1 files changed, 528 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
new file mode 100644
index 0000000000..1123ef3ccf
--- /dev/null
+++ b/arch/x86/kernel/tsc_sync.c
@@ -0,0 +1,528 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * check TSC synchronization.
+ *
+ * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
+ *
+ * We check whether all boot CPUs have their TSC's synchronized,
+ * print a warning if not and turn off the TSC clock-source.
+ *
+ * The warp-check is point-to-point between two CPUs, the CPU
+ * initiating the bootup is the 'source CPU', the freshly booting
+ * CPU is the 'target CPU'.
+ *
+ * Only two CPUs may participate - they can enter in any order.
+ * ( The serial nature of the boot logic and the CPU hotplug lock
+ *   protects against more than 2 CPUs entering this code. )
+ */
+#include <linux/workqueue.h>
+#include <linux/topology.h>
+#include <linux/spinlock.h>
+#include <linux/kernel.h>
+#include <linux/smp.h>
+#include <linux/nmi.h>
+#include <asm/tsc.h>
+
+struct tsc_adjust {
+	s64		bootval;
+	s64		adjusted;
+	unsigned long	nextcheck;
+	bool		warned;
+};
+
+static DEFINE_PER_CPU(struct tsc_adjust, tsc_adjust);
+static struct timer_list tsc_sync_check_timer;
+
+/*
+ * TSC's on different sockets may be reset asynchronously.
+ * This may cause the TSC ADJUST value on socket 0 to be NOT 0.
+ */
+bool __read_mostly tsc_async_resets;
+
+void mark_tsc_async_resets(char *reason)
+{
+	if (tsc_async_resets)
+		return;
+	tsc_async_resets = true;
+	pr_info("tsc: Marking TSC async resets true due to %s\n", reason);
+}
+
+void tsc_verify_tsc_adjust(bool resume)
+{
+	struct tsc_adjust *adj = this_cpu_ptr(&tsc_adjust);
+	s64 curval;
+
+	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
+		return;
+
+	/* Skip unnecessary error messages if TSC already unstable */
+	if (check_tsc_unstable())
+		return;
+
+	/* Rate limit the MSR check */
+	if (!resume && time_before(jiffies, adj->nextcheck))
+		return;
+
+	adj->nextcheck = jiffies + HZ;
+
+	rdmsrl(MSR_IA32_TSC_ADJUST, curval);
+	if (adj->adjusted == curval)
+		return;
+
+	/* Restore the original value */
+	wrmsrl(MSR_IA32_TSC_ADJUST, adj->adjusted);
+
+	if (!adj->warned || resume) {
+		pr_warn(FW_BUG "TSC ADJUST differs: CPU%u %lld --> %lld. Restoring\n",
+			smp_processor_id(), adj->adjusted, curval);
+		adj->warned = true;
+	}
+}
+
+/*
+ * Normally the tsc_sync will be checked every time system enters idle
+ * state, but there is still caveat that a system won't enter idle,
+ * either because it's too busy or configured purposely to not enter
+ * idle.
+ *
+ * So setup a periodic timer (every 10 minutes) to make sure the check
+ * is always on.
+ */
+
+#define SYNC_CHECK_INTERVAL		(HZ * 600)
+
+static void tsc_sync_check_timer_fn(struct timer_list *unused)
+{
+	int next_cpu;
+
+	tsc_verify_tsc_adjust(false);
+
+	/* Run the check for all onlined CPUs in turn */
+	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+	if (next_cpu >= nr_cpu_ids)
+		next_cpu = cpumask_first(cpu_online_mask);
+
+	tsc_sync_check_timer.expires += SYNC_CHECK_INTERVAL;
+	add_timer_on(&tsc_sync_check_timer, next_cpu);
+}
+
+static int __init start_sync_check_timer(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_TSC_ADJUST) || tsc_clocksource_reliable)
+		return 0;
+
+	timer_setup(&tsc_sync_check_timer, tsc_sync_check_timer_fn, 0);
+	tsc_sync_check_timer.expires = jiffies + SYNC_CHECK_INTERVAL;
+	add_timer(&tsc_sync_check_timer);
+
+	return 0;
+}
+late_initcall(start_sync_check_timer);
+
+static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval,
+				   unsigned int cpu, bool bootcpu)
+{
+	/*
+	 * First online CPU in a package stores the boot value in the
+	 * adjustment value. This value might change later via the sync
+	 * mechanism. If that fails we still can yell about boot values not
+	 * being consistent.
