[PATCH RFC 4/7] x86: cpu: bugs.c: update cpu_smt_disable to be callable at runtime

[Mihai Carabas]

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.cara...@oracle.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