x86/microcode: Allow late microcode loading with SMT disabled

The kernel unnecessarily prevents late microcode loading when SMT is disabled. It should be safe to allow it if all the primary threads are online. Signed-off-by: Josh Poimboeuf <[email protected]> Acked-by: Borislav Petkov <[email protected]> Signed-off-by: David Woodhouse <[email protected]>
ambv · Aug 10, 2018 · 07d981a · 07d981a
1 parent e24f14b
commit 07d981a
Showing 1 changed file with 12 additions and 4 deletions.
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
@@ -509,12 +509,20 @@ static struct platform_device	*microcode_pdev;
 
 static int check_online_cpus(void)
 {
-	if (num_online_cpus() == num_present_cpus())
-		return 0;
+	unsigned int cpu;
 
-	pr_err("Not all CPUs online, aborting microcode update.\n");
+	/*
+	 * Make sure all CPUs are online.  It's fine for SMT to be disabled if
+	 * all the primary threads are still online.
+	 */
+	for_each_present_cpu(cpu) {
+		if (topology_is_primary_thread(cpu) && !cpu_online(cpu)) {
+			pr_err("Not all CPUs online, aborting microcode update.\n");
+			return -EINVAL;
+		}
+	}
 
-	return -EINVAL;
+	return 0;
 }
 
 static atomic_t late_cpus_in;