Index: head/sys/dev/hyperv/include/hyperv.h
===================================================================
--- head/sys/dev/hyperv/include/hyperv.h
+++ head/sys/dev/hyperv/include/hyperv.h
@@ -45,6 +45,7 @@
 #define CPUID_HV_MSR_HYPERCALL		0x0020	/* MSR_HV_GUEST_OS_ID
 						 * MSR_HV_HYPERCALL */
 #define CPUID_HV_MSR_VP_INDEX		0x0040	/* MSR_HV_VP_INDEX */
+#define CPUID_HV_MSR_REFERENCE_TSC	0x0200	/* MSR_HV_REFERENCE_TSC */
 #define CPUID_HV_MSR_GUEST_IDLE		0x0400	/* MSR_HV_GUEST_IDLE */
 
 #ifndef NANOSEC
Index: head/sys/dev/hyperv/vmbus/amd64/hyperv_machdep.c
===================================================================
--- head/sys/dev/hyperv/vmbus/amd64/hyperv_machdep.c
+++ head/sys/dev/hyperv/vmbus/amd64/hyperv_machdep.c
@@ -28,7 +28,37 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/systm.h>
+#include <sys/timetc.h>
+
+#include <machine/cpufunc.h>
+#include <machine/cputypes.h>
+#include <machine/md_var.h>
+
+#include <dev/hyperv/include/hyperv.h>
+#include <dev/hyperv/include/hyperv_busdma.h>
 #include <dev/hyperv/vmbus/hyperv_machdep.h>
+#include <dev/hyperv/vmbus/hyperv_reg.h>
+#include <dev/hyperv/vmbus/hyperv_var.h>
+
+struct hyperv_reftsc_ctx {
+	struct hyperv_reftsc	*tsc_ref;
+	struct hyperv_dma	tsc_ref_dma;
+};
+
+static struct timecounter	hyperv_tsc_timecounter = {
+	.tc_get_timecount	= NULL,	/* based on CPU vendor. */
+	.tc_poll_pps		= NULL,
+	.tc_counter_mask	= 0xffffffff,
+	.tc_frequency		= HYPERV_TIMER_FREQ,
+	.tc_name		= "Hyper-V-TSC",
+	.tc_quality		= 3000,
+	.tc_flags		= 0,
+	.tc_priv		= NULL
+};
+
+static struct hyperv_reftsc_ctx	hyperv_ref_tsc;
 
