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Howlett" , Lorenzo Stoakes , Michael Bommarito , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/3] userfaultfd: refuse to __mfill_atomic_pte() for unsupported VMAs Message-ID: References: <20260527184751.4147364-1-rppt@kernel.org> <20260527184751.4147364-3-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: eickf3jbzh8fggqj1nfh65xhq9bcxxah X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D6CB780004 X-Rspam-User: X-HE-Tag: 1779953599-712298 X-HE-Meta: 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 j9Nw8xgw hJr32YRh/YsLMnjVLxhLEKFVZ+vbbeM6odu7p4o8pi6jSgqZth7Wsxv2fz+wP2nods/ksLtZx/EbT8jmeh6tJmjEWfsnaMYUq2c5lnrf5Tp109g39iUxmawOCq54h3iemNMceCUQlkWCNwm/t+ImJvHWcbW/+CdHdQzZ9KPy8jXAQEnh7sg2yVSxBkWeKpTqapF0/VoBjSs9OFmfznVtP009HCkml3tGTCYz2KJLBUCZKwnrvMWj30RHrOozaBhUag06Tj4UAk6AYM8+dJ3WzCWScYDVyZ1LS+urBVeSp5tvLAmWL+3W8tnJUiMaWlNuY/GdYm9q8R2BzlA/0CbVUcVHtRwPryMJw1LxLOI+WStm0W0TIWegSrTgx0N1DhVQTAzX67khTpo9IG4c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 27, 2026 at 08:09:01PM +0100, David CARLIER wrote: > Hi, > > just chiming it > > On Wed, 27 May 2026 at 19:48, Mike Rapoport wrote: > > > > From: "Mike Rapoport (Microsoft)" > > > > __mfill_atomic_pte() unconditionally dereferences ops because there is an > > assumption that VMAs that can undergo mfill_* operations are vetted on > > registration and must have valid vm_uffd_ops. > > > > Add a guard against potential bugs and make sure __mfill_atomic_pte() bails > > out if ops is NULL. > > > > Suggested-by: Lorenzo Stoakes > > Fixes: ad9ac3081332 ("userfaultfd: introduce vm_uffd_ops->alloc_folio()") > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > mm/userfaultfd.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index e5d2fb3ce2c1..2872c71bbf36 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -552,6 +552,11 @@ static int __mfill_atomic_pte(struct mfill_state *state, > > struct folio *folio; > > int ret; > > > > + if (!ops) { > > + VM_WARN_ONCE(1, "UFFDIO_COPY for unsupported VMA"); > > nit: Is the warning message a bit too specific ? i.e. Also handle > MFILL_ATOMIC_ZEROPAGE case. It handles ZEROPAGE case by actually copying a zeroed page there so in a sense it's still a copy. Differentiating COPY and ZEROPAGE here will add complexity that is not justified for a message that should be never printed. > > + return -EOPNOTSUPP; > > + } > > + > > folio = ops->alloc_folio(state->vma, state->dst_addr); > > if (!folio) > > return -ENOMEM; > > -- > > 2.53.0 > > > > Cheers. > -- Sincerely yours, Mike.