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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 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) X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A5F12120004 X-Stat-Signature: ndp8mg35nczd7tpwhzi6itoiw55ged4c X-HE-Tag: 1791603884-69462 X-HE-Meta: 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 V8naE5/3 magOYq5azXKeS1/pscutww/2JMO9QpHqRUSwrCLRZbP5qU8zWOQ6a2151z6X4I3kztvGeC933jxv7O3Bu/qf7wOteOdzZqq5luLaeiWgz/TFc0lBeHgbO5VY2IWz0UhCoelu2C/9lMl9nAf/0rODbNMnS+9iIQb91exbHRZHlYuQ2Q+YerpCUdBNyCNq0JiUBsT8K8Tlcy9sLqoMnIBuv75tW4cMsd4h0rmmJBryoozFfoIP88n/v6sfR09wSAsMQJyGSTnGXfflascD42/AKsarekQ5xmNEjCeMYhaSVTgFPXHMJMhqtuuKSi8W+fZYMTsnO Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > 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