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bh=r/y28Pr8KNBr61CZIB3z7msn3ARAQOG25oOo8bDyEqs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793621962; v=1; x=1794226762; b=Z6X9Wt1f2OM0mk9Cvw5ZsBYTsSsI5PkwaBYJjVaRrHKRsTE9x/ymuRWOcLnrF28+pJweuNV7 6EzFPwGVjc92CRJwXYeA37ONO25xqpbqAElMy37M/9RJ7oZUyP837HGQFBUQd7QRrP3u8yb4+GD 5HLS9jSoxykzaPBgfV1a8xbo= X-Envelope-To: linux-arch@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id c966688054ce713b; Mon, 02 Nov 2026 12:19:21 +0000 X-Mizu-Trace-ID: c966688054ce713b 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, usama.anjum@arm.com Subject: Re: [PATCH v3 31/47] mm/mremap: recheck PUDs under the page table lock Date: Mon, 2 Nov 2026 20:19:14 +0800 Message-ID: <20261102121914.69229-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261031-fixes_core-v3-31-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-31-d6437171ecc3@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=UTF-8 Content-Transfer-Encoding: 8bit On Sat, Oct 31, 2026 at 10:40:00AM +0100, David Hildenbrand (Arm) wrote: >Once get_old_pud() is fixed to accept PUD leaves, unmap_mapping_range() can >clear a leaf between the lookup and the move. Holding mmap_lock in write >mode does not prevent this. > >If the zap happens before move_page_tables() tests the entry, an empty >PUD can reach move_normal_pud(), where pud_populate() turns it into a >present page table entry. If it happens after the test, move_huge_pud() >can instead try to move an empty entry, triggering CONFIG_DEBUG_VM >warnings on powerpc. > >Recheck the source under the page table lock in both helpers. Treat an >empty source in move_normal_pud() as a completed move, and use >__pud_trans_huge_lock() in move_huge_pud(). > >In the future we should likely have the code lookup a PUD/PMD lockless >once, instead of multiple times, because one of the problematic bits >here is the: > > pud_trans_huge(*old_pud) > >Fixes: 0881ace292b6 ("mm/mremap: use pmd/pud_poplulate to update page table entries") >Cc: stable@vger.kernel.org >Reviewed-by: Lorenzo Stoakes (ARM) >Reviewed-by: Pedro Falcato >Tested-by: Muhammad Usama Anjum >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang