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=1793440099; b=VSLz6l7JnrKpATtJ/SQVw8c8TESHRDr2j601D6NLZ7jPESwxrzVezlCdmoBwrUa11ex8 fsIg4VJQPsTx5VmAYptKVZQ2YPyUXT8z7Iujtlyq4GltHJnApbZTSdVncC/buS+SFOiYA trAygma9T07RVCCAL6gNrm4VHHlOgPxzcBhS6dy08YcF4t4EiV+R9LCaJKggLslGn+ZzN RDiF3Oj/Lt8K2ugro/N20VkozQLM9VmV5DLe9ow005LWZej4S2y6lqbJkRwmO7M4w1kvL g5s0meHcqV9SxNLszOuZAp3nNDTg7yoRA335iW/E/adbYriB5/7T4NdPb2Ptt1uBXRg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793440099; 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=DxsTnHZLfef+ZwV+bvdRNnaTqozvDnboMuYB5CYD3jE=; b=h+IoMX5sDggLl6VPnfIHPBBgnEPPIgL/3Ec1A1JrgSjtGYlIMbyyGHlN6p0PfmVkKWAL a8YW6kAnV/vlce8AYY2NSXSXFGKyCbHw+IbXQFxx+XZdHQgZDKGY+jW4URZazy7q3NYbq O2wJ90+WxPA2eTCg0jRG2k5utYf0iWB5fB4wXtyiuvawt+c1x0S5EjjTFxbBg6vzkj7gl Kp4PEtZOohvWDegpPHg4un9B1FgzTrM41WVQRkuwBid2esFe6zbCgMxWFhCAqkuPS0DDr vBbYN3aH2MYrVYetk5AiH9jRD1bJ5DQVUgBuBGStAzF+/KtbGxcTx+ysoD6evzkardw== 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=QoEpOhUZ; 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 F3E85606A31E; Sat, 31 Oct 2026 09:48:18 +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=QoEpOhUZ Received: by smtp.kernel.org (Postfix) with ESMTPSA id CADAB1F00A18; Sat, 31 Oct 2026 09:48:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793440098; bh=DxsTnHZLfef+ZwV+bvdRNnaTqozvDnboMuYB5CYD3jE=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=QoEpOhUZRVT5ren8mNvEjqn1fyrCuCi3IqzacLFBc1u2HJO2oZExxcKCe19eR+RGQ 8iwI8BvPZqNo5/jrqNSTGGo88w098M0MYwCIhUk6LpVbPz2i7KC/apSep2/KNgnikI CCZGsUUg6SYpN5WNaqgo8h1JdSLlrj3hYY7CzMCHMtG1ewJfyApyunEHXCarGJoL5Y prMZdGWKplHeXSIkx1fzFbYsB0I7gZ7MmULj4BhOGc7AQjO7OtPdPPIl2SKAWZRQVo g2l/0yxLop/YPFutY9Vnr3DZWe2nReOil0JTX8tcvbh73/vuVLd2Z0v/zRvWBDB3E/ ebhBYFeK5WLLQ== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:40:00 +0100 Subject: [PATCH v3 31/47] mm/mremap: recheck PUDs under the page table lock X-Mailing-List: linux-fsdevel@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: <20261031-fixes_core-v3-31-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@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, Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2437; i=david@kernel.org; h=from:subject:message-id; bh=YLac1XnofZU1UqgkNCzS2hgJEvURcnZijflAh/9PoUE=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebs/M2sG2+2aZx+o8Q2HJ9yX+F78wragxXn+sMS6Ri WfxVTGfjlIWBjEOBlkxRZag4PsGL1+uq61242OGmcPKBDKEgYtTACbyw4vhN4t60MezWt6cQpaK d97fOyKk439i2WG5kKkXGDQZLs+zLWRkWKKb/J/dqOvfq/UKWfytT/oFeqdGrpN5+3lT6H7Tbt3 //AA= 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 Tested-by: Muhammad Usama Anjum 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 16e736c72d9cb..91f0865f6aeea 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