linux-kernel - Re: [PATCH v4 4/5] mm/mseal: simplify and rename VMA gap check

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Message-ID: <CABi2SkVRmuRp459g0RBwyTbd5dACwe6AiHrpxYuPXj41MxHp+A@mail.gmail.com>
Date: Fri, 25 Jul 2025 11:09:13 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, 
	David Hildenbrand <david@...hat.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, 
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v4 4/5] mm/mseal: simplify and rename VMA gap check

Hi Lorenzo

On Fri, Jul 25, 2025 at 10:43 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> On Fri, Jul 25, 2025 at 10:30:08AM -0700, Jeff Xu wrote:
> > Hi Lorenzo,
> >
> > On Fri, Jul 25, 2025 at 1:30 AM Lorenzo Stoakes
> > <lorenzo.stoakes@...cle.com> 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().
> > >
> > Thanks for keeping the comments.
>
> You're welcome.
>
> >
> > In the prior version of this patch, I requested that we keep the
> > check_mm_seal()  and its comments. And this version keeps the comments
> > but removes the check_mm_seal() name.
>
> I didn't catch that being your request.
>
> >
> > As I said, check_mm_seal() with its comments is a contract for
> > entry-check for mseal().  My understanding is that you are going to
> > move range_contains_unmapped() to vma.c. When that happens, mseal()
> > will lose this entry-check contract.
>
> This is just bizarre.
>
> Code doesn't stop working if you put it in another function.
>
> And you're now reviewing me for stuff I haven't done? :P
>
> >
> > Contact is a great way to hide implementation details. Could you
> > please keep check_mm_seal() in mseal.c and create
> > range_contains_unmapped() in vma.c. Then you can refactor as needed.
>
> Wait what?
>
> OK maybe now I see what you mean, you want a function that just wraps
> range_contains_unmapped() with a comment explaining the 'contract'.
>
Yes. You can view it that way from an implementation point of view.

Contract mainly serves as a way to help design and abstract the code.

> range_contains_unmapped() enforces your required contract and the comments
> make it extremely explicit, so this is not a reasonable request, sorry.

Technically, this contract belongs to mseal, but if you have strong
opinions on this, that's fine, as long as range_contains_unmapped()
doesn't accidentally remove those comments in the future, which I'm
sure you won't.

Acked-by: Jeff Xu <jeffxu@...omium.org>

Thanks and regards,
-Jeff