linux-kernel - Re: [PATCH v2 03/16] mm: add vma_desc_size(), vma_desc

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Message-ID: <17b6846e-d06e-4a2f-9104-17b147cafc7d@lucifer.local>
Date: Mon, 15 Sep 2025 11:12:51 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>,
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Subject: Re: [PATCH v2 03/16] mm: add vma_desc_size(), vma_desc_pages()
 helpers

On Fri, Sep 12, 2025 at 07:56:46PM +0200, David Hildenbrand wrote:
> On 10.09.25 22:21, Lorenzo Stoakes wrote:
> > It's useful to be able to determine the size of a VMA descriptor range used
> > on f_op->mmap_prepare, expressed both in bytes and pages, so add helpers
> > for both and update code that could make use of it to do so.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > ---
> >   fs/ntfs3/file.c    |  2 +-
> >   include/linux/mm.h | 10 ++++++++++
> >   mm/secretmem.c     |  2 +-
> >   3 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
> > index c1ece707b195..86eb88f62714 100644
> > --- a/fs/ntfs3/file.c
> > +++ b/fs/ntfs3/file.c
> > @@ -304,7 +304,7 @@ static int ntfs_file_mmap_prepare(struct vm_area_desc *desc)
> >   	if (rw) {
> >   		u64 to = min_t(loff_t, i_size_read(inode),
> > -			       from + desc->end - desc->start);
> > +			       from + vma_desc_size(desc));
> >   		if (is_sparsed(ni)) {
> >   			/* Allocate clusters for rw map. */
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 892fe5dbf9de..0b97589aec6d 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3572,6 +3572,16 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
> >   	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> >   }
> > +static inline unsigned long vma_desc_size(struct vm_area_desc *desc)
> > +{
> > +	return desc->end - desc->start;
> > +}
> > +
> > +static inline unsigned long vma_desc_pages(struct vm_area_desc *desc)
> > +{
> > +	return vma_desc_size(desc) >> PAGE_SHIFT;
> > +}
>
> Should parameters in both functions be const * ?

Can do, will fix up if respin.

>
> > +
> >   /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
> >   static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
> >   				unsigned long vm_start, unsigned long vm_end)
> > diff --git a/mm/secretmem.c b/mm/secretmem.c
> > index 60137305bc20..62066ddb1e9c 100644
> > --- a/mm/secretmem.c
> > +++ b/mm/secretmem.c
> > @@ -120,7 +120,7 @@ static int secretmem_release(struct inode *inode, struct file *file)
> >   static int secretmem_mmap_prepare(struct vm_area_desc *desc)
> >   {
> > -	const unsigned long len = desc->end - desc->start;
> > +	const unsigned long len = vma_desc_size(desc);
> >   	if ((desc->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> >   		return -EINVAL;
>
> Acked-by: David Hildenbrand <david@...hat.com>

Thanks!

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo