Index: lib/libvmmapi/vmmapi.h
===================================================================
--- lib/libvmmapi/vmmapi.h
+++ lib/libvmmapi/vmmapi.h
@@ -211,6 +211,10 @@
 int	vm_suspended_cpus(struct vmctx *ctx, cpuset_t *cpus);
 int	vm_activate_cpu(struct vmctx *ctx, int vcpu);
 
+/* Set cpu topology */
+int	vm_set_topology(struct vmctx *ctx, uint64_t sockets, uint64_t cores, \
+	    uint64_t threads, uint64_t maxcpus);
+
 /*
  * FreeBSD specific APIs
  */
Index: lib/libvmmapi/vmmapi.c
===================================================================
--- lib/libvmmapi/vmmapi.c
+++ lib/libvmmapi/vmmapi.c
@@ -1420,6 +1420,20 @@
 }
 
 int
+vm_set_topology(struct vmctx *ctx, \
+    uint64_t sockets, uint64_t cores, uint64_t threads, uint64_t maxcpus)
+{
+	struct vm_cpu_topology topology;
+
+	bzero(&topology, sizeof (struct vm_cpu_topology));
+	topology.sockets = sockets;
+	topology.cores = cores;
+	topology.threads = threads;
+	topology.maxcpus = maxcpus;
+	return (ioctl(ctx->fd, VM_SET_TOPOLOGY, &topology));
+}
+
+int
 vm_get_device_fd(struct vmctx *ctx)
 {
 
@@ -1446,7 +1460,7 @@
 	    VM_GET_HPET_CAPABILITIES, VM_GET_GPA_PMAP, VM_GLA2GPA,
 	    VM_ACTIVATE_CPU, VM_GET_CPUS, VM_SET_INTINFO, VM_GET_INTINFO,
 	    VM_RTC_WRITE, VM_RTC_READ, VM_RTC_SETTIME, VM_RTC_GETTIME,
-	    VM_RESTART_INSTRUCTION };
+	    VM_RESTART_INSTRUCTION, VM_SET_TOPOLOGY, VM_GET_TOPOLOGY };
 
 	if (len == NULL) {
 		cmds = malloc(sizeof(vm_ioctl_cmds));
Index: sys/amd64/include/vmm.h
===================================================================
--- sys/amd64/include/vmm.h
+++ sys/amd64/include/vmm.h
@@ -181,6 +181,10 @@
 void vm_destroy(struct vm *vm);
 int vm_reinit(struct vm *vm);
 const char *vm_name(struct vm *vm);
+void vm_get_topology(struct vm *vm, uint64_t *sockets, uint64_t *cores,
+    uint64_t *threads, uint64_t *maxcpus);
+int vm_set_topology(struct vm *vm, uint64_t sockets, uint64_t cores,
+    uint64_t threads, uint64_t maxcpus);
 
 /*
  * APIs that modify the guest memory map require all vcpus to be frozen.
Index: sys/amd64/include/vmm_dev.h
===================================================================
--- sys/amd64/include/vmm_dev.h
+++ sys/amd64/include/vmm_dev.h
@@ -218,6 +218,13 @@
 	uint8_t		value;
 };
 
+struct vm_cpu_topology {
+	uint64_t	sockets;
+	uint64_t	cores;
+	uint64_t	threads;
+	uint64_t	maxcpus;
+};
+
 enum {
 	/* general routines */
 	IOCNUM_ABIVERS = 0,
@@ -273,6 +280,10 @@
 	IOCNUM_GET_X2APIC_STATE = 61,
 	IOCNUM_GET_HPET_CAPABILITIES = 62,
 
+	/* CPU Topology */
+	IOCNUM_SET_TOPOLOGY = 63,
+	IOCNUM_GET_TOPOLOGY = 64,
+
 	/* legacy interrupt injection */
 	IOCNUM_ISA_ASSERT_IRQ = 80,
 	IOCNUM_ISA_DEASSERT_IRQ = 81,
@@ -384,4 +395,8 @@
 	_IOR('v', IOCNUM_RTC_GETTIME, struct vm_rtc_time)
 #define	VM_RESTART_INSTRUCTION \
 	_IOW('v', IOCNUM_RESTART_INSTRUCTION, int)
+#define VM_SET_TOPOLOGY \
+	_IOW('v', IOCNUM_SET_TOPOLOGY, struct vm_cpu_topology)
+#define VM_GET_TOPOLOGY \
+	_IOR('v', IOCNUM_GET_TOPOLOGY, struct vm_cpu_topology)
 #endif
Index: sys/amd64/vmm/vmm.c
===================================================================
--- sys/amd64/vmm/vmm.c
+++ sys/amd64/vmm/vmm.c
@@ -165,6 +165,11 @@
 	struct vmspace	*vmspace;		/* (o) guest's address space */
 	char		name[VM_MAX_NAMELEN];	/* (o) virtual machine name */
 	struct vcpu	vcpu[VM_MAXCPU];	/* (i) guest vcpus */
+	/* The following describe the vm cpu topology */
+	uint64_t	sockets;		/* (o) num of sockets */
+	uint64_t	cores;			/* (o) num of cores/socket */
+	uint64_t	threads;		/* (o) num of threads/core */
+	uint64_t	maxcpus;		/* (o) max pluggable cpus */
 };
 
 static int vmm_initialized;
@@ -423,6 +428,9 @@
 		vcpu_init(vm, i, create);
 }
 
+extern u_int cores_per_package;
+extern u_int threads_per_core;
+
 int
 vm_create(const char *name, struct vm **retvm)
 {
@@ -448,6 +456,11 @@
 	vm->vmspace = vmspace;
 	mtx_init(&vm->rendezvous_mtx, "vm rendezvous lock", 0, MTX_DEF);
 
