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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 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 X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 692DA12000E X-Stat-Signature: 4yogrrwf4fhzpduhdooz6ywtykhsymgh X-HE-Tag: 1791825681-793377 X-HE-Meta: U2FsdGVkX1/0tIc8yLv6cAfO61IOxgWwmBGxrxOvlHOwKiHYJ8P3b4mL2LCi7PU3piYn/9Rf+WTzr/p6gOvMBjc3fmFtdgPilK8bl+ro23At2ozyomHHWnlFZJ4E/4KiLSCEWrhG7hKKFzKXrbIE9Kv42AcCzqlFjK1Wpcp9qzJXx1B/aHp7uZgeUyEohF3hbtCYTYLuvzvKmMOSqKG9zYdEm3XfoS8+f4R9928wVtTahga1c5Kjjcs3g0GtLmZCIPKAkKwG4EDyhvzpAa5LaKgjwhPT+1aq1BoKAc39xiWA0wNhMbMi40gGu8unuFGjX+sfCpZnUWHqb+aeqbD9XKa+InrtlhkB7/pXk3x0zVWwiiIVaEwjuNM6rRe+uFbDSx6uUgyKcJGUIy6ZWIp2vIpToypqew7482J6VbeZPjfFUXgDG0bZ75ia11fYY8Rf0Wh100BkeFGko7o9lFGFhLdSux52b343SSOpN45sEZsY3T7r45QK9oyenhM+7u4OdaGzMTya9eyU1m38xwmB0sIuNGU8U5zSQIzqSYKkYsEf5AQQeSRA/FL+3byZSh4jeqbQDla7IE+MjtXgvJJXrlKtGxlxb5cB6Ohwk2iFzkWwtclnUbZtHNb9kz8FtcBLs+NLtk3KSFII/yh3BsaXIh74idl7KQVpkPbhEICH3HE9wZxAHI0dez2xIWrybMALl5S1fkSOF/oW525shPfgx500kmXVttTIv08lvOux6x47LRn4bo+8WfDCgZ4w6GoodgFbNQdW9XAJw5ZzkCFuLYe4KMT7A4+A2ClmoN3b9M6q/ya+7H6LjLwMIFjNEohdwXg1Sjkd2Af912NnaGwLK3/34gW3SisprXjL8FEztaJfybTY1Mzf1SSsVxlcQPHzOqRvd+dfcdT+7arMGqo3BjV/14b/xg0fvIezcywLZPHiVCAwPQHYfFvL2TqZDcoPEQQ3xCyfvHRPFyvMn5x EEkqp+JK ow03qJT5ubHvRb8ez8559dN5HpOwB/gUXezMnVHmG1WaUY1+V/GJuRq7te0RvrsTPvUSFydjPXHACWq8j66/wlcRLJ6Ju4lKsYyn3kuiMUf3GHaDvW3A7rIPKsD3CEIKr+Z5UP3mi0XV8x8IQ796gSnzmB0oiUnO2ayxr2fqrz2gIBL+ETVyb+IxZYUdobnYi5/YBk+DmrbTHhnm+34sGf2SS33k3bd28OykrIre5ubQ0qORgWcmsArj9b4bZZx3DfPOQKIU6N2aF26Ra6poN7+LuSog9Tid4vluzK/1CIBLJQyV/RZtouiYhxPQc9He378AU58/9uoWFtjhe7KfLfqRkaJGstcH4HPcMt4YvJnesYgkYmsPTCYjthrCU91cJLcoqaWywaYlPuwxpZE792l4yyYHOAi5Bk9ZS+z0puv36wYTX0Sf/31BN4JWVm5UznQ4qp1Hzmz0sJfQylsvB+cjEF59//j+C6isFbtDQQubPybsV1p/BrZNcMoJtzc5EHdbE6XXWgbuvhwwOh5BsvtHP8YOtwX/cfwIAsBCenq9OV9vMqwRXOjr9yQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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