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b=aYDwSm0383Gdgkg6dRBN6iou+Hh0+xVWh+A7/C9B1O+WfdGdJs/gZ2xxZ2mZFqQrG 3GRC3iiE++STQf19+vmj//iQnB2GlGhRi+lVqeC7AsCA7kZ5cjkmM82H19CBDRqJ+v NFX5jO1S62yAnh9albUSwgXsIezzCbzQIDdSGMJtQXUmHurn3+mujGe+NHrCLD+Swf f03DFhawbt9ZfNXpmeI6X2iKBw6TxVY9Ggfv6WMi8WdlGrAx8slDoWior29fxjbHb8 I+CsDpirW6/7E/qUt620Y41Lb7Mpty/4i37thGO6YCOHJBUCkpuu4DRe8JCUN9cDbb wbRQXOn7xHBSw== Date: Sun, 14 Jun 2026 10:29:47 -1000 From: Tejun Heo To: 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 , David Hildenbrand , 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 Subject: Re: [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs Message-ID: References: <20260522172219.1423324-1-tj@kernel.org> <20260522172219.1423324-2-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: rw7h85gpwpcri8zrfs9sequ973sshdq4 X-Rspamd-Queue-Id: 22467180006 X-HE-Tag: 1781468989-392109 X-HE-Meta: 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 WxHqRZpI BQaeS2xR12UI+5cwYpk0vm25BqsB22ZpCuwIHf186DQvgzKOpWYfq0x5GluKTFoMEkh7H6r+mwiATfU+JSMHmUIaET0tJEgn8vIywn8dewYttKTyHcWGfdk//DsXgsyGRKFDQFo8gfV5D43UW5E1FZ/usPWeJ9VvPRA9gcaZLKk+EYqSu4mfsQKLKZns3ZMoMPNxMJw0PV/LtNeu+rGUBZDQZa1BkWgZauVIZ15ORD9H4Ow70/WEo+2iEqbmGv3UgXlHmJ7UUUDzDqUc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Thanks. -- tejun