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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b77db8a944sm8455273f8f.52.2025.07.28.12.38.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Jul 2025 12:38:21 -0700 (PDT) Date: Mon, 28 Jul 2025 20:38:09 +0100 From: David Laight To: "H. Peter Anvin" Cc: "Kirill A. Shutemov" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, 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 , Sohil Mehta , 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 , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives Message-ID: <20250728203809.7bebf01c@pumpkin> In-Reply-To: <98BE7799-DA6C-4267-9E03-E6F68263D250@zytor.com> 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> 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-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 96CC116000D X-Stat-Signature: u7wnzs3jt6ypw5ckk7or3xntxa3turbc X-HE-Tag: 1753731503-867481 X-HE-Meta: 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 IplfR+5P 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 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 Mon, 28 Jul 2025 12:28:33 -0700 "H. Peter Anvin" wrote: > On July 28, 2025 12:11:37 PM PDT, David Laight wrote: > >On Mon, 7 Jul 2025 11:03:02 +0300 > >"Kirill A. Shutemov" wrote: > > > >> From: Sohil Mehta > >> > >> For patching, the kernel initializes a temporary mm area in the lower > >> half of the address range. See commit 4fc19708b165 ("x86/alternatives: > >> Initialize temporary mm for patching"). > >> > >> Disable LASS enforcement during patching to avoid triggering a #GP > >> fault. > >> > >> The objtool warns due to a call to a non-allowed function that exists > >> outside of the stac/clac guard, or references to any function with a > >> dynamic function pointer inside the guard. See the Objtool warnings > >> section #9 in the document tools/objtool/Documentation/objtool.txt. > >> > >> Considering that patching is usually small, replace the memcpy() and > >> memset() functions in the text poking functions with their open coded > >> versions. > >... > > > >Or just write a byte copy loop in C with (eg) barrier() inside it > >to stop gcc converting it to memcpy(). > > > > David > > Great. 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. David