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Wed, 28 Oct 2026 13:05:05 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 7Zm8CQHz4WrpIAAAD6G6ig (envelope-from ); Wed, 28 Oct 2026 13:05:05 +0000 Date: Wed, 28 Oct 2026 13:05:03 +0000 From: Pedro Falcato To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , 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 Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-11-6f74bec9a5bb@kernel.org> X-Mailing-List: linux-arch@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=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-11-6f74bec9a5bb@kernel.org> X-Spamd-Result: default: False [-11.80 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; TAGGED_RCPT(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[linux-foundation.org,cmpxchg.org,kernel.org,linux.dev,tencent.com,google.com,linux.alibaba.com,infradead.org,suse.com,soleen.com,suse.cz,nvidia.com,surriel.com,arm.com,intel.com,redhat.com,gmail.com,suse.de,huaweicloud.com,lge.com,gourry.net,sk.com,ziepe.ca,kvack.org,vger.kernel.org,lists.infradead.org]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_GT_50(0.00)[64]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Score: -11.80 X-Spam-Level: X-Spam-Flag: NO 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: Pedro Falcato -- Pedro