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Perez de Azpillaga" Cc: Andrew Morton , David Hildenbrand , Shuah Khan , Peter Xu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Muchun Song , Oscar Salvador , stable@vger.kernel.org Subject: Re: [PATCH 1/2] mm/userfaultfd: recheck WP registration in the hugetlb UFFDIO_COPY retry Message-ID: References: <20261029221129.89068-1-azpijr@gmail.com> <20261029221129.89068-2-azpijr@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261029221129.89068-2-azpijr@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 44CFB40002 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: 7jayrmckn6ozmg5w74qjkk5uez44t9ag X-HE-Tag: 1793438704-908277 X-HE-Meta: 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 yV5qrkcr yFZnlynkEVb73phcAh81NZJJkMFEixP4x1acDl5M+hi4zJDE4gJGzSatX37YyhnfzD+LiSFShft3uHFs7luBfvO4qVXaEAt/TCQC5RDWM6FdAe3ZORntwDdQ+jQpJqKTayJU0wB3dGT7dQ+wpWrAanO9JnOm2RGFMz3FPzSZVOh6SLbUdalIv8RfGUoG3hMfao9iqtmn2NmEOtM4fFSDqO7nGDSQp/2zIHwkuVnUqDgJcM0zAmWwAD6/D5Sa4WE6hevefm7MRPanCCxgFbc8E7UZr8OofomD035enTULjQMh8a7MUm3zk/s850E/hnmTnSu+PRdG2IqKu4FukEWuKnzcXHq/fj0p4DLu3 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Jose, On Thu, Oct 29, 2026 at 11:11:01PM +0100, Jose A. Perez de Azpillaga wrote: > mfill_atomic_hugetlb() drops its locks to copy the source page with page > faults enabled and then looks the VMA up again. The retry doesn't check > that the VMA is still registered for WP, so if the range is re-registered > without WP in that window, a UFFDIO_COPY_MODE_WP copy installs a uffd-wp > PTE in a VMA without VM_UFFD_WP. That is one of the leftover uffd bits > hugetlb_fault() has to tolerate. The "leftover" sentence will be confusing for future readers > The non-hugetlb retry goes through mfill_get_vma() again and fails with > -EINVAL. Do the same check in the hugetlb retry. No need to reference non-hugetlb path, just describe the added check. > Fixes: 6041c6917903 ("mm/hugetlb: take care of UFFDIO_COPY_MODE_WP") > Cc: stable@vger.kernel.org > Signed-off-by: Jose A. Perez de Azpillaga With those fixed: Reviewed-by: Mike Rapoport (Microsoft) > --- > mm/userfaultfd.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 3b71712edab4..a70ecfc8a998 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -810,6 +810,10 @@ static __always_inline ssize_t mfill_atomic_hugetlb( > if (vma_hpagesize != vma_kernel_pagesize(dst_vma)) > goto out_unlock_vma; > > + /* The range may have been re-registered without WP meanwhile. */ > + if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) > + goto out_unlock_vma; > + > /* > * If memory mappings are changing because of non-cooperative > * operation (e.g. mremap) running in parallel, bail out and > -- > 2.55.0 > -- Sincerely yours, Mike.