From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-48.mta1.migadu.com [95.215.58.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8534298CC4 for ; Sat, 10 Oct 2026 03:44:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.48 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791603887; cv=none; b=BG4mgtI9VnAnEw6FFC8mkhV1M0cM9j+pjPnxv3j3um4hC9vZkfIiXEFfIb4aPEvBb8TFGRsXeMZxvBpU6ITeIJjc8kdlw9Sr4prg0/0jaUrFnPaEBe/ca6gVMy48pi/byrP+VLldNjLOMTb2qFRPks72E16BEXIP58nmUDxtG8g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791603887; c=relaxed/simple; bh=0fo0QMf0rjH7MV2/iuitzfDF1YtJ7sax/S4uxQhGa9o=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=Ui8ytS8XFCw8Y0z8cPFPtAxH79K7WGNrtlvuWgwr1106QnGwAgI2RiJaWgy0VyPtul4zXBXyHJzrQSmnYS/YcnChG+gTjSEwWEoLcgENf6rGGp1U0wCrokTH+OsFr0JMn1tgaTdovBRuGDb3ZUnM11qDiRfnQCnzGnXXoc0o10w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ZLC1yd49; arc=none smtp.client-ip=95.215.58.48 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ZLC1yd49" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=0fo0QMf0rjH7MV2/iuitzfDF1YtJ7sax/S4uxQhGa9o=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791603883; v=1; x=1792208683; b=ZLC1yd49raPT2YE6fJK39fORSvmhoQ+qRo6TIfUNdICyeTRbOIPSyf7weuspuE38vRpSN4gb p6+0ej03LOD1jJNcm2KNzO7FGkozS57yvKefcmGG1STBSvbFYc8ZxVErWpNN3aCs/mFJRy4WJMv XBuUAQiDHwREqPS/v3U3almI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 468dd143d2755872; Sat, 10 Oct 2026 03:44:43 +0000 X-Mizu-Trace-ID: 468dd143d2755872 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.12\)) Subject: Re: [PATCH 1/4] x86/mm: fix missing pgtable destructor for vmemmap tables From: Muchun Song In-Reply-To: <1a0f51d9-7931-45a3-ab36-e0642c199a37@kernel.org> Date: Sat, 10 Oct 2026 11:44:26 +0800 Cc: Muchun Song , akpm@linux-foundation.org, linux-mm@kvack.org, stable@vger.kernel.org, osalvador@suse.de, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, linux-riscv@lists.infradead.org, agordeev@linux.ibm.com, kevin.brodsky@arm.com, bjorn@rivosinc.com, apopple@nvidia.com, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <062E1067-B11D-4BF7-A2BA-C71B599A805C@linux.dev> References: <20261008073021.2512665-1-songmuchun@bytedance.com> <20261008073021.2512665-2-songmuchun@bytedance.com> <1a0f51d9-7931-45a3-ab36-e0642c199a37@kernel.org> To: "David Hildenbrand (Arm)" X-Mailer: Apple Mail (2.3901.100.1.1.12) > On Oct 10, 2026, at 04:29, David Hildenbrand (Arm) = wrote: >=20 > On 10/8/26 10:32, Muchun Song wrote: >>=20 >>=20 >>> On Oct 8, 2026, at 09:30, Muchun Song = wrote: >>>=20 >>> Since commit 49f599666420 ("mm: call ctor/dtor for kernel PTEs"), >>> pte_alloc_one_kernel() runs the page-table constructor for kernel = PTE >>> tables. >>>=20 >>> HugeTLB vmemmap optimization uses pte_alloc_one_kernel() when = splitting >>> a PMD. Restoring the vmemmap backing pages does not collapse the PTE >>> table, so a later memory hot-remove eventually frees that table = through >>> free_pagetable(). That path currently calls pagetable_free() = directly >>> without decrementing NR_PAGETABLE. >>>=20 >>> Use PageTable() to identify constructor-backed tables and run the >>> matching destructor before freeing them. Keep reserved and >>> constructor-free tables on their existing paths. This also prepares >>> vmemmap teardown for generic runtime allocations through the normal >>> pgalloc helpers. >>>=20 >>> Fixes: 49f599666420 ("mm: call ctor/dtor for kernel PTEs") >>> Cc: stable@vger.kernel.org >>> Assisted-by: LLM >>> Signed-off-by: Muchun Song >>> --- >>> arch/x86/mm/init_64.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>>=20 >>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c >>> index 70e682180291..a3ea627157ab 100644 >>> --- a/arch/x86/mm/init_64.c >>> +++ b/arch/x86/mm/init_64.c >>> @@ -1003,6 +1003,8 @@ static void __meminit free_pagetable(struct = page *page) >>> { >>> if (PageReserved(page)) >>> free_reserved_page(page); >>> + else if (PageTable(page)) >>> + pagetable_dtor_free(page_ptdesc(page)); >>=20 >> Sashiko mentioned that kernel page table pages and vmemmap pages are >> freed to the buddy allocator before their parent entries are cleared >> and before the TLB is flushed, creating a dangling pointer window. >>=20 >> That's a a real but pre-existing issue, I will not fix that in this >> series. >=20 > Memory is getting removed, concurrent access to directmap+vmemmap is = not > expected unless BUG I think. That should make this less critical I = think ... > (except speculation? not sure if that applies) Agree. So, I will ignore this. Thanks, Muchun >=20 > --=20 > Cheers, >=20 > David