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Wed, 28 Oct 2026 13:12:28 +0000 X-Mizu-Trace-ID: db747fb4ed3da529 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kees@kernel.org, peterz@infradead.org, jannh@google.com, pfalcato@suse.de, hughd@google.com, pasha.tatashin@soleen.com, pratyush@kernel.org, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, lance.yang@linux.dev, riel@surriel.com, harry@kernel.org, apopple@nvidia.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, jhubbard@nvidia.com, peterx@redhat.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, osalvador@suse.de, minchan@kernel.org, muchun.song@linux.dev, xu.xin@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, youngjun.park@lge.com, gourry@gourry.net, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, jgg@ziepe.ca, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 11/46] mm/huge_memory: properly handle refcounted PUD mappings on fork Date: Wed, 28 Oct 2026 21:12:21 +0800 Message-ID: <20261028131221.42261-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261027-fixes_core-v1-11-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-11-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 235B540007 X-Stat-Signature: ubucwymufkmznwyckx6m1hog8tiresz7 X-Rspam-User: X-Spam-Status: No, score=-13.8 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, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-HE-Tag: 1793193150-650270 X-HE-Meta: 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 QJj7dsLb 6RY49no5Ki5e+y4dsFw7SmxedHux6Xu/dEQ4L/lnS6q7bp1pvli+/ErQk/fR2WPWjXWOlTuzlrgDt88y5ELwbRsZ7Yq3tC95+vkkPoe3B1dQVKfdGj5tKsioNT5GhgCmFikM5AKJV/jYFt407zMquiyN3dz45+azKHGM6T5aYjDiaUQniDSDvDn+KX4UhMUzoDDW5S7VDSdjSk1eCiseYV3tYbiHgKnx9x1AZWejus4RIxliNGWjVundn4mtmRaaNKsCNJC9+jB6XwBSRM+zwqF3RPJzj+ssEBMPmWO5PHjzPJclmrw7V4GLX3vBgbdYOQG2M5c7TLrJjgRvEdZw3v8mw6SZnBUEXTJBhAuUkBitYp60Ht1eyziHm854Ufv0qPCyE 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 Tue, Oct 27, 2026 at 12:17:31AM +0100, David Hildenbrand (Arm) wrote: >copy_huge_pud() copies device-DAX entries without taking a folio reference >or updating mapcounts and the child's RSS. > >For example, MADV_GUARD_INSTALL sets VM_MAYBE_GUARD on a device-DAX VMA, >forcing copy_page_range() to traverse the whole VMA on fork. Any remaining >huge PUDs are then copied without accounting for the new mappings. >Unmapping them in the child decrements accounting that was never added. > >Use vm_normal_page_pud() to identify refcounted mappings. Take a folio >reference and add the child's PUD rmap and RSS accounting before installing >the copied entry. Pass src and dst VMAs consistently instead of src and >dst MM. Move the TODO. > >Fixes: aed877c2b4257 ("device/dax: properly refcount device dax pages when mapping") >Cc: stable@vger.kernel.org >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang