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

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Message-ID: <ca6af6bc-1c5b-47fc-a00b-11d46867b5e7@lucifer.local>
Date: Fri, 25 Jul 2025 18:43:36 +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 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'.

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