6 files changed, 22 insertions, 5 deletions

diff --git a/src/cpu/intel/model_1067x/mp_init.c b/src/cpu/intel/model_1067x/mp_init.c
index b56d106922..ff6cbec8dc 100644
--- a/src/cpu/intel/model_1067x/mp_init.c
+++ b/src/cpu/intel/model_1067x/mp_init.c
@@ -33,7 +33,7 @@ static int get_cpu_count(void)
 static void get_microcode_info(const void **microcode, int *parallel)
 {
 	*microcode = microcode_patch;
-	*parallel = 1;
+	*parallel = !intel_ht_supported();
 }
 
 /* the SMRR enable and lock bit need to be set in IA32_FEATURE_CONTROL
diff --git a/src/cpu/intel/model_2065x/model_2065x_init.c b/src/cpu/intel/model_2065x/model_2065x_init.c
index db433536cf..88e42a5051 100644
--- a/src/cpu/intel/model_2065x/model_2065x_init.c
+++ b/src/cpu/intel/model_2065x/model_2065x_init.c
@@ -251,7 +251,7 @@ static void get_microcode_info(const void **microcode, int *parallel)
 {
 	microcode_patch = intel_microcode_find();
 	*microcode = microcode_patch;
-	*parallel = 1;
+	*parallel = !intel_ht_supported();
 }
 
 static void per_cpu_smm_trigger(void)
diff --git a/src/cpu/intel/model_206ax/model_206ax_init.c b/src/cpu/intel/model_206ax/model_206ax_init.c
index 2afbfeecec..b08a86fba2 100644
--- a/src/cpu/intel/model_206ax/model_206ax_init.c
+++ b/src/cpu/intel/model_206ax/model_206ax_init.c
@@ -497,7 +497,7 @@ static void get_microcode_info(const void **microcode, int *parallel)
 {
 	microcode_patch = intel_microcode_find();
 	*microcode = microcode_patch;
-	*parallel = 1;
+	*parallel = !intel_ht_supported();
 }
 
 static void per_cpu_smm_trigger(void)
diff --git a/src/cpu/x86/sipi_vector.S b/src/cpu/x86/sipi_vector.S
index 02ad0d367a..e1b90890ed 100644
--- a/src/cpu/x86/sipi_vector.S
+++ b/src/cpu/x86/sipi_vector.S
@@ -102,6 +102,13 @@ _start:
 	/* Save CPU number. */
 	mov	%ecx, %esi
 
+	/*
+	 * The following code only needs to run on Intel platforms and thus the caller
+	 * doesn't provide a microcode_ptr if not on Intel.
+	 * On Intel platforms which update microcode using FIT the version check will
+	 * also skip the microcode update.
+	 */
+
 	/* Determine if one should check microcode versions. */
 	mov	microcode_ptr, %edi
 	test	%edi, %edi
@@ -116,6 +123,16 @@ _start:
 	test	%edx, %edx
 	jnz	microcode_done
 
+	/*
+	 * Intel SDM and various BWGs specify to use a semaphore to update microcode
+	 * on one thread per core on Hyper-Threading enabled CPUs. Due to this complex
+	 * code would be necessary to determine the core #ID, initializing and picking
+	 * the right semaphore out of CONFIG_MAX_CPUS / 2.
+	 * Instead of the per core approachm, as recommended, use one global spinlock.
+	 * Assuming that only pre-FIT platforms with Hyper-Threading enabled and at
+	 * most 8 threads will ever run into this condition, the boot delay is negligible.
+	 */
+
 	/* Determine if parallel microcode loading is allowed. */
 	cmpl	$0xffffffff, microcode_lock
 	je	load_microcode
diff --git a/src/soc/intel/baytrail/cpu.c b/src/soc/intel/baytrail/cpu.c
index 2029017e1f..e624240d92 100644
--- a/src/soc/intel/baytrail/cpu.c
+++ b/src/soc/intel/baytrail/cpu.c
@@ -149,7 +149,7 @@ static void get_microcode_info(const void **microcode, int *parallel)
 	const struct pattrs *pattrs = pattrs_get();
 
 	*microcode = pattrs->microcode_patch;
-	*parallel = 1;
+	*parallel = !intel_ht_supported();
 }
 
 static void per_cpu_smm_trigger(void)
diff --git a/src/soc/intel/braswell/cpu.c b/src/soc/intel/braswell/cpu.c
index 04bf1082c3..0c6f463438 100644
--- a/src/soc/intel/braswell/cpu.c
+++ b/src/soc/intel/braswell/cpu.c
@@ -152,7 +152,7 @@ static void get_microcode_info(const void **microcode, int *parallel)
 	const struct pattrs *pattrs = pattrs_get();
 
 	*microcode = pattrs->microcode_patch;
-	*parallel = 1;
+	*parallel = !intel_ht_supported();
 }
 
 static void per_cpu_smm_trigger(void)