Re: [PATCH 2/3] mm: secretmem: convert to .mmap_prepare() hook

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Fri, May 09, 2025 at 11:45:16AM +0200, David Hildenbrand wrote:
> On 07.05.25 13:03, Lorenzo Stoakes wrote:
> > Secretmem has a simple .mmap() hook which is easily converted to the new
> > .mmap_prepare() callback.
> >
> > Importantly, it's a rare instance of an driver that manipulates a VMA which
> > is mergeable (that is, not a VM_SPECIAL mapping) while also adjusting VMA
> > flags which may adjust mergeability, meaning the retry merge logic might
> > impact whether or not the VMA is merged.
> >
> > By using .mmap_prepare() there's no longer any need to retry the merge
> > later as we can simply set the correct flags from the start.
> >
> > This change therefore allows us to remove the retry merge logic in a
> > subsequent commit.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > ---
> >   mm/secretmem.c | 14 +++++++-------
> >   1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/secretmem.c b/mm/secretmem.c
> > index 1b0a214ee558..f98cf3654974 100644
> > --- a/mm/secretmem.c
> > +++ b/mm/secretmem.c
> > @@ -120,18 +120,18 @@ static int secretmem_release(struct inode *inode, struct file *file)
> >   	return 0;
> >   }
> > -static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
> > +static int secretmem_mmap_prepare(struct vm_area_desc *desc)
> >   {
> > -	unsigned long len = vma->vm_end - vma->vm_start;
> > +	unsigned long len = desc->end - desc->start;
>
> I'd have marked that const while touching it.

Will fix up on respin.

>
> > -	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> > +	if ((desc->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> >   		return -EINVAL;
> > -	if (!mlock_future_ok(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
> > +	if (!mlock_future_ok(desc->mm, desc->vm_flags | VM_LOCKED, len))
> >   		return -EAGAIN;
> > -	vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
> > -	vma->vm_ops = &secretmem_vm_ops;
> > +	desc->vm_flags |= VM_LOCKED | VM_DONTDUMP;
> > +	desc->vm_ops = &secretmem_vm_ops;
>
> Yeah, that looks much better.
>
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks!

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