++
>   mm/memory.c        | 21 +++++++++++++++++++++
>   2 files changed, 23 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7b1068d..6567ece 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3544,6 +3544,8 @@ int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
>   				unsigned long num);
>   int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
>   				unsigned long num);
> +vm_fault_t vmf_insert_page_mkwrite(struct vm_fault *vmf, struct page *page,
> +			bool write);
>   vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>   			unsigned long pfn);
>   vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
> diff --git a/mm/memory.c b/mm/memory.c
> index 41befd9..b88b488 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2622,6 +2622,27 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
>   	return VM_FAULT_NOPAGE;
>   }
>   
> +vm_fault_t vmf_insert_page_mkwrite(struct vm_fault *vmf, struct page *page,
> +			bool write)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	pgprot_t pgprot = vma->vm_page_prot;

Probably could have avoided that temp without harming readability

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb