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

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Message-ID: <74b92ce3-9e0e-4361-8117-7abda27f2dd4@redhat.com>
Date: Thu, 18 Sep 2025 19:53:46 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Nikita Kalyazin <kalyazin@...zon.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Mike Rapoport <rppt@...nel.org>, Peter Xu <peterx@...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 18.09.25 19:45, Lorenzo Stoakes wrote:
> 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.

Yes, we'll take care of that once it's (finally :D ) upstream!

Re Nikita: If we could just reuse fault() for userfaultfd purposes, that 
might actually be pretty nice.

-- 
Cheers

David / dhildenb