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Fri, 1 Aug 2025 00:15:16 +0000 Message-ID: <96a36e37-5558-4c91-9591-8e5a77dce850@intel.com> Date: Thu, 31 Jul 2025 17:15:14 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives Content-Language: en-US To: David Laight , "H. Peter Anvin" , Dave Hansen CC: "Kirill A. Shutemov" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , "Peter Zijlstra" , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin , Jonathan Corbet , "Ingo Molnar" , Pawan Gupta , Daniel Sneddon , Kai Huang , Sandipan Das , Breno Leitao , Rick Edgecombe , "Alexei Starovoitov" , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , "Andrew Morton" , Luis Chamberlain , Yuntao Wang , Rasmus Villemoes , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , Geert Uytterhoeven , Namhyung Kim , "Arnaldo Carvalho de Melo" , , , , References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> <20250728201137.113d0f45@pumpkin> <98BE7799-DA6C-4267-9E03-E6F68263D250@zytor.com> <20250728203809.7bebf01c@pumpkin> From: Sohil Mehta In-Reply-To: <20250728203809.7bebf01c@pumpkin> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR02CA0016.namprd02.prod.outlook.com (2603:10b6:a02:ee::29) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR11MB3320:EE_|SJ5PPF0FD67B0BC:EE_ X-MS-Office365-Filtering-Correlation-Id: 9dba244c-e98d-45dd-50f6-08ddd0907dee X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024; 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It's rep movsb without any of the performance. > > And without the massive setup overhead that dominates short copies. > Given the rest of the code I'm sure a byte copy loop won't make > any difference to the overall performance. > Wouldn't it be better to introduce a generic mechanism than something customized for this scenario? PeterZ had suggested that inline memcpy could have more usages: https://lore.kernel.org/lkml/20241029113611.GS14555@noisy.programming.kicks-ass.net/ Is there a concern that the inline versions might get optimized into standard memcpy/memset calls by GCC? Wouldn't the volatile keyword prevent that? static __always_inline void *__inline_memcpy(void *to, const void *from, size_t len) { void *ret = to; asm volatile("rep movsb" : "+D" (to), "+S" (from), "+c" (len) : : "memory"); return ret; } static __always_inline void *__inline_memset(void *s, int v, size_t n) { void *ret = s; asm volatile("rep stosb" : "+D" (s), "+c" (n) : "a" ((uint8_t)v) : "memory"); return ret; }