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Fri, 18 Sep 2026 03:19:15 +0000 X-Mizu-Trace-ID: a4960d5e0aaf2f40 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: akpm@linux-foundation.org Cc: lance.yang@linux.dev, david@kernel.org, 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 Subject: Re: [PATCH v2 1/1] mm/huge_memory: simplify pgtable deposit detection Date: Fri, 18 Sep 2026 11:19:05 +0800 Message-ID: <20260918031905.92493-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260917161359.9ba88d2bcab42db8111130e1@linux-foundation.org> References: <20260917161359.9ba88d2bcab42db8111130e1@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8F7D5C0005 X-Rspam-User: X-Stat-Signature: 6fdqnj181z8qc6ru7dnqen6gjikbbmha X-HE-Tag: 1789701558-83899 X-HE-Meta: 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 ssF8bg+9 VSBHvzmMvpSgUAvFhr7HSW2JzBplnjIfIEpfFhRB9MK6sq6nwXJXDOXu9Rjxr4HXoGk7vmSnAtT4FcE9tpPYCjPFK1GQk5Praryv0MH0d3J9tOZhHECwp8eIPu49T1xBdpyI/rUem7nNb6n3dA3bbN1kmcjSNNOyKSwdkoEUcupliK+ncJEC7eoY/zhfYmBwyY7Kqh5XjY3wc96UJqz/w9y9hqJOaPTGn8OXtkVeUKidwloVfzmHn0XNTh/hUzUYYxauyxyaz3DxzIxXbgg+4feHsQ5T+lI22j1pR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. >Help me out here? > >Also, thanks ;) Thanks!