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Fri, 14 Nov 2025 15:06:40 +0000 (UTC) Received: from vschneid-thinkpadt14sgen2i.remote.csb (unknown [10.45.226.10]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BF9A91956048; Fri, 14 Nov 2025 15:06:26 +0000 (UTC) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Josh Poimboeuf , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Juri Lelli , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner , Petr Tesarik , Shrikanth Hegde Subject: [PATCH v7 18/31] x86/speculation/mds: Mark cpu_buf_idle_clear key as allowed in .noinstr Date: Fri, 14 Nov 2025 16:01:20 +0100 Message-ID: <20251114150133.1056710-19-vschneid@redhat.com> In-Reply-To: <20251114150133.1056710-1-vschneid@redhat.com> References: <20251114150133.1056710-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251114_141127_379879_AE0F6F91 X-CRM114-Status: GOOD ( 13.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Later commits will cause objtool to warn about static keys being used in .noinstr sections in order to safely defer instruction patching IPIs targeted at NOHZ_FULL CPUs. cpu_buf_idle_clear is used in .noinstr code, and can be modified at runtime (SMT hotplug). Suppressing the text_poke_sync() IPI has little benefits for this key, as hotplug implies eventually going through takedown_cpu() -> stop_machine_cpuslocked() which is going to cause interference on all online CPUs anyway. Mark it to let objtool know not to warn about it. Signed-off-by: Valentin Schneider --- arch/x86/kernel/cpu/bugs.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index a2d7dc4d2a4a3..39f6a2f9593f8 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -181,8 +181,13 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); DEFINE_STATIC_KEY_FALSE(switch_vcpu_ibpb); EXPORT_SYMBOL_GPL(switch_vcpu_ibpb); -/* Control CPU buffer clear before idling (halt, mwait) */ -DEFINE_STATIC_KEY_FALSE(cpu_buf_idle_clear); +/* + * Control CPU buffer clear before idling (halt, mwait) + * + * NOINSTR: This static key is updated during SMT hotplug which itself already + * causes some interference. + */ +DEFINE_STATIC_KEY_FALSE_NOINSTR(cpu_buf_idle_clear); EXPORT_SYMBOL_GPL(cpu_buf_idle_clear); /* -- 2.51.0