Merge branch 'core/speculation' of git://git.kernel.org/pub/scm/linux/kernel/git...

[sfrench/cifs-2.6.git] / kernel / cpu.c

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 025f419d16f68be3e70cfcbdabe113ed655af6e4..43e741e88691c2993de99c50ad3e4031bac91ec9 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -564,6 +564,20 @@ static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
                cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
 }
 
+static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
+{
+       if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+               return true;
+       /*
+        * When CPU hotplug is disabled, then taking the CPU down is not
+        * possible because takedown_cpu() and the architecture and
+        * subsystem specific mechanisms are not available. So the CPU
+        * which would be completely unplugged again needs to stay around
+        * in the current state.
+        */
+       return st->state <= CPUHP_BRINGUP_CPU;
+}
+
 static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                              enum cpuhp_state target)
 {
@@ -574,8 +588,10 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                st->state++;
                ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
                if (ret) {
-                       st->target = prev_state;
-                       undo_cpu_up(cpu, st);
+                       if (can_rollback_cpu(st)) {
+                               st->target = prev_state;
+                               undo_cpu_up(cpu, st);
+                       }
                        break;
                }
        }
@@ -2288,3 +2304,18 @@ void __init boot_cpu_hotplug_init(void)
 #endif
        this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
 }
+
+enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO;
+
+static int __init mitigations_parse_cmdline(char *arg)
+{
+       if (!strcmp(arg, "off"))
+               cpu_mitigations = CPU_MITIGATIONS_OFF;
+       else if (!strcmp(arg, "auto"))
+               cpu_mitigations = CPU_MITIGATIONS_AUTO;
+       else if (!strcmp(arg, "auto,nosmt"))
+               cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
+
+       return 0;
+}
+early_param("mitigations", mitigations_parse_cmdline);