linux-kernel - [RFC PATCH v3 07/15] x86/speculation/mds: Make mds_idle

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Message-ID: <20241119153502.41361-8-vschneid@redhat.com>
Date: Tue, 19 Nov 2024 16:34:54 +0100
From: Valentin Schneider <vschneid@...hat.com>
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	linux-doc@...r.kernel.org,
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Subject: [RFC PATCH v3 07/15] x86/speculation/mds: Make mds_idle_clear forceful

Later commits will cause objtool to warn about non __ro_after_init 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 as forceful to let the kernel know to always send the
text_poke_sync() IPI for it, and 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 47a01d4028f60..dcc4d5d6e3b95 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -114,7 +114,7 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
 DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
 
 /* Control MDS CPU buffer clear before idling (halt, mwait) */
-DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
+DEFINE_STATIC_KEY_FALSE_FORCE(mds_idle_clear);
 EXPORT_SYMBOL_GPL(mds_idle_clear);
 
 /*
-- 
2.43.0