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Thu, 08 Oct 2026 08:33:13 +0000 X-Mizu-Trace-ID: f276eb58ea604195 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: <20261008073021.2512665-2-songmuchun@bytedance.com> Date: Thu, 8 Oct 2026 10:32:58 +0200 Cc: akpm@linux-foundation.org, linux-mm@kvack.org, stable@vger.kernel.org, david@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: References: <20261008073021.2512665-1-songmuchun@bytedance.com> <20261008073021.2512665-2-songmuchun@bytedance.com> To: Muchun Song X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A7105C0002 X-Rspam-User: X-Stat-Signature: ifaacinmo8p7yqy4q9fiqzy34exs46t5 X-HE-Tag: 1791448396-828563 X-HE-Meta: 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 nVl7DqtA Xt2XGrzNSC61tmqUzm+5p1rMiSO4hnAECAQqWI9H1GztaXhsdRmCYxPe9tE7ci5GLQfKzyefl0xi2VBEkI/cNmtIZEFLP/dmsDFRfVBs5yke5wzdNAeWWHJo3ZpEyx/5LMlgZtDB5EZadGRS0/JdmRjeB0evqeVWk9C3XfMny3DwKdm5RxF95SZAl1W36Nw133Ac0I/Dbj+8t+64ObNauXDEnFp8V0ip9WoY/b0TUVYgtUGF0IWkq4lPJaKO+13jM81FeKFpiu+1kksfAqNEyUA06Ja2VtKe/7cJ4X0hETc7AwanHaNG67jS+Yw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > 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)); 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. That's a a real but pre-existing issue, I will not fix that in this series. > else > pagetable_free(page_ptdesc(page)); > } > --=20 > 2.54.0 >=20