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

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Message-ID: <e657e16f-7929-4e2a-b0f7-8627979a8099@lucifer.local>
Date: Wed, 16 Jul 2025 16:01:15 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "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 Wed, Jul 16, 2025 at 03:38:51PM +0200, David Hildenbrand wrote:
> 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.

Sure, will respin with that.

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