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

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Message-ID: <d1fa842b-ba0b-4bb1-8d0b-cccaeedadf69@lucifer.local>
Date: Fri, 25 Jul 2025 19:15:30 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jeff Xu <jeffxu@...omium.org>
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

On Fri, Jul 25, 2025 at 11:09:13AM -0700, Jeff Xu wrote:
> Hi Lorenzo
>
> On Fri, Jul 25, 2025 at 10:43 AM Lorenzo Stoakes
> > 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.

Right sure, I sort of good the idea, I just think it's a bit OTT for this
check whose contract is already clearly stated in 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.

We won't change the semantics without a specific patch suggesting to do so,
which you and Kees will be cc'd on!

I care very much about making sure we get the mechanics of mseal() right,
so I'm not going to allow such changes unless we sensibly reach agreement
that it's the right way forward (i.e. the same obviously as if we chose to
_change_ a contract formulation using your approach).


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

Thanks, appreciated!

>
> Thanks and regards,
> -Jeff

Cheers, Lorenzo