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[114.38.149.183]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2e97e5d4e51sm29796255ad.1.2026.10.18.11.29.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 18 Oct 2026 11:29:06 -0700 (PDT) From: Yuan-Hao Hsu To: Rik van Riel Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, Andrew Morton , David Hildenbrand , Jason Gunthorpe , John Hubbard , Peter Xu , Suren Baghdasaryan , linux-mm@kvack.org Subject: Re: [RFC PATCH v3 4/8] mm/gup: break out follow_one_pte() helper Date: Mon, 19 Oct 2026 02:29:00 +0800 Message-ID: <20261018182900.671-1-aa9736195201@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <7ba9d2e6370d6134ad34cdffcff5cc79b9192df1.camel@surriel.com> References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-5-riel@surriel.com> <7ba9d2e6370d6134ad34cdffcff5cc79b9192df1.camel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1D7EC40002 X-Stat-Signature: 7p6efjtrhy6dxc4sg677y3x15jiwckxs X-Rspam-User: X-HE-Tag: 1792348150-984059 X-HE-Meta: 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 JmzBysS6 D0q4Yl0EiyjON/ikeTItOXCelsFsRdobON0mMmhWgUmdSM+Ue8sigTtypBWwG0Qn0hP4/LjzvMltCJEdbUKHTC4jerT87Q04o9EyfWeitp04k43oY0ItMIbyooEP+5iPqT0eszQUEkMmAKIQDnVi2Chtk+YZ2TfaM3d5NuT+mP/rGuNMGYBBGqAkAAvxndFM2uwJuG3cV/QUZ+ar6i6Gn73VES8Nrc/YAy7fW/qKFLYqiTcW1Ozddre70rNnhhxaax5dcI5k2Rstl73cvztDdNjV7/PEIxM+O/Oo3Hu+0udDnlFcZ9V1zPr5140DLA6xeRbDrHf5pvmGylu4piy3yugtsqex+c719rS720NZMH/bJYd+fASRQnOTs9CIAPu2bPW/SAOPrwGsQ6igDtol0bJpWLH5tCiFFThcBFaABK4ryrtE5ageZbhmaQg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 28 Aug 2026 22:11:07 -0400, Rik van Riel wrote: > On Fri, 2026-08-28 at 16:47 -0700, Suren Baghdasaryan wrote: > > Before refactoring in the above case we would "goto out" and > > no_page_table() would not be called even if pte_none(pte). Now I > > think > > you will call it if pte_none(pte). I'm not sure if this does not > > matter but this seems like a functional change. > > Good catch, now we may end up calling no_page_table() > on a VMA where we are not allowed to write, for a > FOLL_WRITE access, while before we did not. > > That might turn 0 into -EFAULT in some corner cases. That exit is reached with a present PTE: follow_one_pte() has already returned 0 for !pte_present() above it, and pte_none() is false for any present PTE. So "!ret && pte_none(pte)" in follow_page_pte() can only be true on the !pte_present() path, and the old "goto no_page; if (!pte_none(pte)) return 0;" sent exactly that case to no_page_table() as well. The can_follow_write_pte() and pte_protnone() exits still end in a plain return 0, as before. No functional change here, so nothing to fix for v4. Yuan-Hao Hsu