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Mon, 12 Oct 2026 10:21:18 -0700 (PDT) Message-ID: <3ab63358-8bbe-4457-b21c-bb81bca804cc@gmail.com> Date: Mon, 12 Oct 2026 19:21:17 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm: fix missing page-table destructor in pagetable_free() To: Muchun Song , Andrew Morton Cc: Muchun Song , David Hildenbrand , Oscar Salvador , Dave Hansen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Catalin Marinas , Will Deacon , Mark Rutland , Kevin Brodsky , Alexander Gordeev , Alistair Popple , linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261010112457.49485-1-songmuchun@bytedance.com> <20261010112457.49485-2-songmuchun@bytedance.com> <145CD5DC-6457-4E1E-8B9D-AE7D1EDB0AB8@linux.dev> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <145CD5DC-6457-4E1E-8B9D-AE7D1EDB0AB8@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/12/26 2:55 PM, Muchun Song wrote: > > >> On Oct 12, 2026, at 19:15, Jose A. Perez de Azpillaga wrote: >> >> On Sat, Oct 10, 2026 at 07:24:54PM +0800, Muchun Song wrote: >>> Since commit 49f599666420 ("mm: call ctor/dtor for kernel PTEs"), >>> pte_alloc_one_kernel() runs the page-table constructor for kernel PTE >>> tables. >>> >>> HVO (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 it through >>> pagetable_free() on x86-64. That releases the page without running the >>> matching destructor and leaves NR_PAGETABLE elevated. >>> >>> Make pagetable_free() detect constructor-backed pages and run the >>> destructor before releasing their memory to fix the problem. >>> >>> Fixes: 49f599666420 ("mm: call ctor/dtor for kernel PTEs") >>> Cc: stable@vger.kernel.org >> >> is the x86 case covered for 6.16-6.18? as far as I can see, x86 >> free_pagetable() only uses pagetable_free() since bf9e4e30f353 >> ("x86/mm: use pagetable_free()") in v6.19, so the backport wouldn't >> change anything there. or am I missing something? > > Yes, you are absolutely right — thanks for catching this. > > I double-checked and indeed x86's free_pagetable() only starts using > pagetable_free() since bf9e4e30f353 ("x86/mm: use pagetable_free()"), > which landed in v6.19. So for 6.16-6.18 the prerequisite is not present > and the backport would be a no-op there. > > The correct trailer is: > > Cc: # 6.16-6.18: bf9e4e30f353: x86/mm: use pagetable_free() also, bf9e4e30f353 alone leaks PMD-sized vmemmap pages on those trees, it needs 39406c05f8f1 ("x86/mm: Fix freeing of PMD-sized vmemmap pages") as well :) Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a