x86/microcode: Allow late microcode loading with SMT disabled

commit 07d981ad4cf1e78361c6db1c28ee5ba105f96cc1 upstream

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 4fc0e08a30b9981faf809132ef74a129bd1572a1..387a8f44fba1ecca7436e2cf2ae6b0cdbb43977f 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;