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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453646d1391sm147960395e9.9.2025.06.24.09.50.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Jun 2025 09:50:05 -0700 (PDT) Date: Tue, 24 Jun 2025 17:50:01 +0100 From: David Laight To: Segher Boessenkool Cc: Christophe Leroy , Michael Ellerman , Nicholas Piggin , Naveen N Rao , Madhavan Srinivasan , Alexander Viro , Christian Brauner , Jan Kara , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Darren Hart , Davidlohr Bueso , Andre Almeida , Andrew Morton , Dave Hansen , Linus Torvalds , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/5] powerpc: Implement masked user access Message-ID: <20250624175001.148a768f@pumpkin> In-Reply-To: <20250624131714.GG17294@gate.crashing.org> References: <20250622172043.3fb0e54c@pumpkin> <20250624131714.GG17294@gate.crashing.org> 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-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: AB91140009 X-Stat-Signature: azh351bcttchzntbcqtpdwqqb6sc95w8 X-HE-Tag: 1750783807-861149 X-HE-Meta: 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 pFVvgyWH c4hBlnALQjVtCccbs44vo0aBjixeZ5Fy2L4KXeUi5jt9Ab5kIND8QNUnjtLUO+SToJvYq0hZziqgrarUVMnjHANCkHAxIUbHDokZYc8tJIcXxz+SL66RlSH2L1rLwnMT8pt0DfJexjJq+iFW5ac/iL3z/1RhxAIXFI61T2E+rtZUVQZjW2NoO4+MA6T1CdNXlT5Z0DYvRHAAzkNvZF2vtJqW0NbrVGo3p8KV8RNal97YhUfXFkmwwaSIu9hhZT5HCSfjUoU9BlN9dy2sVvwGxH4Pile0A2qBHhrje99IVNz+N4VtOL5jKqDiVAGRF1hxR0KeIaOyQYYUGFsZbRwT2YHYmxrMY+wqFrhUxQTFf5JZmifzHLhYd2abwj4FSMfyvFeM1fZcfm8Nsbrp1fDiicEDfe2+F+b/09cqJk6/u3mGzNzyOqizJe/gtI9K6Wj/Osh99lFPKbb12TAE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 24 Jun 2025 08:17:14 -0500 Segher Boessenkool wrote: > On Tue, Jun 24, 2025 at 07:27:47AM +0200, Christophe Leroy wrote: > > Ah ok, I overlooked that, I didn't know the cmove instruction, seem > > similar to the isel instruction on powerpc e500. > > cmove does a move (register or memory) when some condition is true. The destination of x86 'cmov' is always a register (only the source can be memory - an is probably always read). It is a also a computational instruction. It may well always do the register write - hard to detect. There is a planned new instruction that would do a conditional write to memory - but not on any cpu yet. > isel (which is base PowerPC, not something "e500" only) is a > computational instruction, it copies one of two registers to a third, > which of the two is decided by any bit in the condition register. Does that mean it could be used for all the ppc cpu variants? > But sure, seen from very far off both isel and cmove can be used to > implement the ternary operator ("?:"), are similar in that way :-) Which is exactly what you want to avoid speculation. David > > > Segher