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=1794514104; b=J+iS8L9b+/UYx2AVTS1y1X9omNtpesFS3KgxcBwEK+cRsE5j4apSumCPnxW8+rLz22Gr l8kkOdpeN62zVNXzc9ZmImUcS9UVBXuxcPvJBmbUUheEJ7soLWttGvBc/CcN9j0ziep/P 9icSRBNnb6j/63ZKWRqV7YOdl6VqpdGJphOgnqGfk5/NgsUEDuoDZgQogMKJDU295Glg6 6nJ01on1aoULu8weAMAK1GbaWgn7hRie4WO+aL/Flm49LcaCHWdY9CgcFHPmVFET5E0dk n8l5WG5beZ5RlBsLKieLmUiEo7yMn6GcM2BAfms4pRW3MCM8LrPlF78UxsTHmWNOKmQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794514104; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=k7lyuIb4ox+Rw7/ArCtjyqQ0iIPzZdkPkfVfuImeHFM=; b=pBikgrEXrrE3ii+iXpIll9SzJGlF7/oyBp6IGdDKTl1i8ysO3YNsgBdAc6yrCFWR+zcg 4SawmkpvbnuDpDYQKnQA/HwcG3PNDCRbjNUGwODSWj3oWlsw4gxhQV74a1TbSJ/yCvyaf 7P1VFNeHf67i8yEbf7/0gn9QGZ30nl7EShzHnCYZX9J87yXL8ZRhfZci0R3M1/j4x0YO6 d4WpgQj/1vbPiDBZ5VxSA1vk0J6rW5qrPkjq7MPIIj2OBxVbs28ititAF6Lfq98cj6TjF AAAXvwMLkdhbWCP6xXOAOStp4Jm0NgDRwHFwHknm/IWLQIZRl+rslXeh5UyD5ckZM3g== 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=QL3VzyG3; 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 42346606A31C for ; Thu, 12 Nov 2026 20:08:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QL3VzyG3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 424E11F000C4; Thu, 12 Nov 2026 20:08:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794514104; bh=k7lyuIb4ox+Rw7/ArCtjyqQ0iIPzZdkPkfVfuImeHFM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=QL3VzyG3k5E+OAo1cc+wnl8LJwE401yol6CTMyZj1VRLhJz9StnDr2ychN+YQpUyg rkQE+rwVr82jKC3BJtcacHbras0FMiYCKrvGEfDu6YuNyO82nskydfvsmGndUxYnc7 RM97BVTKoBpMzZDqCcWPg2t8PViCqdbJTqupF5hyxgE+1cAS2CmeoiUZ3VEuexGd7X PvkJY//MzjlNySqbRcD+cAYX9t4oq2IQh2RlP/ZRT7ebwy0KeFaRnZMRENMQFJf1Bl Nto9eeCLKgbpdQycg+Xa+3wOSTuDcR25Jf1paVc6ZDCz7RYczoWPzgwtaQQnONTCpJ y4MatVpAs+rvw== From: Sasha Levin To: stable@vger.kernel.org Cc: "David Hildenbrand (Arm)" , "Lorenzo Stoakes (ARM)" , Pedro Falcato , Muhammad Usama Anjum , Lance Yang , Sasha Levin Subject: [PATCH 6.1.y] mm/mremap: recheck PUDs under the page table lock Date: Thu, 12 Nov 2026 15:08:21 -0500 Message-ID: <20261112200619.3454339-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109201833-failed-6.1-402882943dfa@kernel.org> References: <20261109201833-failed-6.1-402882943dfa@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "David Hildenbrand (Arm)" [ Upstream commit 402882943dfa8bab5c2bcc66189f9fb2828f248e ] 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 Link: https://patch.msgid.link/20261031-fixes_core-v3-31-d6437171ecc3@kernel.org Reviewed-by: Lance Yang Signed-off-by: David Hildenbrand (Arm) [ sashal: adjusted context for move helpers using direct vma and old_addr arguments instead of pagetable_move_control ] Signed-off-by: Sasha Levin --- mm/mremap.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index ec66e7be8afea..fd1f9ed45eb93 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -345,14 +345,18 @@ static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr, 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, old_addr, old_addr + PUD_SIZE); +out_unlock: if (new_ptl != old_ptl) spin_unlock(new_ptl); spin_unlock(old_ptl); @@ -387,7 +391,9 @@ static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr, * We don't have to worry about the ordering of src and dst * ptlocks because exclusive mmap_lock prevents deadlock. */ - old_ptl = pud_lock(vma->vm_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); -- 2.53.0