[PATCH v7 18/31] x86/speculation/mds: Mark cpu_buf_idle_clear key as allowed in .noinstr

[Valentin Schneider]

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 <vschneid at redhat.com>
---
 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