+	 *
+	 * On the boot cpu we just force set the ADJUST value to 0 if it's
+	 * non zero. We don't do that on non boot cpus because physical
+	 * hotplug should have set the ADJUST register to a value > 0 so
+	 * the TSC is in sync with the already running cpus.
+	 *
+	 * Also don't force the ADJUST value to zero if that is a valid value
+	 * for socket 0 as determined by the system arch.  This is required
+	 * when multiple sockets are reset asynchronously with each other
+	 * and socket 0 may not have an TSC ADJUST value of 0.
+	 */
+	if (bootcpu && bootval != 0) {
+		if (likely(!tsc_async_resets)) {
+			pr_warn(FW_BUG "TSC ADJUST: CPU%u: %lld force to 0\n",
+				cpu, bootval);
+			wrmsrl(MSR_IA32_TSC_ADJUST, 0);
+			bootval = 0;
+		} else {
+			pr_info("TSC ADJUST: CPU%u: %lld NOT forced to 0\n",
+				cpu, bootval);
+		}
+	}
+	cur->adjusted = bootval;
+}
+
+#ifndef CONFIG_SMP
+bool __init tsc_store_and_check_tsc_adjust(bool bootcpu)
+{
+	struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust);
+	s64 bootval;
+
+	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
+		return false;
+
+	/* Skip unnecessary error messages if TSC already unstable */
+	if (check_tsc_unstable())
+		return false;
+
+	rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
+	cur->bootval = bootval;
+	cur->nextcheck = jiffies + HZ;
+	tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(), bootcpu);
+	return false;
+}
+
+#else /* !CONFIG_SMP */
+
+/*
+ * Store and check the TSC ADJUST MSR if available
+ */
+bool tsc_store_and_check_tsc_adjust(bool bootcpu)
+{
+	struct tsc_adjust *ref, *cur = this_cpu_ptr(&tsc_adjust);
+	unsigned int refcpu, cpu = smp_processor_id();
+	struct cpumask *mask;
+	s64 bootval;
+
+	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
+		return false;
+
+	rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
+	cur->bootval = bootval;
+	cur->nextcheck = jiffies + HZ;
+	cur->warned = false;
+
+	/*
+	 * If a non-zero TSC value for socket 0 may be valid then the default
+	 * adjusted value cannot assumed to be zero either.
+	 */
+	if (tsc_async_resets)
+		cur->adjusted = bootval;
+
+	/*
+	 * Check whether this CPU is the first in a package to come up. In
+	 * this case do not check the boot value against another package
+	 * because the new package might have been physically hotplugged,
+	 * where TSC_ADJUST is expected to be different. When called on the
+	 * boot CPU topology_core_cpumask() might not be available yet.
+	 */
+	mask = topology_core_cpumask(cpu);
+	refcpu = mask ? cpumask_any_but(mask, cpu) : nr_cpu_ids;
+
+	if (refcpu >= nr_cpu_ids) {
+		tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(),
+				       bootcpu);
+		return false;
+	}
+
+	ref = per_cpu_ptr(&tsc_adjust, refcpu);
+	/*
+	 * Compare the boot value and complain if it differs in the
+	 * package.
+	 */
+	if (bootval != ref->bootval)
+		printk_once(FW_BUG "TSC ADJUST differs within socket(s), fixing all errors\n");
+
+	/*
+	 * The TSC_ADJUST values in a package must be the same. If the boot
+	 * value on this newly upcoming CPU differs from the adjustment
+	 * value of the already online CPU in this package, set it to that
+	 * adjusted value.
+	 */
+	if (bootval != ref->adjusted) {
+		cur->adjusted = ref->adjusted;
+		wrmsrl(MSR_IA32_TSC_ADJUST, ref->adjusted);
+	}
+	/*
+	 * We have the TSCs forced to be in sync on this package. Skip sync
+	 * test:
+	 */
+	return true;
+}
+
+/*
+ * Entry/exit counters that make sure that both CPUs
+ * run the measurement code at once:
+ */
+static atomic_t start_count;
+static atomic_t stop_count;
+static atomic_t test_runs;
+
+/*
+ * We use a raw spinlock in this exceptional case, because
+ * we want to have the fastest, inlined, non-debug version
+ * of a critical section, to be able to prove TSC time-warps:
+ */
+static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED;
+
+static cycles_t last_tsc;
+static cycles_t max_warp;
+static int nr_warps;
+static int random_warps;
+
+/*
+ * TSC-warp measurement loop running on both CPUs.  This is not called
+ * if there is no TSC.
