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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) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B68FD40009 X-Stat-Signature: pemhhkiohuruato31dma3rpqn4z7t5sk X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1775652572-645008 X-HE-Meta: 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 ZaY9qljZ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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