linux-kernel - Re: [PATCH v2 1/4] mm: Introduce vm_uffd

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Message-ID: <7cccbceb-b833-4a21-bdc4-1ff9d1d6c14f@lucifer.local>
Date: Thu, 18 Sep 2025 18:45:28 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Nikita Kalyazin <kalyazin@...zon.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Muchun Song <muchun.song@...ux.dev>, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        James Houghton <jthoughton@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Ujwal Kundur <ujwal.kundur@...il.com>
Subject: Re: [PATCH v2 1/4] mm: Introduce vm_uffd_ops API

On Thu, Sep 18, 2025 at 06:15:41PM +0100, Nikita Kalyazin wrote:
> The other patches it I was building on top were mmap support in guest_memfd
> [4], which is currently merged in kvm/next, and also part of [3].
>
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/david/linux.git/tree/virt/kvm/guest_memfd.c?id=911634bac3107b237dcd8fdcb6ac91a22741cbe7#n347
> [4] https://lore.kernel.org/kvm/20250729225455.670324-1-seanjc@google.com

Note that the mmap implementation is changing to mmap_prepare. It's the
case in point example of where we exposed an internal mm object (VMA) and
experienced significant issues including embargoed critical zero-day
security reports as a result.

I took a quick look at [3] and it seems you're using it in a totally normal
way which is completely fine, however, and it'll be very easily convertible
to mmap_prepare.

Cheers, Lorenzo