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b=mBZ0FtjM0YSYlsflAtX0hKoQa1FUHh2NQBNtCjhqhMP2UCoyljHoGbkarKREmDZ/a xj7qQiC3jPcX24abrgzSDOdHGkbUvA7YRzJOD9gmW0YjtB3zJX4N4Fj2bIs6xeceeG q0l5f4ppgxbamtpvGTreTicD+MiXlj2FZUgCVwV4dIYC/++v7qO5cTfqR4k8Lkrws3 AJhOPyjBhEP8j84OFrb3QItKGPFOhn2dv80xbwDLNuIoLe/78NfE9xVJveJChIkw3Q I4Rx03gPxCE67XC/EZTenFhnGmVil99p0Zs72XzxroY4uNQ7nCYKtX7j2InoHPeAIK qKH9zaFyJzKIA== Message-ID: <6ca116f4-b9e2-4ad3-a232-bc441f88bc82@kernel.org> Date: Sat, 23 May 2026 00:07:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs To: Tejun Heo , David Vernet , Andrea Righi , Changwoo Min , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi Cc: Peter Zijlstra , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andrew Morton , Mike Rapoport , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260522172219.1423324-1-tj@kernel.org> <20260522172219.1423324-2-tj@kernel.org> 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: 4twno5s3rjg8thsx9sjqhb5xz4gbzrai X-Rspamd-Queue-Id: 4886D180004 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1779487634-196097 X-HE-Meta: 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 F0oRGYA2 J49ee7iHj7kdlwPNLNz1I1tpfT/pddBPk/gsl6v6e6kNqGG7yXeZYfFN2kgO5o99yRKQNr9zPb4tV/dx8y7zXo0ajQWoVxxycDH1HbOjOqqIU9iTta4U3G6LW/4uEnjWeQUHTjb7jdZiZqRPyjWO0OUQsaQ8vNd0+QrudEk9q7U9sxUYO8KPmS4cBcJRYSTUzmsZfICroNO6o5tDzduqDVdSGjNzpu/ZkcYoxwnfKZqytdGex2uDE4MnmYBePA3b8e8/HGrNIc26pni+wdvaRIe91gWQz6BUq0aq1JMLE1zlEDf4HV4orZ5Tr32h1nWDjqiTgiA9s08msWUM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > > +#ifndef ptep_try_set > +/** > + * ptep_try_set - atomically set an empty kernel PTE > + * @ptep: page table entry > + * @new_pte: value to install > + * > + * Atomically set *@ptep to @new_pte iff *@ptep is pte_none(). Return true on > + * success, false if the slot was already populated or the arch has no > + * implementation. > + * > + * For special kernel page tables only - never user page tables. The caller must > + * prevent concurrent teardown of @ptep and must accept that other writers may > + * race. Concurrent clearers must use ptep_get_and_clear() so racing accesses > + * agree on the outcome. > + * > + * Architectures opt in by providing a cmpxchg-based override and defining > + * ptep_try_set as an identity macro. The generic stub returns false, which is > + * correct for callers that fall through to oops on failure. > + */ > +static inline bool ptep_try_set(pte_t *ptep, pte_t new_pte) There are only a handful of valid use cases for this (and the "fall through to oops on failure") makes this very clear. So I'm fine with this, assuming there won't really be a lot of other users besides ebpf. Acked-by: David Hildenbrand (arm) -- Cheers, David