linux-kernel - [PATCH 9/9] Documentation/microcode: Document some aspects for more clarity

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Date:	Mon,  6 Jun 2016 17:10:50 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	X86 ML <x86@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 9/9] Documentation/microcode: Document some aspects for more clarity

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

Document that builtin microcode is 64-bit only. Also, improve/add
comments to places.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: linux-doc@...r.kernel.org
---
 Documentation/x86/early-microcode.txt |  5 ++++-
 arch/x86/kernel/cpu/microcode/intel.c | 16 +++++++++-------
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/Documentation/x86/early-microcode.txt b/Documentation/x86/early-microcode.txt
index c956d99cf1de..07749e7f3d50 100644
--- a/Documentation/x86/early-microcode.txt
+++ b/Documentation/x86/early-microcode.txt
@@ -45,7 +45,10 @@ Builtin microcode
 =================
 
 We can also load builtin microcode supplied through the regular firmware
-builtin method CONFIG_FIRMWARE_IN_KERNEL. Here's an example:
+builtin method CONFIG_FIRMWARE_IN_KERNEL. Only 64-bit is currently
+supported.
+
+Here's an example:
 
 CONFIG_FIRMWARE_IN_KERNEL=y
 CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 359e2034b558..8962d6acee39 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -40,9 +40,13 @@
 #include <asm/msr.h>
 
 /*
- * Temporary microcode blobs pointers storage. We note here the pointers to
- * microcode blobs we've got from whatever storage (detached initrd, builtin).
- * Later on, we put those into final storage mc_saved_data.mc_saved.
+ * Temporary microcode blobs pointers storage. We note here during early load
+ * the pointers to microcode blobs we've got from whatever storage (detached
+ * initrd, builtin). Later on, we put those into final storage
+ * mc_saved_data.mc_saved.
+ *
+ * Important: those are offsets from the beginning of initrd or absolute
+ * addresses within the kernel image when built-in.
  */
 static unsigned long mc_tmp_ptrs[MAX_UCODE_COUNT];
 
@@ -57,6 +61,7 @@ static struct ucode_blobs {
 	bool valid;
 } blobs;
 
+/* Go through saved patches and find the one suitable for the current CPU. */
 static enum ucode_state
 find_microcode_patch(struct microcode_intel **saved,
 		     unsigned int num_saved, struct ucode_cpu_info *uci)
@@ -466,6 +471,7 @@ static void show_saved_mc(void)
 static void save_mc_for_early(u8 *mc)
 {
 #ifdef CONFIG_HOTPLUG_CPU
+	/* Synchronization during CPU hotplug. */
 	static DEFINE_MUTEX(x86_cpu_microcode_mutex);
 
 	struct microcode_intel *mc_saved_tmp[MAX_UCODE_COUNT];
@@ -474,10 +480,6 @@ static void save_mc_for_early(u8 *mc)
 	struct microcode_intel **mc_saved;
 	int ret, i;
 
-	/*
-	 * Hold hotplug lock so mc_saved_data is not accessed by a CPU in
-	 * hotplug.
-	 */
 	mutex_lock(&x86_cpu_microcode_mutex);
 
 	mc_saved_count_init = mc_saved_data.num_saved;
-- 
2.7.3