linux-kernel - [PATCH 01/12] x86/microcode: Run the AP-loading routine only on the application processors

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Message-Id: <20161025095522.11964-2-bp@alien8.de>
Date:   Tue, 25 Oct 2016 11:55:11 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 01/12] x86/microcode: Run the AP-loading routine only on the application processors

From: Borislav Petkov <bp@...e.de>

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 <bp@...e.de>
---
 arch/x86/kernel/cpu/common.c        | 7 ++-----
 arch/x86/kernel/cpu/microcode/amd.c | 5 -----
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9bd910a7dd0a..1a1d668263b9 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/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);
diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 620ab06bcf45..6b3929e80fd4 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/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;
 
-- 
2.10.0