linux-kernel - Re: [PATCH 2/3] mm: secretmem: convert to .mmap

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Message-ID: <708b6b1b-54a0-43b8-b6ec-a2dbb089d432@redhat.com>
Date: Fri, 9 May 2025 11:45:16 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 2/3] mm: secretmem: convert to .mmap_prepare() hook

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@...cle.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.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.

>   
> -	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@...hat.com>

-- 
Cheers,

David / dhildenb