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Wed, 11 Nov 2026 14:12:26 -0500 (EST) Date: Wed, 11 Nov 2026 19:12:25 +0000 From: Kiryl Shutsemau To: Tal Zussman Cc: Andrew Morton , Mike Rapoport , Peter Xu , James Houghton , Andrea Arcangeli , Suren Baghdasaryan , Balbir Singh , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Andrei Vagin , Stephen Rothwell , Arnd Bergmann , Muhammad Usama Anjum , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Chris Down , Muchun Song , Oscar Salvador , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , Michal Hocko , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 06/12] mm/huge_memory: build the moved huge zero PMD from the destination VMA Message-ID: References: <20261111-uffd-state-fixes-v1-0-00713d368976@columbia.edu> <20261111-uffd-state-fixes-v1-6-00713d368976@columbia.edu> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261111-uffd-state-fixes-v1-6-00713d368976@columbia.edu> X-Rspamd-Queue-Id: 41EB710000D X-Rspamd-Server: rspam12 X-Stat-Signature: gmk8dtwnpiry18dsahyah366o48upjaq 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_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794424359-331999 X-HE-Meta: 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 DYR0wQZ4 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 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 On Wed, Nov 11, 2026 at 12:55:14PM -0500, Tal Zussman wrote: > move_pages_huge_pmd() builds the destination PMD for the huge zero page > by copying the source PMD and clearing its uffd bit, so the destination > keeps the protection of the source. > > A source VMA registered for RWP can map the huge zero page with a > PAGE_NONE PMD, and UFFDIO_MOVE does not check how the source is > registered. The destination then gets a PAGE_NONE PMD without the uffd > bit, although nothing asked for that in the destination VMA. > > The next access fixes it up through the NUMA hinting fault path. Until > then, the first access to the destination takes a spurious fault and GUP > has to take the fault path. The impact on userspace is small. > > The moved entry must have the protection of the destination VMA. To fix > it, build the entry from the vm_page_prot of the destination VMA, as > move_zeropage_pte() does for the small zero page, and keep marking it > soft-dirty. A destination VMA registered for RWP still gets its PMD > re-armed afterwards. > > Fixes: 763f43865fc4 ("mm: preserve RWP marker across PTE rewrites") > Signed-off-by: Tal Zussman Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov