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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jonathan Corbet , Shuah Khan , Randy Dunlap , Peter Xu , Breno Leitao , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerd Hoffmann , linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, stable@kernel.org, Chris Mason Content-Transfer-Encoding: quoted-printable Message-Id: <9FFF0EF2-A99A-4448-9CA3-50E1733D6232@linux.dev> References: <20261028-fixes_hugetlb-v1-0-a0a033db180f@kernel.org> <20261028-fixes_hugetlb-v1-6-a0a033db180f@kernel.org> To: "David Hildenbrand (Arm)" X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 632AA40004 X-Stat-Signature: t3qfnsintrxmswow9qa49fhp1jedoar9 X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,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: 1793352051-501363 X-HE-Meta: U2FsdGVkX1864F2OGWGHL0gmqDm8hPCjBqHHYS4tfZqpVz9znE0jq77Jru/XY+ispU4nwwmIHuboj50bpUn1y9TnXFc+9bIqTe7MAp6pUHecpN2ccbpuI2x2HUZ7cAc5MOh2UwX1oxBMJQ6/8BL7NYP5ySZjyfEGNUlgCu/9+w/K7Uimxp19PF2W0/fKE6Vx+j/IGPiMdiXotmtffdA0Vzy9DU4PE69tgRAKHUS9sjepnNo9QjXfFOQCmtaoMaJmgdW4btVLtCkrc33BRFY0zlJOPl67X9DIfKqvNK08PEdF+xbADTmtr9r6Qtf+Mj6tid/uf6TiUzstG3DO9sQzGfSkg10gs+HoB8xcoJgJEwmuf5i56Yc65KJOfv6IX5DzXB5HhPJmjQesHgwCAPzPQ4wBt+vmRv2Mk1aY0HJnS7xb7wt7KdGyrorJ+4WODn0gu7Gh2JRKy69KgjC/L1jmY5FqWVKLYeq+NLqw/aMzB2nCDbdER2/gzjck3klSrYHGt5jYVW5HMTHLwTcd1PRRCsI9/VjQLTi0w9QEH+2hpGSUjftwRxyoUpJAoivKqgdhm6abruzkXT1jdETnNvBu7FnP8DKwu5/TrxQphF/BWaVDyvovK5hp8CIE2hBlixN2xKG7Ab2YG3+kkPvZzMV/pWGJdl8PuCNz8Q5o7cysQwlPhAMc3Bus1S32I9Fw1K3SzH7JmbrXn216Mr4twq5bJQjDH0S1F1NXTH6F51268qqBbt9N2ynSVessERdakmurRisQETwujwBvMFWdns6qY4vAQaHyKkxZJv+oZOZeQ7MeVLuPP6Z3FZIKiG0mfYhwZ6sUqlDDupBezPPCd5YY0j4QNTT2nu+lYoonWyFKxII/kQeFUa1cCLD3OhE5KoyoXEON4cWTQtvEtpON60bP6pDH7yh98tA2++8T9FSKzRbAuCDMqaxMVAUNYqfQwnBGoyzfsH89a8XJ/TnDmfG sZ2Sq17d ymIJCth3ABEoZ73JGNPNCN6sNdTuAi9twSyEGMWTWHRBByebRVvVgZUla1/nfVEM+EhfpSCK53FBdRLnZe5n+up0bkWPCYhl7rZ6+O3BdCZWqFUyVByz7vJGJ8swt4NUFygiormDbhf6CvJSSRipiW0BEGt5J9K/RGsKj9tYR6dcMxwy7SA9tumjOeDM67KIJU36dIT5oup4VSSEhR9VzQZDeNI4pkm41YEtckoE6ssBpe2xmfiwzZiNkCj3D0EFeYy/tSm3yANMSMC3wgsbPCP7aJ0S4p2YboS4PqRVJLVyiWItXWJe/a4KJas3HeEoqFfCp6kYkh4hFkdu4UrhO9RxdperWOtEO7rx92sQln17lxF/o/kMn1mzyOXCBqqQLHBXf3cQ25BNRXgXnhsdS55mJRw== 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 Oct 29, 2026, at 04:13, David Hildenbrand (Arm) = wrote: >=20 > Migration of anon hugetlb folios walks the anon_vma, so the file's > i_mmap_rwsem does not serialize it against move_hugetlb_page_tables(). >=20 > There are various issues with that. Most importantly, move_huge_pte() > releases both page table locks before the TLB is flushed. Migration = can > then find the destination entry and finish migration, reusing the old > folio while the TLB still has entries cached. >=20 > Hold the anon_vma write lock across the move and the final TLB flush. > This also prevents concurrent rmap walks from missing entries moved > during rollback. >=20 > When we must allocate a destination page table, flush the TLB before > dropping the anon_vma lock, then reacquire it after allocation. >=20 > Dropping the lock only works around lockdep: hugetlb folios are not > reclaimed or migrated by allocation compaction, but their anon_vmas > share the lock class used by ordinary anonymous memory. Having a > separate lock class for hugetlb's anon_vma (like already done for > i_mmap_rwsem via hugetlbfs_i_mmap_rwsem_key) requires more thought. >=20 > There is a concern that this can block page migration of anonymous > folios quite a while ... which is not really different to what happens > to page-cache folios today. If ever a problem, we can temporarily > release the lock. >=20 > So let's keep it simple for now. Make sense. >=20 > It is a shame that hugetlb has to implement everything core-mm = implements > in a different way that just screams for problems. Yeah, nightmare in MM. >=20 > Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage = backed vma") > Cc: stable@kernel.org > Reported-by: Chris Mason > Signed-off-by: David Hildenbrand (Arm) Acked-by: Muchun Song Thanks.