From: Mike Rapoport <rppt@kernel.org>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linuxfoundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Oleg Nesterov <oleg@redhat.com>, Peter Xu <peterx@redhat.com>,
vova tokarev <vladimirelitokarev@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
stable@vger.kernel.org
Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs
Date: Thu, 18 Jun 2026 12:21:52 +0300 [thread overview]
Message-ID: <ajO4sLq2UBciSgOn@kernel.org> (raw)
In-Reply-To: <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org>
On Thu, Jun 18, 2026 at 10:47:19AM +0200, David Hildenbrand (Arm) wrote:
> On 6/18/26 10:43, Mike Rapoport wrote:
> > On Thu, Jun 18, 2026 at 11:34:12AM +0300, Mike Rapoport wrote:
> >> On Thu, Jun 18, 2026 at 10:19:17AM +0200, David Hildenbrand (Arm) wrote:
> >>>
> >>> I'm sure you considered VM_SPECIAL, which additionally includes VM_DONTEXPAND.
> >>>
> >>> Would that be better, or what was the reason to allow VM_DONTEXPAND?
> >>
> >> By itself VM_DONTEXPAND won't matter, as uffd can't resize a VMA.
> >> But thinking more about it, it's better to make vma_can_userfault() more
> >> restrictive and just use VM_SPECIAL.
> >
> > Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with
> > hugetlb.
>
> It would probably be cleaner to just allow hugetlb, and then check for
> VM_SPECIAL if not hugetlb.
Cleaner in what sense?
Will be uglier for sure, just take a look at vma_can_userfault().
> --
> Cheers,
> David
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2026-06-18 9:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-17 19:40 [PATCH] userfaultfd: prevent registration of special VMAs Mike Rapoport
2026-06-18 8:19 ` David Hildenbrand (Arm)
2026-06-18 8:34 ` Mike Rapoport
2026-06-18 8:43 ` Mike Rapoport
2026-06-18 8:47 ` David Hildenbrand (Arm)
2026-06-18 9:21 ` Mike Rapoport [this message]
2026-06-18 9:25 ` David Hildenbrand (Arm)
2026-06-18 9:35 ` Mike Rapoport
2026-06-18 9:37 ` David Hildenbrand (Arm)
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