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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 Subject: Re: [PATCH 0/2] mm/userfaultfd: recheck WP registration in the hugetlb UFFDIO_COPY retry Message-ID: References: <20261029221129.89068-1-azpijr@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261029221129.89068-1-azpijr@gmail.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9FC64A0003 X-Stat-Signature: jpcd719hnjg7iyinthfjcgkhb45mab4e X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793438424-241485 X-HE-Meta: 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 PPOWC/x3 z5DYpw3ZM+7hzYWPJGbEqOM9DjF39nlIkHHl/7oNRJUhCDGuTsY7VXm/nVdwJiTl2PHbJUkkVhhZk6rOlf/ORY2MdJhL9cda/UX3TKXof9Hxh0AFQSPX9sB1e2/N7rikCXBRN9u/4lw+owNX3CnbEeiiI9queWIohb0zj6zXz+9OzanuYG+zDta6hrr1sPds7B7BJpaIcGXy5VLyyT7fFCqQFWOnuxwsl1CgOyNoeD8las9NEIO7FK4U6qCJUY765G3LCFlQ8h7vj8JKSkxwDevNFOdEG3sN9f+el7Zf5ynGLUHZf9DHnAgY/t8IhY2GZ0KpFCuA/t8q+/4c= 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 11:11:00PM +0100, Jose A. Perez de Azpillaga wrote: > The urgent fixes made hugetlb_fault() tolerate uffd bits left in VMAs > that are no longer registered for them, and asked for follow-ups that > remove the sources [1]. This is one: a hugetlb UFFDIO_COPY_MODE_WP copy > that has to fault in its source page doesn't recheck the WP registration > before retrying, so re-registering the range without WP in that window > leaves a uffd-wp PTE behind. > > Patch 1 adds the check the non-hugetlb retry already gets from > mfill_get_vma(). Patch 2 adds a uffd-unit-tests case for it, which fails > on hugetlb without patch 1. > > Question: > > - The non-hugetlb retry compares the whole mfill_retry_state. hugetlb > copies into a freshly allocated folio, so only WP seemed to matter > there. Mike, would you rather have the full comparison on both paths? Let's keep things simple and easily backportable :) Since hugetlb does not leave a folio from the original VMA behind there's no inconsistency we need to worry about. > The other source 6/10 of [1] mentions, UFFDIO_COPY in MODE_WP racing > with UFFDIO_UNREGISTER [2], is closed by "mm/userfaultfd: write-lock the > VMA before waking waiters when unregistering" [3]. > > Based on mm-unstable. > > Tested on x86_64 in QEMU. > > [1] https://lore.kernel.org/20261015-urgent_fixes-v1-0-42796911043b@kernel.org > [2] https://lore.kernel.org/20261015-urgent_fixes-v1-6-42796911043b@kernel.org > [3] https://lore.kernel.org/20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org (v1, now 23/47 in v2) > > Jose A. Perez de Azpillaga (2): > mm/userfaultfd: recheck WP registration in the hugetlb UFFDIO_COPY > retry > selftests/mm: add a uffd test for re-registering during UFFDIO_COPY > > mm/userfaultfd.c | 4 + > tools/testing/selftests/mm/uffd-unit-tests.c | 105 +++++++++++++++++++ > 2 files changed, 109 insertions(+) > > > base-commit: 24d45a1475dd4c671feb1df705f67ef2fc293969 > -- > 2.55.0 > -- Sincerely yours, Mike.