x86/microcode: Run the AP-loading routine only on the application pro…

…cessors

cpu_init() is run also on the BSP (in addition to the APs):

 x86_64_start_kernel
 |-> x86_64_start_reservations
 |-> start_kernel
 |-> trap_init
 |-> cpu_init
 |-> load_ucode_ap
 ...

but we run the AP (Application Processors) microcode loading routine
there too even though we have a BSP-specific routine for that:
load_ucode_bsp().

Which is unnecessary. So let's limit the AP microcode loading routine to
the APs only.

Remove a useless comment while at it.

Signed-off-by: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/kernel/cpu/common.c

@@ -1462,11 +1462,8 @@ void cpu_init(void)
 	 */
 	cr4_init_shadow();
 
-	/*
-	 * Load microcode on this cpu if a valid microcode is available.
-	 * This is early microcode loading procedure.
-	 */
-	load_ucode_ap();
+	if (cpu)
+		load_ucode_ap();
 
 	t = &per_cpu(cpu_tss, cpu);
 	oist = &per_cpu(orig_ist, cpu);

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

@@ -357,17 +357,12 @@ static void __init get_bsp_sig(void)
 #else
 void load_ucode_amd_ap(void)
 {
-	unsigned int cpu = smp_processor_id();
 	struct equiv_cpu_entry *eq;
 	struct microcode_amd *mc;
 	u8 *cont = container;
 	u32 rev, eax;
 	u16 eq_id;
 
-	/* Exit if called on the BSP. */
-	if (!cpu)
-		return;
-
 	if (!container)
 		return;