 uint64_t
 hypercall_md(volatile void *hc_addr, uint64_t in_val,
@@ -41,3 +71,85 @@
 	    "c" (in_val), "d" (in_paddr), "m" (hc_addr));
 	return (status);
 }
+
+#define HYPERV_TSC_TIMECOUNT(fence)					\
+static u_int								\
+hyperv_tsc_timecount_##fence(struct timecounter *tc)			\
+{									\
+	struct hyperv_reftsc *tsc_ref = hyperv_ref_tsc.tsc_ref;		\
+	uint32_t seq;							\
+									\
+	while ((seq = atomic_load_acq_int(&tsc_ref->tsc_seq)) != 0) {	\
+		uint64_t disc, ret, tsc;				\
+		uint64_t scale = tsc_ref->tsc_scale;			\
+		int64_t ofs = tsc_ref->tsc_ofs;				\
+									\
+		fence();						\
+		tsc = rdtsc();						\
+									\
+		/* ret = ((tsc * scale) >> 64) + ofs */			\
+		__asm__ __volatile__ ("mulq %3" :			\
+		    "=d" (ret), "=a" (disc) :				\
+		    "a" (tsc), "r" (scale));				\
+		ret += ofs;						\
+									\
+		atomic_thread_fence_acq();				\
+		if (tsc_ref->tsc_seq == seq)				\
+			return (ret);					\
+									\
+		/* Sequence changed; re-sync. */			\
+	}								\
+	/* Fallback to the generic timecounter, i.e. rdmsr. */		\
+	return (rdmsr(MSR_HV_TIME_REF_COUNT));				\
+}									\
+struct __hack
+
+HYPERV_TSC_TIMECOUNT(lfence);
+HYPERV_TSC_TIMECOUNT(mfence);
+
+static void
+hyperv_tsc_tcinit(void *dummy __unused)
+{
+	uint64_t val, orig;
+
+	if ((hyperv_features &
+	     (CPUID_HV_MSR_TIME_REFCNT | CPUID_HV_MSR_REFERENCE_TSC)) !=
+	    (CPUID_HV_MSR_TIME_REFCNT | CPUID_HV_MSR_REFERENCE_TSC) ||
+	    (cpu_feature & CPUID_SSE2) == 0)	/* SSE2 for mfence/lfence */
+		return;
+
+	switch (cpu_vendor_id) {
+	case CPU_VENDOR_AMD:
+		hyperv_tsc_timecounter.tc_get_timecount =
+		    hyperv_tsc_timecount_mfence;
+		break;
+
+	case CPU_VENDOR_INTEL:
+		hyperv_tsc_timecounter.tc_get_timecount =
+		    hyperv_tsc_timecount_lfence;
+		break;
+
+	default:
+		/* Unsupport CPU vendors. */
+		return;
+	}
+
+	hyperv_ref_tsc.tsc_ref = hyperv_dmamem_alloc(NULL, PAGE_SIZE, 0,
+	    sizeof(struct hyperv_reftsc), &hyperv_ref_tsc.tsc_ref_dma,
+	    BUS_DMA_WAITOK | BUS_DMA_ZERO);
+	if (hyperv_ref_tsc.tsc_ref == NULL) {
+		printf("hyperv: reftsc page allocation failed\n");
+		return;
+	}
+
+	orig = rdmsr(MSR_HV_REFERENCE_TSC);
+	val = MSR_HV_REFTSC_ENABLE | (orig & MSR_HV_REFTSC_RSVD_MASK) |
+	    ((hyperv_ref_tsc.tsc_ref_dma.hv_paddr >> PAGE_SHIFT) <<
+	     MSR_HV_REFTSC_PGSHIFT);
+	wrmsr(MSR_HV_REFERENCE_TSC, val);
+
+	/* Register "enlightened" timecounter. */
+	tc_init(&hyperv_tsc_timecounter);
+}
+SYSINIT(hyperv_tsc_init, SI_SUB_DRIVERS, SI_ORDER_FIRST, hyperv_tsc_tcinit,
+    NULL);
Index: head/sys/dev/hyperv/vmbus/hyperv_reg.h
===================================================================
--- head/sys/dev/hyperv/vmbus/hyperv_reg.h
+++ head/sys/dev/hyperv/vmbus/hyperv_reg.h
@@ -57,6 +57,11 @@
 
 #define MSR_HV_VP_INDEX			0x40000002
 
+#define MSR_HV_REFERENCE_TSC		0x40000021
+#define MSR_HV_REFTSC_ENABLE		0x0001ULL
+#define MSR_HV_REFTSC_RSVD_MASK		0x0ffeULL
+#define MSR_HV_REFTSC_PGSHIFT		12
+
 #define MSR_HV_SCONTROL			0x40000080
 #define MSR_HV_SCTRL_ENABLE		0x0001ULL
 #define MSR_HV_SCTRL_RSVD_MASK		0xfffffffffffffffeULL
@@ -124,6 +129,17 @@
 #define CPUID_LEAF_HV_HWFEATURES	0x40000006
 
 /*
+ * Hyper-V Reference TSC
+ */
+struct hyperv_reftsc {
+	volatile uint32_t	tsc_seq;
+	volatile uint32_t	tsc_rsvd1;
+	volatile uint64_t	tsc_scale;
+	volatile int64_t	tsc_ofs;
+} __packed __aligned(PAGE_SIZE);
+CTASSERT(sizeof(struct hyperv_reftsc) == PAGE_SIZE);
+
+/*
  * Hyper-V Monitor Notification Facility
  */
 struct hyperv_mon_param {