linux-kernel - [PATCH RFC 4/7] x86: cpu: bugs.c: update cpu_smt

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Date:   Thu,  2 Jul 2020 18:18:24 +0300
From:   Mihai Carabas <mihai.carabas@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Mihai Carabas <mihai.carabas@...cle.com>
Subject: [PATCH RFC 4/7] x86: cpu: bugs.c: update cpu_smt_disable to be callable at runtime

If the microcode late loading and bug mitigation logic needs to turn
off SMT, it must use the hot plug infrastructure, not the boot time call
"cpu_smt_disable".

Update "cpu_smt_disable" to use the hot plug infrastructure to turn off
SMT when the system is in state running.

Signed-off-by: Mihai Carabas <mihai.carabas@...cle.com>
---
 kernel/cpu.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index fe67a01..719670f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -393,9 +393,25 @@ void __weak arch_smt_update(void) { }
 
 void cpu_smt_disable(bool force)
 {
+	int ret;
+
 	if (!cpu_smt_possible())
 		return;
 
+	if (system_state == SYSTEM_RUNNING) {
+		if (force)
+			ret = cpuhp_smt_disable(CPU_SMT_FORCE_DISABLED);
+		else
+			ret = cpuhp_smt_disable(CPU_SMT_DISABLED);
+
+		/* If SMT disable did not succeed, print a warning*/
+		if (ret)
+			pr_warn("SMT: not disabled %d\n", ret);
+		else
+			pr_info("SMT:%s disabled\n", force ? " Force" : "");
+		return;
+	}
+
 	if (force) {
 		pr_info("SMT: Force disabled\n");
 		cpu_smt_control = CPU_SMT_FORCE_DISABLED;
-- 
1.8.3.1