x86/microcode: Default-disable late loading

[ Upstream commit a77a94f86273ce42a39cb479217dd8d68acfe0ff ]

It is dangerous and it should not be used anyway - there's a nice early
loading already.

Requested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-3-bp@alien8.de
Stable-dep-of: c0dd9245aa9e ("x86/microcode: Check CPU capabilities after late microcode update correctly")
Signed-off-by: Sasha Levin <sashal@kernel.org>

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

@@ -393,6 +393,7 @@ static int apply_microcode_on_target(int cpu)
 /* fake device for request_firmware */
 static struct platform_device	*microcode_pdev;
 
+#ifdef CONFIG_MICROCODE_LATE_LOADING
 /*
  * Late loading dance. Why the heavy-handed stomp_machine effort?
  *
@@ -560,6 +561,9 @@ put:
 	return ret;
 }
 
+static DEVICE_ATTR_WO(reload);
+#endif
+
 static ssize_t version_show(struct device *dev,
 			struct device_attribute *attr, char *buf)
 {
@@ -576,7 +580,6 @@ static ssize_t pf_show(struct device *dev,
 	return sprintf(buf, "0x%x\n", uci->cpu_sig.pf);
 }
 
-static DEVICE_ATTR_WO(reload);
 static DEVICE_ATTR(version, 0444, version_show, NULL);
 static DEVICE_ATTR(processor_flags, 0444, pf_show, NULL);
 
@@ -729,7 +732,9 @@ static int mc_cpu_down_prep(unsigned int cpu)
 }
 
 static struct attribute *cpu_root_microcode_attrs[] = {
+#ifdef CONFIG_MICROCODE_LATE_LOADING
 	&dev_attr_reload.attr,
+#endif
 	NULL
 };