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Peter Anvin" To: David Laight , "Kirill A. Shutemov" CC: 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: =?US-ASCII?Q?Re=3A_=5BPATCHv9_02/16=5D_x86/alternatives=3A_Disa?= =?US-ASCII?Q?ble_LASS_when_patching_kernel_alternatives?= User-Agent: K-9 Mail for Android In-Reply-To: <20250728201137.113d0f45@pumpkin> References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> <20250728201137.113d0f45@pumpkin> Message-ID: <98BE7799-DA6C-4267-9E03-E6F68263D250@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: s4hjptabk4ptx5by156p1bf617o6jxtz X-Rspamd-Queue-Id: 94AEBC0007 X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1753730993-216965 X-HE-Meta: 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 8EyYT3e6 KJdo6H6GoAJ6SAJvdJ7JjDTfWrvcHvjIdEQhw8Q4o20jinFRAYdgF4bk5XfpmsuKwlZ4rPmHQ3vG71oZzUFGvOIKebjQD1AqChQpvevs46+TCJMUwzMkg8EcPze5A+dVZDwvLAs4S8lKzmPgrjzS7tkr7FULSDLG7+gxARAfmvQSy2AFyMJG1/g32CDOQgKcGJ3+c6UHR7l1I6SUtxf9rwwbOUXykKlHZdKa4BT959be1UUwEW14Nh58tzVlXB0fO+Z3HU02FH/ZieUV5WzXQ0NVOJJ1762WGfENr9MbzxCfYITAggr9FDlKOvlDZuTXkp6eh+HdCdTzddQz+YywGPQofQZ/goCUhtDlfRr3MZLvBHJvli7M8Utwbt3CUnReCXBJ/6Fh6Aqnoo5Ax1VFf3Dw7HJu4Qr5VuFvLIKCWQVz3gTtJHG7hS48Uljvrt1hovsJEdkIrdjSVKKODReEmNwZbv7iG2HU/FyRe 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 July 28, 2025 12:11:37 PM PDT, David Laight wrote: >On Mon, 7 Jul 2025 11:03:02 +0300 >"Kirill A=2E Shutemov" wrote: > >> From: Sohil Mehta >>=20 >> For patching, the kernel initializes a temporary mm area in the lower >> half of the address range=2E See commit 4fc19708b165 ("x86/alternatives= : >> Initialize temporary mm for patching")=2E >>=20 >> Disable LASS enforcement during patching to avoid triggering a #GP >> fault=2E >>=20 >> 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=2E See the Objtool warnings >> section #9 in the document tools/objtool/Documentation/objtool=2Etxt=2E >>=20 >> Considering that patching is usually small, replace the memcpy() and >> memset() functions in the text poking functions with their open coded >> versions=2E >=2E=2E=2E > >Or just write a byte copy loop in C with (eg) barrier() inside it >to stop gcc converting it to memcpy()=2E > > David Great=2E It's rep movsb without any of the performance=2E