From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.173 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793621966; b=NFsnSPTpT/C3bURk+PNyLICp/ACxbT7eP/yBKTzKl9vSR9VceCECrXjtjOAmTEEZODcr 9jckSxNP03PCvSbicrjnbYnQQCsKhESte3bgbxBWwKNMEy38NzOJ3uj9oOYMAEQYcIPxb HfT3t9Ksd2dgDFP6JdPYuQNbL6d5vYFXJerBZ1R98xVxtgqo4WG9VYSB1RSdlCu1C8JPj OlOGUfYT1CfXtYT/tW8v+rfNylOTpaIkrGV8q7s0JLt70fjpPOi/m065ggJ6E4D83G0iD Ve1Mf/+qKb0Jmtan2qm6j1XmoRGsMIC9vBAWuvUz+O1r4k0yBY5eLEDgWhzLVGaPVTw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793621966; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=7aamrL1eeNrbIdMSN+jaXpW6b7pg64KUgg9/NR7r4M8=; b=vkPWPbEbmN+nXVo13bXF2pISs7IX2kweK5vwKJNX/qqjGBgjK8OjJGYEz7jHriHhX6ms V4ZbcqXXa4m1pJyCEfnFynpGcYWrWRBWTpdWFzumpkjYiAAr2FxSYh2gWWhFVPSC8jscp t9prkIfES/4UKPh5a1DahODIh8KQ27XI7grNCphDYOjfLtMbm/vFssIvFSb8ykD43V2zg 3/y1PItTv+2b1/er9F6jRfXBdCrC3I2y79fGmMWcs06P6Sc1VX319RAeBErYz1lLIRRWI GUAEIHSvSY/HOaYcYu3rdhWxp7/7Ne0Fn5gK7kXj+A21tSL8+wtJEoWsuY6OFfp9PEQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; arc=none smtp.remote-ip=95.215.58.173 Received: from mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52490606A840 for ; Mon, 2 Nov 2026 12:19:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 52490606A840 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev X-Envelope-To: linux-cxl@vger.kernel.org DKIM-Signature: a=rsa-sha256; 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-cxl@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-cxl@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