linux-kernel - [PATCH v5 17/25] x86/speculation/mds: Mark mds_idle

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Message-ID: <20250429113242.998312-18-vschneid@redhat.com>
Date: Tue, 29 Apr 2025 13:32:34 +0200
From: Valentin Schneider <vschneid@...hat.com>
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Subject: [PATCH v5 17/25] x86/speculation/mds: Mark mds_idle_clear key as allowed in .noinstr

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.

mds_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 <vschneid@...hat.com>
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 362602b705cc4..59a77ca1bb14c 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -117,7 +117,7 @@ DEFINE_STATIC_KEY_FALSE(switch_vcpu_ibpb);
 EXPORT_SYMBOL_GPL(switch_vcpu_ibpb);
 
 /* Control MDS CPU buffer clear before idling (halt, mwait) */
-DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
+DEFINE_STATIC_KEY_FALSE_NOINSTR(mds_idle_clear);
 EXPORT_SYMBOL_GPL(mds_idle_clear);
 
 /*
-- 
2.49.0