+ */
+static cycles_t check_tsc_warp(unsigned int timeout)
+{
+	cycles_t start, now, prev, end, cur_max_warp = 0;
+	int i, cur_warps = 0;
+
+	start = rdtsc_ordered();
+	/*
+	 * The measurement runs for 'timeout' msecs:
+	 */
+	end = start + (cycles_t) tsc_khz * timeout;
+
+	for (i = 0; ; i++) {
+		/*
+		 * We take the global lock, measure TSC, save the
+		 * previous TSC that was measured (possibly on
+		 * another CPU) and update the previous TSC timestamp.
+		 */
+		arch_spin_lock(&sync_lock);
+		prev = last_tsc;
+		now = rdtsc_ordered();
+		last_tsc = now;
+		arch_spin_unlock(&sync_lock);
+
+		/*
+		 * Be nice every now and then (and also check whether
+		 * measurement is done [we also insert a 10 million
+		 * loops safety exit, so we dont lock up in case the
+		 * TSC readout is totally broken]):
+		 */
+		if (unlikely(!(i & 7))) {
+			if (now > end || i > 10000000)
+				break;
+			cpu_relax();
+			touch_nmi_watchdog();
+		}
+		/*
+		 * Outside the critical section we can now see whether
+		 * we saw a time-warp of the TSC going backwards:
+		 */
+		if (unlikely(prev > now)) {
+			arch_spin_lock(&sync_lock);
+			max_warp = max(max_warp, prev - now);
+			cur_max_warp = max_warp;
+			/*
+			 * Check whether this bounces back and forth. Only
+			 * one CPU should observe time going backwards.
+			 */
+			if (cur_warps != nr_warps)
+				random_warps++;
+			nr_warps++;
+			cur_warps = nr_warps;
+			arch_spin_unlock(&sync_lock);
+		}
+	}
+	WARN(!(now-start),
+		"Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
+			now-start, end-start);
+	return cur_max_warp;
+}
+
+/*
+ * If the target CPU coming online doesn't have any of its core-siblings
+ * online, a timeout of 20msec will be used for the TSC-warp measurement
+ * loop. Otherwise a smaller timeout of 2msec will be used, as we have some
+ * information about this socket already (and this information grows as we
+ * have more and more logical-siblings in that socket).
+ *
+ * Ideally we should be able to skip the TSC sync check on the other
+ * core-siblings, if the first logical CPU in a socket passed the sync test.
+ * But as the TSC is per-logical CPU and can potentially be modified wrongly
+ * by the bios, TSC sync test for smaller duration should be able
+ * to catch such errors. Also this will catch the condition where all the
+ * cores in the socket don't get reset at the same time.
+ */
+static inline unsigned int loop_timeout(int cpu)
+{
+	return (cpumask_weight(topology_core_cpumask(cpu)) > 1) ? 2 : 20;
+}
+
+static void tsc_sync_mark_tsc_unstable(struct work_struct *work)
+{
+	mark_tsc_unstable("check_tsc_sync_source failed");
+}
+
+static DECLARE_WORK(tsc_sync_work, tsc_sync_mark_tsc_unstable);
+
+/*
+ * The freshly booted CPU initiates this via an async SMP function call.
+ */
+static void check_tsc_sync_source(void *__cpu)
+{
+	unsigned int cpu = (unsigned long)__cpu;
+	int cpus = 2;
+
+	/*
+	 * Set the maximum number of test runs to
+	 *  1 if the CPU does not provide the TSC_ADJUST MSR
+	 *  3 if the MSR is available, so the target can try to adjust
+	 */
+	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
+		atomic_set(&test_runs, 1);
+	else
+		atomic_set(&test_runs, 3);
+retry:
+	/* Wait for the target to start. */
+	while (atomic_read(&start_count) != cpus - 1)
+		cpu_relax();
+
+	/*
+	 * Trigger the target to continue into the measurement too:
+	 */
+	atomic_inc(&start_count);
+
+	check_tsc_warp(loop_timeout(cpu));
+
+	while (atomic_read(&stop_count) != cpus-1)
+		cpu_relax();
+
+	/*
+	 * If the test was successful set the number of runs to zero and
+	 * stop. If not, decrement the number of runs an check if we can
+	 * retry. In case of random warps no retry is attempted.
