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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-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261029221129.89068-2-azpijr@gmail.com> 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.