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bh=mHGE9nXbxuB8GQ9t8LPv8LBGWevl1d8ukNIHXAQHhiw=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793193149; v=1; x=1793797949; b=fGEzUaEr8w61+lFUJkekZQi4IchHFI1oGuTpYnywD4uq7NYgtMIB4KLVEQTX9tu3L0+pzd7X uJGPjUqkyRJ7/LGJdP9Yu5YYeiFDulf+ETYGKM/YTzW7aaDU7ISl7xwUjOV6DayGav6115xQZ23 2+9Gu5zJq6L2EXkbbQRvZNpM= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id db747fb4ed3da529; 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-Mailing-List: linux-kernel@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=UTF-8 Content-Transfer-Encoding: 8bit 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