Re: [RFC PATCH v2 2/3] mm: secretmem: convert to .mmap_prepare() hook

[Mike Rapoport <rppt@kernel.org>]

On Thu, May 01, 2025 at 06:25:28PM +0100, 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;
>  
> -	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;
>  
>  	return 0;
>  }
> @@ -143,7 +143,7 @@ bool vma_is_secretmem(struct vm_area_struct *vma)
>  
>  static const struct file_operations secretmem_fops = {
>  	.release	= secretmem_release,
> -	.mmap		= secretmem_mmap,
> +	.mmap_prepare	= secretmem_mmap_prepare,
>  };
>  
>  static int secretmem_migrate_folio(struct address_space *mapping,
> -- 
> 2.49.0
> 

-- 
Sincerely yours,
Mike.