+	 */
+	if (!nr_warps) {
+		atomic_set(&test_runs, 0);
+
+		pr_debug("TSC synchronization [CPU#%d -> CPU#%u]: passed\n",
+			smp_processor_id(), cpu);
+
+	} else if (atomic_dec_and_test(&test_runs) || random_warps) {
+		/* Force it to 0 if random warps brought us here */
+		atomic_set(&test_runs, 0);
+
+		pr_warn("TSC synchronization [CPU#%d -> CPU#%u]:\n",
+			smp_processor_id(), cpu);
+		pr_warn("Measured %Ld cycles TSC warp between CPUs, "
+			"turning off TSC clock.\n", max_warp);
+		if (random_warps)
+			pr_warn("TSC warped randomly between CPUs\n");
+		schedule_work(&tsc_sync_work);
+	}
+
+	/*
+	 * Reset it - just in case we boot another CPU later:
+	 */
+	atomic_set(&start_count, 0);
+	random_warps = 0;
+	nr_warps = 0;
+	max_warp = 0;
+	last_tsc = 0;
+
+	/*
+	 * Let the target continue with the bootup:
+	 */
+	atomic_inc(&stop_count);
+
+	/*
+	 * Retry, if there is a chance to do so.
+	 */
+	if (atomic_read(&test_runs) > 0)
+		goto retry;
+}
+
+/*
+ * Freshly booted CPUs call into this:
+ */
+void check_tsc_sync_target(void)
+{
+	struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust);
+	unsigned int cpu = smp_processor_id();
+	cycles_t cur_max_warp, gbl_max_warp;
+	int cpus = 2;
+
+	/* Also aborts if there is no TSC. */
+	if (unsynchronized_tsc())
+		return;
+
+	/*
+	 * Store, verify and sanitize the TSC adjust register. If
+	 * successful skip the test.
+	 *
+	 * The test is also skipped when the TSC is marked reliable. This
+	 * is true for SoCs which have no fallback clocksource. On these
+	 * SoCs the TSC is frequency synchronized, but still the TSC ADJUST
+	 * register might have been wreckaged by the BIOS..
+	 */
+	if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable)
+		return;
+
+	/* Kick the control CPU into the TSC synchronization function */
+	smp_call_function_single(cpumask_first(cpu_online_mask), check_tsc_sync_source,
+				 (unsigned long *)(unsigned long)cpu, 0);
+retry:
+	/*
+	 * Register this CPU's participation and wait for the
+	 * source CPU to start the measurement:
+	 */
+	atomic_inc(&start_count);
+	while (atomic_read(&start_count) != cpus)
+		cpu_relax();
+
+	cur_max_warp = check_tsc_warp(loop_timeout(cpu));
+
+	/*
+	 * Store the maximum observed warp value for a potential retry:
+	 */
+	gbl_max_warp = max_warp;
+
+	/*
+	 * Ok, we are done:
+	 */
+	atomic_inc(&stop_count);
+
+	/*
+	 * Wait for the source CPU to print stuff:
+	 */
+	while (atomic_read(&stop_count) != cpus)
+		cpu_relax();
+
+	/*
+	 * Reset it for the next sync test:
+	 */
+	atomic_set(&stop_count, 0);
+
+	/*
+	 * Check the number of remaining test runs. If not zero, the test
+	 * failed and a retry with adjusted TSC is possible. If zero the
+	 * test was either successful or failed terminally.
+	 */
+	if (!atomic_read(&test_runs))
+		return;
+
+	/*
+	 * If the warp value of this CPU is 0, then the other CPU
+	 * observed time going backwards so this TSC was ahead and
+	 * needs to move backwards.
+	 */
+	if (!cur_max_warp)
+		cur_max_warp = -gbl_max_warp;
+
+	/*
+	 * Add the result to the previous adjustment value.
+	 *
+	 * The adjustment value is slightly off by the overhead of the
+	 * sync mechanism (observed values are ~200 TSC cycles), but this
+	 * really depends on CPU, node distance and frequency. So
+	 * compensating for this is hard to get right. Experiments show
+	 * that the warp is not longer detectable when the observed warp
+	 * value is used. In the worst case the adjustment needs to go
+	 * through a 3rd run for fine tuning.
+	 */
+	cur->adjusted += cur_max_warp;
+
+	pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n",
+		cpu, cur_max_warp, cur->adjusted);
+
+	wrmsrl(MSR_IA32_TSC_ADJUST, cur->adjusted);
+	goto retry;
+
+}
+
+#endif /* CONFIG_SMP */