linux-kernel - Re: [PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check

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Message-ID: <9845f6f3-6265-49e9-8eba-5855b2b5f90e@redhat.com>
Date: Wed, 16 Jul 2025 15:38:51 +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>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Jeff Xu <jeffxu@...omium.org>
Subject: Re: [PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check

On 15.07.25 15:37, Lorenzo Stoakes wrote:
> The check_mm_seal() function is doing something general - checking whether
> a range contains only VMAs (or rather that it does NOT contain any unmapped
> regions).
> 
> So rename this function to range_contains_unmapped().
> 
> Additionally simplify the logic, we are simply checking whether the last
> vma->vm_end has either a VMA starting after it or ends before the end
> parameter.
> 
> This check is rather dubious, so it is sensible to keep it local to
> mm/mseal.c as at a later stage it may be removed, and we don't want any
> other mm code to perform such a check.
> 
> No functional change intended.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
>   mm/mseal.c | 56 ++++++++++++++++++++----------------------------------
>   1 file changed, 21 insertions(+), 35 deletions(-)
> 
> diff --git a/mm/mseal.c b/mm/mseal.c
> index adbcc65e9660..794d1043a706 100644
> --- a/mm/mseal.c
> +++ b/mm/mseal.c
> @@ -37,34 +37,6 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
>   	return ret;
>   }
> 
> -/*
> - * Check for do_mseal:
> - * 1> start is part of a valid vma.
> - * 2> end is part of a valid vma.
> - * 3> No gap (unallocated address) between start and end.
> - * 4> map is sealable.
> - */
> -static int check_mm_seal(unsigned long start, unsigned long end)
> -{
> -	struct vm_area_struct *vma;
> -	unsigned long nstart = start;
> -	VMA_ITERATOR(vmi, current->mm, start);
> -
> -	/* going through each vma to check. */
> -	for_each_vma_range(vmi, vma, end) {
> -		if (vma->vm_start > nstart)
> -			/* unallocated memory found. */
> -			return -ENOMEM;
> -
> -		if (vma->vm_end >= end)
> -			return 0;
> -
> -		nstart = vma->vm_end;
> -	}
> -
> -	return -ENOMEM;
> -}
> -
>   /*
>    * Apply sealing.
>    */
> @@ -102,6 +74,24 @@ static int apply_mm_seal(unsigned long start, unsigned long end)
>   	return 0;
>   }
> 
> +/* Does the [start, end) range contain any unmapped memory? */
> +static bool range_contains_unmapped(struct mm_struct *mm,
> +		unsigned long start, unsigned long end)
> +{
> +	struct vm_area_struct *vma;
> +	unsigned long prev_end = start;
> +	VMA_ITERATOR(vmi, current->mm, start);
> +
> +	for_each_vma_range(vmi, vma, end) {
> +		if (vma->vm_start > prev_end)
> +			return true;
> +
> +		prev_end = vma->vm_end;
> +	}
> +
> +	return prev_end < end;
> +}
> +

Probably better to not ... move the function in the same file? Then, we 
can se the actual diff of changes easily.

-- 
Cheers,

David / dhildenb