From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793306467; b=dV7NW+kizwRFmmCKtxIl63gLFd9pOOTtmqgqDy3zDZXGserVsLXW3ge1te8B9d+JmYRe ANhE3m8Qh0Y+l20UlEknCzSazY1Ot2F4de4yUVPiv0abCpiPOI4+t7QLqKX9/4e9bMq0K 8bk501tNaXw6gkwZRmnDRJfbJ+w/9fXLhnCAuEx0UqWsAkUa/7adB0VFgAFxKNMlT/Z+x f5QEsznVFzycMUlQkrX3SB36Yz+kty1VDT0RNR3oufBCfcMpnTDJyB/n941kYqpgu2NEc tAo6jNrVXCBvaKlrcI+PxcvsRAfQo45pN//6jPBNYYpSYHYjabHBPdU62snRRdWs8oQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306467; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=zTwOe2rhygBTqbimADjsD30DCMGB2E0StBtyrsEknSA=; b=i4dWuDKKcMXQBg42XfirmOns40Dl2AJ+/v8MQvR9F6EyRtIoBLqD/rMaQeYM8fjxvz2T r48bqWZAIgSXdpAnXGSy2FEajcHgXh9VF5WCAh/iSJ0UTKnK1U86oapWL+VHfCbPafVQB H2J6+bIKX3hLk5SOGN5lUs81gyZcqwhzMS/aiPalTq8JTrPEWDK0GxGmBjgBlLmzrPJHZ PYtG3Gd9fNiPy401pZRW/TJdZnzT3hwBlUp2KbSBFq7pB3YOgFDm0bNHPSb3D/qsn+Wne NL8U6JuynPnddVxY8kmRG/jbylxDO8/LRW7nn5hQcl1d2kXQlxuYcwZCVLMlqiDP8ew== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TE1y0ZbL; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56565606A320; Thu, 29 Oct 2026 20:41:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TE1y0ZbL Received: by smtp.kernel.org (Postfix) with ESMTPSA id 265891F01816; Thu, 29 Oct 2026 20:40:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306467; bh=zTwOe2rhygBTqbimADjsD30DCMGB2E0StBtyrsEknSA=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=TE1y0ZbL3VVf4eb0u189422pKiAjJR66N2I9oRbQQKW9568wfoomQtdaN6haewvQ/ QvLKMTWJGEIpLmu872vicnNj8EMylIE6cimSkE7cVVxhve4jg0GGIRmlhdB4EW+Rfs bx4v2727E0rc3ijNbosG45F77CfN2c9fJw31CpRuioX3BtcKRyuofi5KCM412z8Yis b+xHStb8Zv+yfOsQ8t+1K8J/VWSvKbzlyPs3a1VrzphHv9cZ7fI88mgneYvJjxzOHJ v8ViB9WkGVew7svI82MfmrAzh9Hrk1i0lS0t6SRranladPVqdFUN08fQx4ZQ8MBeuv AEoxd+/ch8j5g== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:26 +0100 Subject: [PATCH v2 31/47] mm/mremap: recheck PUDs under the page table lock 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: 7bit Message-Id: <20261029-fixes_core-v2-31-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> To: 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 , Pedro Falcato , 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 Cc: 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, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2380; i=david@kernel.org; h=from:subject:message-id; bh=+B9w/NrDyjyp/nHRZsfFIxa7vmKtKobl06e6HnkArmM=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer+24/V3GfMO74vTaKbNNWy5eXLrUfJ6mT+ijWK8PH W4s/RsTO0pZGMQ4GGTFFFmCgu8bvHy5rrbajY8ZZg4rE8gQBi5OAZiIXx3D/zzBwL2X6+arx9qJ nJHpi56T+PWSp2qJUN7ShvrtW9ett2H4HzPRY6fWRadVIoXiKeVO3i4zbr8QeZnw4P6WpzOSJZS leQA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A 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 Signed-off-by: David Hildenbrand (Arm) --- mm/mremap.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 16e736c72d9c..91f0865f6aee 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -461,14 +461,18 @@ static bool move_normal_pud(struct pagetable_move_control *pmc, if (new_ptl != old_ptl) spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); - /* Clear the pud */ pud = *old_pud; + if (unlikely(pud_none(pud))) + goto out_unlock; + + /* Clear the pud */ pud_clear(old_pud); VM_BUG_ON(!pud_none(*new_pud)); pud_populate(mm, new_pud, pud_pgtable(pud)); flush_tlb_range(vma, pmc->old_addr, pmc->old_addr + PUD_SIZE); +out_unlock: if (new_ptl != old_ptl) spin_unlock(new_ptl); spin_unlock(old_ptl); @@ -503,7 +507,9 @@ static bool move_huge_pud(struct pagetable_move_control *pmc, * We don't have to worry about the ordering of src and dst * ptlocks because exclusive mmap_lock prevents deadlock. */ - old_ptl = pud_lock(mm, old_pud); + old_ptl = __pud_trans_huge_lock(old_pud, vma); + if (unlikely(!old_ptl)) + return false; new_ptl = pud_lockptr(mm, new_pud); if (new_ptl != old_ptl) spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); -- 2.43.0