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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488c5dc5fefsm24994505e9.7.2026.04.08.05.49.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2026 05:49:30 -0700 (PDT) Date: Wed, 8 Apr 2026 13:49:23 +0100 From: David Laight To: Anshuman Khandual Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , David Hildenbrand , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf/events: Replace READ_ONCE() with standard pgtable accessors Message-ID: <20260408134923.3a44a703@pumpkin> In-Reply-To: <1267a6c0-f8e7-4708-96da-4d131b5c6069@arm.com> References: <20260227062744.2215491-1-anshuman.khandual@arm.com> <1267a6c0-f8e7-4708-96da-4d131b5c6069@arm.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 7 Apr 2026 08:58:46 +0530 Anshuman Khandual wrote: > On 27/02/26 11:57 AM, Anshuman Khandual wrote: > > Replace raw READ_ONCE() dereferences of pgtable entries with corresponding > > standard page table accessors pxdp_get() in perf_get_pgtable_size(). These > > accessors default to READ_ONCE() on platforms that don't override them. So > > there is no functional change on such platforms. > > > > However arm64 platform is being extended to support 128 bit page tables via > > a new architecture feature i.e FEAT_D128 in which case READ_ONCE() will not > > provide required single copy atomic access for 128 bit page table entries. > > Although pxdp_get() accessors can later be overridden on arm64 platform to > > extend required single copy atomicity support on 128 bit entries. > Did you consider enhancing READ_ONCE() to support 128bit accesses on arm64? David