linux-kernel - Re: [PATCH v7 13/20] mm/memory: Add vmf_insert_page

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Message-ID: <0c8640f5-2a80-45ff-a922-476a5fd5f82d@redhat.com>
Date: Mon, 10 Feb 2025 19:40:56 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org,
 dan.j.williams@...el.com, linux-mm@...ck.org
Cc: Alison Schofield <alison.schofield@...el.com>, lina@...hilina.net,
 zhang.lyra@...il.com, gerald.schaefer@...ux.ibm.com,
 vishal.l.verma@...el.com, dave.jiang@...el.com, logang@...tatee.com,
 bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com,
 will@...nel.org, mpe@...erman.id.au, npiggin@...il.com,
 dave.hansen@...ux.intel.com, ira.weiny@...el.com, willy@...radead.org,
 djwong@...nel.org, tytso@....edu, linmiaohe@...wei.com, peterx@...hat.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 david@...morbit.com, chenhuacai@...nel.org, kernel@...0n.name,
 loongarch@...ts.linux.dev
Subject: Re: [PATCH v7 13/20] mm/memory: Add vmf_insert_page_mkwrite()

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@...dia.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@...hat.com>

-- 
Cheers,

David / dhildenb