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 <jpoimboe@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 08286269fd2411799304a9a5f004615111674b12..b9bc8a1a584e39590e7beecdafb47773015794f7 100644 (file)
--- 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;