From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Fri, 10 Aug 2018 08:31:10 +0100
Subject: x86/microcode: Allow late microcode loading with SMT disabled
Git-commit: 07d981ad4cf1e78361c6db1c28ee5ba105f96cc1
Patch-mainline: v4.19-rc1
References: bsc#1110006

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>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/cpu/microcode/core.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -489,12 +489,20 @@ static struct platform_device	*microcode
 
 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;