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b=JDpOapUC4lyxBS7OBzBbsX9la9jZguLY/7ZDWpQtqhskKwpWnVzhzdoiJGu8eL1ta QA3C8nrU0b3TsjiwKgTRsd08MPw8MxrMkmv+y9KmWqMEhKBXsTg3q0gjKJUTOBvZ8C rCM9nR/xfFdSAiMwGVWSv4bEiZtlBB1TUOqrtlO/r/1tzyF6dGpIYC91xK/soePw0d umZ2SvIKxdiozcutJrZpumH+VoipWMw8+oDMUBOvm5hEyAb+NAWcJtgODx0n2+Sthy CMero+r74dQcFLS0Q5KowSCFVVQGW3/t5RAhIRgNXJN+zvmISjxX0RaliIBx7hefCH 0m1uc6nZv4BVw== Message-ID: Date: Fri, 18 Sep 2026 13:09:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] mm/huge_memory: simplify pgtable deposit detection To: Lance Yang , akpm@linux-foundation.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260917161359.9ba88d2bcab42db8111130e1@linux-foundation.org> <20260918031905.92493-1-lance.yang@linux.dev> 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-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8CEC114000B X-Stat-Signature: 3c44u81ebp43bmzcjsh6au5gp36qpzkm X-HE-Tag: 1789733066-782309 X-HE-Meta: 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 TKndK4MU 938pfS6CFZydAuwwrXJOLyJpzXkoDabFliqcjsQnSnmvwmHwTnEhD1KWR9NbWm9kfya8AQAQN6PpkE39DhhWvajhFKIge8lwmJ+mnmChLK3pDRRFaEDYfXugBzpN26MyRIvVs5nYwg6W+IvremfImcTqq8T40NVTBdjq/V09VRsiB8U5q3JKsN9i/pQtViQP/Kb2091bwFohk12KlOKRBJwxXtPI1bmz4kYelFeAhJlz4mlP73/xXWy2ip2qp3G2LYOhZ9B8Vs565alJGHfemHdbT4a3D5h9ZlX4C70w30zw5IlZ9Kf7CMsPzEg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/18/26 05:19, Lance Yang wrote: > > On Thu, Sep 17, 2026 at 04:13:59PM -0700, Andrew Morton wrote: >> On Thu, 17 Sep 2026 13:40:15 +0800 Lance Yang wrote: >> >>> Whether a PMD has a deposited PTE page table only depends on whether the >>> architecture requires deposits or the VMA is anonymous. >>> >>> Implement this rule directly in vma_has_deposited_pgtable(), avoiding >>> mistaking a non-anonymous raw PFN PMD for one with a deposit and attempting >>> to withdraw a page table that was never deposited. >> >> A large part of my life is asking $LLM "what are the userspace-visible >> runtime effects of this bug". Because NOBODY EVER TELLS ME!!! > > That's on me ... I trimmed too much from v1. > >> This time it says "Processes using PMD-sized raw PFN mappings can >> trigger a kernel NULL-pointer dereference when the mapping is torn >> down", which sounds kinda important if true. > > There is no known in-tree workload that triggers it, though. Mostly a > defensive/simplifying change. Yeah, it's not a fix. -- Cheers, David