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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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