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a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791578591; bh=JxCU4kgy6yuLL3vMKMbNFEILfGTC3AEpOEg/HFNIu60=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SP23AZs/ZMLS1F7HAiY5z7X5nF2RAOysCWRarEHnTfxNiZ6ItX8IcZVYkiT3Xyrzw Ts27Z3REnfSbgPcmeCHEvXQfI5R0zszY/WgI7oNDs5Uuk4RtQelzpmDtOVb/O1mgbC ESJ+fGuVP07bnVnyI4wWN+oqUM/udZKJQpOIxZ7jC0KEakCwnj/veq68QxurhH1xPa x4QNtZRPeZ9Z9OSE+fx43CSrHusaCl/LHAxjU2JLx+s5fnC628xxa9yw0FVkBWzqfI F/V/SeQf2YozHcliqBqzshsNtBivlYnNq0VSVj9gwdZur95pXceUhTxA42KBjet0PE DuKW2pGkIo/aQ== Message-ID: Date: Fri, 9 Oct 2026 22:43:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/4] arm64/mm: fix destructor for unconstructed hotplug page tables To: Muchun Song , akpm@linux-foundation.org Cc: 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, muchun.song@linux.dev References: <20261008073021.2512665-1-songmuchun@bytedance.com> <20261008073021.2512665-5-songmuchun@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: kqikjunx1oq4puhsuncgtpywb4gkkrcy X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 8DA111C0004 X-HE-Tag: 1791578592-734998 X-HE-Meta: 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 0g0x8OSp NvQMHsrPS5UlK5fXL/ELhwjogdo0oiufK8XexW3HuAsyJJerkc48Za8SbIuStT5h+ea/D1+PIrsoX/aIvgQIXv+eHTeyV5yLxNEo3q9ChkC+lnwMqMvlkxSrzf5y8vlfH8C+zC+v7rnIJqk0l6PSbXCUoUpzj4CNQuHVk1Ab4SZ4pJExzv9DUAbI/qijyyaClj86SrxXUba5onduYHC7o+ZMPYc5HyG1CHRJ2/+uo5/E+Cj4TfdBjBnzqLMxVLBg++KbMzqeDOIZ0Wllm4gzg8tLGLh74w+rZoi2nz5UJFFt36nzZZcWnZSmlKg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/8/26 09:30, Muchun Song wrote: > Commit c594b83457cc ("arm64: mm: call pagetable dtor when freeing > hot-removed page tables") made free_hotplug_pgtable_page() > unconditionally run the page-table destructor. This matches page tables > allocated by the arm64 mapping code, which runs the corresponding > constructors. > > However, arm64 also uses the generic sparse-vmemmap population code. > Runtime intermediate page tables allocated by that code do not run a > page-table constructor. Why do we have that inconsistency? It seems to cause pain :) > Freeing one during memory hot-remove therefore > runs a destructor without a matching constructor and corrupts > NR_PAGETABLE accounting. > > Use PageTable() to run the destructor only for page-table pages whose > constructor initialized them. This keeps the arm64-created page-table > lifecycle balanced while safely freeing constructor-free vmemmap tables. > > Fixes: c594b83457cc ("arm64: mm: call pagetable dtor when freeing hot-removed page tables") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Muchun Song > --- > arch/arm64/mm/mmu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 7343ac9294f8..688b33095651 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1495,7 +1495,8 @@ static void free_hotplug_page_range(struct page *page, size_t size, > > static void free_hotplug_pgtable_page(struct page *page) > { > - pagetable_dtor(page_ptdesc(page)); > + if (PageTable(page)) > + pagetable_dtor(page_ptdesc(page)); > free_hotplug_page_range(page, PAGE_SIZE, NULL); That results in a __free_pages() for ones allocated by sparse-vmemmap population code. Are we sure that's the right thing to do? This is all so inconsistent and confusing :( -- Cheers, David