x86/microcode: Clarify the late load logic

reload_store() is way too complicated. Split the inner workings out and
make the following enhancements:

 - Taint the kernel only when the microcode was actually updated. If. e.g.
   the rendezvous fails, then nothing happened and there is no reason for
   tainting.

 - Return useful error codes

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/r/20231002115903.145048840@linutronix.de

Author: KAGA-KOKO

arch/x86/kernel/cpu/microcode/core.c

@@ -362,11 +362,11 @@ static int microcode_reload_late(void)
 		pr_info("Reload succeeded, microcode revision: 0x%x -> 0x%x\n",
 			old, boot_cpu_data.microcode);
 		microcode_check(&prev_info);
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
 	} else {
 		pr_info("Reload failed, current microcode revision: 0x%x\n",
 			boot_cpu_data.microcode);
 	}
-
 	return ret;
 }
 
@@ -399,40 +399,37 @@ static bool ensure_cpus_are_online(void)
 	return true;
 }
 
+static int ucode_load_late_locked(void)
+{
+	if (!ensure_cpus_are_online())
+		return -EBUSY;
+
+	switch (microcode_ops->request_microcode_fw(0, &microcode_pdev->dev)) {
+	case UCODE_NEW:
+		return microcode_reload_late();
+	case UCODE_NFOUND:
+		return -ENOENT;
+	default:
+		return -EBADFD;
+	}
+}
+
 static ssize_t reload_store(struct device *dev,
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
-	enum ucode_state tmp_ret = UCODE_OK;
-	int bsp = boot_cpu_data.cpu_index;
 	unsigned long val;
-	ssize_t ret = 0;
+	ssize_t ret;
 
 	ret = kstrtoul(buf, 0, &val);
 	if (ret || val != 1)
 		return -EINVAL;
 
 	cpus_read_lock();
-
-	if (!ensure_cpus_are_online()) {
-		ret = -EBUSY;
-		goto put;
-	}
-
-	tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
-	if (tmp_ret != UCODE_NEW)
-		goto put;
-
-	ret = microcode_reload_late();
-put:
+	ret = ucode_load_late_locked();
 	cpus_read_unlock();
 
-	if (ret == 0)
-		ret = size;
-
-	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
-
-	return ret;
+	return ret ? : size;
 }
 
 static DEVICE_ATTR_WO(reload);