cpu/x86/mp_init.c: Add mp_run_on_all_cpus_synchronously

MTRR is a core level register which means 2 threads in one core share
same MTRR. There is a race condition could happen that AP overrides
BSP MTRR unintentionally.

In order to prevent such race condition between BSP and APs, this
patch provides a function to let BSP assign tasks to all APs and wait
them to complete the assigned tasks.

BUG=b:225766934

Change-Id: I8d1d49bca410c821a3ad0347548afc42eb860594
Signed-off-by: Kane Chen <kane.chen@intel.corp-partner.google.com>
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63566
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/x86/mp_init.c

@@ -859,6 +859,15 @@ static void trigger_smm_relocation(void)
 
 static struct mp_callback *ap_callbacks[CONFIG_MAX_CPUS];
 
+enum AP_STATUS {
+	/* AP takes the task but not yet finishes */
+	AP_BUSY = 1,
+	/* AP finishes the task or no task to run yet */
+	AP_NOT_BUSY
+};
+
+static atomic_t ap_status[CONFIG_MAX_CPUS];
+
 static struct mp_callback *read_callback(struct mp_callback **slot)
 {
 	struct mp_callback *ret;
@@ -880,10 +889,10 @@ static void store_callback(struct mp_callback **slot, struct mp_callback *val)
 	);
 }
 
-static enum cb_err run_ap_work(struct mp_callback *val, long expire_us)
+static enum cb_err run_ap_work(struct mp_callback *val, long expire_us, bool wait_ap_finish)
 {
 	int i;
-	int cpus_accepted;
+	int cpus_accepted, cpus_finish;
 	struct stopwatch sw;
 	int cur_cpu;
 
@@ -913,16 +922,28 @@ static enum cb_err run_ap_work(struct mp_callback *val, long expire_us)
 
 	do {
 		cpus_accepted = 0;
+		cpus_finish = 0;
 
 		for (i = 0; i < ARRAY_SIZE(ap_callbacks); i++) {
 			if (cur_cpu == i)
 				continue;
-			if (read_callback(&ap_callbacks[i]) == NULL)
+
+			if (read_callback(&ap_callbacks[i]) == NULL) {
 				cpus_accepted++;
+				/* Only increase cpus_finish if AP took the task and not busy */
+				if (atomic_read(&ap_status[i]) == AP_NOT_BUSY)
+					cpus_finish++;
+			}
 		}
 
+		/*
+		 * if wait_ap_finish is true, need to make sure all CPUs finish task and return
+		 * else just need to make sure all CPUs take task
+		 */
 		if (cpus_accepted == global_num_aps)
-			return CB_SUCCESS;
+			if (!wait_ap_finish || (cpus_finish == global_num_aps))
+				return CB_SUCCESS;
+
 	} while (expire_us <= 0 || !stopwatch_expired(&sw));
 
 	printk(BIOS_CRIT, "CRITICAL ERROR: AP call expired. %d/%d CPUs accepted.\n",
@@ -948,6 +969,9 @@ static void ap_wait_for_instruction(void)
 
 	per_cpu_slot = &ap_callbacks[cur_cpu];
 
+	/* Init ap_status[cur_cpu] to AP_NOT_BUSY and ready to take job */
+	atomic_set(&ap_status[cur_cpu], AP_NOT_BUSY);
+
 	while (1) {
 		struct mp_callback *cb = read_callback(per_cpu_slot);
 
@@ -955,16 +979,22 @@ static void ap_wait_for_instruction(void)
 			asm ("pause");
 			continue;
 		}
+		/*
+		 * Set ap_status to AP_BUSY before store_callback(per_cpu_slot, NULL).
+		 * it's to let BSP know APs take tasks and busy to avoid race condition.
+		 */
+		atomic_set(&ap_status[cur_cpu], AP_BUSY);
 
 		/* Copy to local variable before signaling consumption. */
 		memcpy(&lcb, cb, sizeof(lcb));
 		mfence();
 		store_callback(per_cpu_slot, NULL);
-		if (lcb.logical_cpu_number && (cur_cpu !=
+
-				lcb.logical_cpu_number))
+		if (lcb.logical_cpu_number == MP_RUN_ON_ALL_CPUS ||
-			continue;
+				(cur_cpu == lcb.logical_cpu_number))
-		else
 			lcb.func(lcb.arg);
+
+		atomic_set(&ap_status[cur_cpu], AP_NOT_BUSY);
 	}
 }
 
@@ -973,7 +1003,15 @@ enum cb_err mp_run_on_aps(void (*func)(void *), void *arg, int logical_cpu_num,
 {
 	struct mp_callback lcb = { .func = func, .arg = arg,
 				.logical_cpu_number = logical_cpu_num};
-	return run_ap_work(&lcb, expire_us);
+	return run_ap_work(&lcb, expire_us, false);
+}
+
+static enum cb_err mp_run_on_aps_and_wait_for_complete(void (*func)(void *), void *arg,
+		int logical_cpu_num, long expire_us)
+{
+	struct mp_callback lcb = { .func = func, .arg = arg,
+				.logical_cpu_number = logical_cpu_num};
+	return run_ap_work(&lcb, expire_us, true);
 }
 
 enum cb_err mp_run_on_all_aps(void (*func)(void *), void *arg, long expire_us,
@@ -1008,6 +1046,16 @@ enum cb_err mp_run_on_all_cpus(void (*func)(void *), void *arg)
 	return mp_run_on_aps(func, arg, MP_RUN_ON_ALL_CPUS, 1000 * USECS_PER_MSEC);
 }
 
+enum cb_err mp_run_on_all_cpus_synchronously(void (*func)(void *), void *arg)
+{
+	/* Run on BSP first. */
+	func(arg);
+
+	/* For up to 1 second for AP to finish previous work. */
+	return mp_run_on_aps_and_wait_for_complete(func, arg, MP_RUN_ON_ALL_CPUS,
+						1000 * USECS_PER_MSEC);
+}
+
 enum cb_err mp_park_aps(void)
 {
 	struct stopwatch sw;

src/include/cpu/x86/mp.h

@@ -117,6 +117,10 @@ enum cb_err mp_run_on_all_aps(void (*func)(void *), void *arg, long expire_us,
 /* Like mp_run_on_aps() but also runs func on BSP. */
 enum cb_err mp_run_on_all_cpus(void (*func)(void *), void *arg);
 
+/* Like mp_run_on_all_cpus but make sure all APs finish executing the
+   function call. The time limit on a function call is 1 second. */
+enum cb_err mp_run_on_all_cpus_synchronously(void (*func)(void *), void *arg);
+
 /*
  * Park all APs to prepare for OS boot. This is handled automatically
  * by the coreboot infrastructure.