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b=AEw+KAKoyMIt5WUA0I+U+zx52uQMZaoXINZiiPEWIquiun/uiYDSxVYTwE8oULF/u RhaJMoo6G0XQIXH++yQU6ZUaytHDOXbs07S4afKqRIABqnm7jAoGEVN+OeumGXE5Fs sh59nAMWLtM0dev1x0cbgC9awXS1Uz4xmDd5APFVu1yW5BjCbPPTsALxPGsZGawoTj rfvZsbbclcfK/jrR+gny+hNhEigtUTXuasQPhBYwUk7AS1KPBnqBTLvGiDhTrX0MCE ug5zZCRvRm/U4h/2MmIGoJwbNAQCYe3CI2kEzMZQwWv1shxYJzRLSk1x5jhCLEmNwV AcLD45iSyVhJQ== Message-ID: Date: Mon, 15 Jun 2026 13:49:18 +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 , Will Deacon Cc: David Vernet , Andrea Righi , Changwoo Min , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi , Peter Zijlstra , Catalin Marinas , 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-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D9AA8160004 X-Stat-Signature: 5yei3c1rhd4zmk76zj7ta8keo5ey1imo X-HE-Tag: 1781524165-227672 X-HE-Meta: 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 eI0OxjB9 i1Jbnl2unKksfDr2+2dgEOtVQogtytk05YGjdJ5uDOLHjJTF2YX6ojvS7wnHdDAi0S1NmSBSkf4BZGNMx9wYkFbIBL0cZOMvaKV+4JtQlCjCOicIDP+guHaXNUB1tOZJNsQpSflt0o8LAx1iTFbEbUFd2kcBSk32aVudem2u7IhUzKRqRr9SmWc6iPUKfiTR1EQOI3FRS/ASYULu6p4lzprh/EnVEwObLTsIS2OB1uyk4YDTjsqqkj0WobXb/ORXkHEjnHg6yIcu2xB+EFORCuGe2Zxq9zoe9olJXHKJ/gsLk2vDlwze4SFcMpg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/14/26 22:29, Tejun Heo wrote: > Hello, > > On Sun, Jun 14, 2026 at 10:28:02AM +0100, Will Deacon wrote: >>> +/* >>> + * Note: strictly-zero compare is narrower than pte_none(), but the gap is >>> + * harmless: a fresh kernel PTE has no software bits set. >>> + */ >> >> This comment really confused me :/ >> >> What is a "fresh" kernel PTE and why do you specifically call out "software >> bits" if the CAS requires all 64 bits to be 0? Why is that narrower than >> pte_none() given that pte_none() for arm64 is: >> >> #define pte_none(pte) (!pte_val(pte)) > > Yeah, that's complete non-sense for arm. The comment is about x86's > pte_none() excluding DIRTY and ACCESSED due to an erratum when testing none > and how that doesn't matter here. This shouldn't have been copied to arm. > I'll send a patch to remove that. Is BPF maybe picking up patches from other subsystems up too early without waiting for acks? -- Cheers, David