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Mon, 12 Oct 2026 13:29:55 +0000 X-Mizu-Trace-ID: d7c9edd7e757cc90 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 v2 1/4] mm: fix missing page-table destructor in pagetable_free() From: Muchun Song In-Reply-To: <919fcaa9-5ebe-4940-b4fc-59ea0c655ec3@kernel.org> Date: Mon, 12 Oct 2026 21:29:35 +0800 Cc: Muchun Song , Andrew Morton , 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 Content-Transfer-Encoding: quoted-printable Message-Id: <77D942CF-B657-4735-9B95-1C6B38DD0F46@linux.dev> References: <20261010112457.49485-1-songmuchun@bytedance.com> <20261010112457.49485-2-songmuchun@bytedance.com> <919fcaa9-5ebe-4940-b4fc-59ea0c655ec3@kernel.org> To: "David Hildenbrand (Arm)" X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 190A140009 X-Stat-Signature: 8k73tzk7o13y4arjp3sw8s53h6i9d8st X-HE-Tag: 1791811796-633944 X-HE-Meta: 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 ottEbPHe sKD0pYJr+C4AjBidMFhwuUYrD+TauvTCzdsQP3NPF7RDWsJTD1Uq51mccg1ar7V4NxX2czI7edrHNFFrrChJgbxm07eB858MW68ooVxvzuhFm+wRhD/SZrbo8Tco3KImsEDEJ68skCi5hzfOwS6h3EQjjs2RKwWBrwaKfB+VT7Q0Juh409aBbPVbJu7QSxUTZc+xRACxZ4dRfwv6xoNklzWnO0EXeFA9mJL2AT043evb/0Vffai5wPjA7cZqTUES90SrQwxjAgUc19swOjtGtMNrnyYKhgCUGouOfZURVz9Y00c0nwl3pDGKOEma3J3js4mv3f54BwK68zvvIbJAx+CibhqIidv7Rhn9kRlP1pFEA8S0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Oct 12, 2026, at 21:27, David Hildenbrand (Arm) = wrote: >=20 > On 10/10/26 13:24, 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. >>=20 >> 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. >>=20 >> Make pagetable_free() detect constructor-backed pages and run the >> destructor before releasing their memory to fix the problem. >>=20 >> Fixes: 49f599666420 ("mm: call ctor/dtor for kernel PTEs") >> Cc: stable@vger.kernel.org >> Assisted-by: LLM >> Signed-off-by: Muchun Song >> --- >> v2: >> - Move destructor handling from x86 into pagetable_free() (suggested = by >> David Hildenbrand) >> - Trim and update the commit message (requested by Dave Hansen) >> --- >> include/linux/mm.h | 37 ++++++++++++++++++++----------------- >> 1 file changed, 20 insertions(+), 17 deletions(-) >>=20 >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 5cca90fc1df6..771a7d60b0a5 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -3969,23 +3969,6 @@ static inline void = pagetable_free_kernel(struct ptdesc *pt) >> __pagetable_free(pt); >> } >> #endif >> -/** >> - * pagetable_free - Free pagetables >> - * @pt: The page table descriptor >> - * >> - * pagetable_free frees the memory of all page tables described by a = page >> - * table descriptor and the memory for the descriptor itself. >> - */ >> -static inline void pagetable_free(struct ptdesc *pt) >> -{ >> - if (ptdesc_test_kernel(pt)) { >> - ptdesc_clear_kernel(pt); >> - pagetable_free_kernel(pt); >> - } else { >> - __pagetable_free(pt); >> - } >> -} >> - >> #if defined(CONFIG_SPLIT_PTE_PTLOCKS) >> #if ALLOC_SPLIT_PTLOCKS >> void __init ptlock_cache_init(void); >> @@ -4078,6 +4061,26 @@ static inline void pagetable_dtor(struct = ptdesc *ptdesc) >> lruvec_stat_sub_folio(folio, NR_PAGETABLE); >> } >>=20 >> +/** >> + * pagetable_free - Free pagetables >> + * @pt: The page table descriptor >> + * >> + * pagetable_free frees the memory of all page tables described by a = page >> + * table descriptor and the memory for the descriptor itself. >> + */ >> +static inline void pagetable_free(struct ptdesc *pt) >> +{ >> + if (PageTable(ptdesc_page(pt))) >> + pagetable_dtor(pt); >=20 >=20 > We do have >=20 > static inline void pagetable_dtor_free(struct ptdesc *ptdesc) > { > pagetable_dtor(ptdesc); > pagetable_free(ptdesc); > } >=20 > ... can we now get rid of pagetable_dtor_free() and simply use = pagetable_free() ? > (separate cleanup) You're right, that's exactly my plan. >=20 >> + >> + if (ptdesc_test_kernel(pt)) { >> + ptdesc_clear_kernel(pt); >> + pagetable_free_kernel(pt); >> + } else { >> + __pagetable_free(pt); >> + } >=20 >=20 > This goes into the right direction. I'm still confused, but the less = freeing > functions we have the better. >=20 > Acked-by: David Hildenbrand (Arm) Thanks David. >=20 > --=20 > Cheers, >=20 > David