x86/microcode: Extend post microcode reload to support IBPB feature

CVE-2017-5715 (Spectre v2 Intel)

Add an IBPB feature check to the speculative control update check after
a microcode reload.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(backported from commit 073bee2caa42ddde1134cb87c955b4cad7b7d38b)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

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

@@ -430,6 +430,13 @@ static ssize_t reload_store(struct device *dev,
 		if (ibpb_inuse)
 			sysctl_ibpb_enabled = 1;
 		mutex_unlock(&spec_ctrl_mutex);
+	} else if (boot_cpu_has(X86_FEATURE_IBPB)) {
+		printk_once(KERN_INFO "FEATURE IBPB Present\n");
+		mutex_lock(&spec_ctrl_mutex);
+		set_ibpb_supported();
+		if (ibpb_inuse)
+			sysctl_ibpb_enabled = 1;
+		mutex_unlock(&spec_ctrl_mutex);
 	}
 
 	mutex_unlock(&microcode_mutex);