linux-kernel - Re: [PATCH 2/5] mm/mseal: move madvise() logic to mm/madvise.c

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Message-ID: <26a1fc6d-d0c5-4f5c-9669-0593a9a6b59c@lucifer.local>
Date: Mon, 14 Jul 2025 16:37:33 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Pedro Falcato <pfalcato@...e.de>
Cc: David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Jeff Xu <jeffxu@...omium.org>
Subject: Re: [PATCH 2/5] mm/mseal: move madvise() logic to mm/madvise.c

On Mon, Jul 14, 2025 at 04:31:59PM +0100, Pedro Falcato wrote:
> On Mon, Jul 14, 2025 at 05:03:03PM +0200, David Hildenbrand wrote:
> > [...]
> >
> > But now I wonder, why is it okay to discard anon pages in a MAP_PRIVATE file
> > mapping?
>
> IIRC this was originally suggested by Linus, on one of the versions introducing
> mseal. But the gist is that discarding pages is okay if you could already zero
> them manually, using e.g memset. Hence the writeability checks.

Right, and if it's read-only and MAP_PRIVATE it doesn't really matter. In which
case we needn't worry.

I wonder if we need to check for VM_MAYWRITE though...

>
> --
> Pedro