+	vm->sockets=1;
+	vm->cores=cores_per_package;	/* XXX backwards compatibility */
+	vm->threads=threads_per_core;	/* XXX backwards compatibility */
+	vm->maxcpus=0;			/* XXX not implemented */
+
 	vm_init(vm, true);
 
 	*retvm = vm;
@@ -454,6 +467,30 @@
 	return (0);
 }
 
+void
+vm_get_topology(struct vm *vm, uint64_t *sockets, uint64_t *cores,
+    uint64_t *threads, uint64_t *maxcpus)
+{
+	*sockets = vm->sockets;
+	*cores = vm->cores;
+	*threads = vm->threads;
+	*maxcpus = vm->maxcpus;
+}
+
+int
+vm_set_topology(struct vm *vm, uint64_t sockets, uint64_t cores,
+    uint64_t threads, uint64_t maxcpus)
+{
+	if (maxcpus != 0) return (EINVAL);	/* XXX remove when supported */
+	if ((sockets * cores * threads) > VM_MAXCPU) return (EINVAL);
+	/* XXX need to check sockets * cores * threads == vCPU, how? */
+	vm->sockets = sockets;
+	vm->cores = cores;
+	vm->threads = threads;
+	vm->maxcpus = maxcpus;
+	return(0);
+}
+
 static void
 vm_cleanup(struct vm *vm, bool destroy)
 {
Index: sys/amd64/vmm/vmm_dev.c
===================================================================
--- sys/amd64/vmm/vmm_dev.c
+++ sys/amd64/vmm/vmm_dev.c
@@ -315,6 +315,7 @@
 	struct vm_rtc_time *rtctime;
 	struct vm_rtc_data *rtcdata;
 	struct vm_memmap *mm;
+	struct vm_cpu_topology *topology;
 
 	sc = vmmdev_lookup2(cdev);
 	if (sc == NULL)
@@ -642,6 +643,14 @@
 	case VM_RESTART_INSTRUCTION:
 		error = vm_restart_instruction(sc->vm, vcpu);
 		break;
+	case VM_SET_TOPOLOGY:
+		topology = (struct vm_cpu_topology *)data;
+		error = vm_set_topology(sc->vm, topology->sockets,
+		    topology->cores, topology->threads, topology->maxcpus);
+		break;
+	case VM_GET_TOPOLOGY:
+		break;
+
 	default:
 		error = ENOTTY;
 		break;
Index: sys/amd64/vmm/x86.c
===================================================================
--- sys/amd64/vmm/x86.c
+++ sys/amd64/vmm/x86.c
@@ -63,12 +63,12 @@
 /*
  * The default CPU topology is a single thread per package.
  */
-static u_int threads_per_core = 1;
-SYSCTL_UINT(_hw_vmm_topology, OID_AUTO, threads_per_core, CTLFLAG_RDTUN,
+u_int threads_per_core = 1;
+SYSCTL_UINT(_hw_vmm_topology, OID_AUTO, threads_per_core, CTLFLAG_RW,
     &threads_per_core, 0, NULL);
 
-static u_int cores_per_package = 1;
-SYSCTL_UINT(_hw_vmm_topology, OID_AUTO, cores_per_package, CTLFLAG_RDTUN,
+u_int cores_per_package = 1;
+SYSCTL_UINT(_hw_vmm_topology, OID_AUTO, cores_per_package, CTLFLAG_RW,
     &cores_per_package, 0, NULL);
 
 static int cpuid_leaf_b = 1;
@@ -91,7 +91,7 @@
 		  uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
 {
 	const struct xsave_limits *limits;
-	uint64_t cr4;
+	uint64_t cores, cr4, maxcpus, sockets, threads;
 	int error, enable_invpcid, level, width, x2apic_id;
 	unsigned int func, regs[4], logical_cpus;
 	enum x2apic_state x2apic_state;
@@ -142,11 +142,12 @@
 				 *
 				 * However this matches the logical cpus as
 				 * advertised by leaf 0x1 and will work even
-				 * if the 'threads_per_core' tunable is set
-				 * incorrectly on an AMD host.
+				 * if threads is set incorrectly on an AMD host.
 				 */
-				logical_cpus = threads_per_core *
-				    cores_per_package;
+				vm_get_topology(vm, &sockets, &cores, &threads,
+				    &maxcpus);
+				logical_cpus = threads *
+				    cores;
 				regs[2] = logical_cpus - 1;
 			}
 			break;
@@ -305,7 +306,9 @@
 			 */
 			regs[3] |= (CPUID_MCA | CPUID_MCE | CPUID_MTRR);
 
-			logical_cpus = threads_per_core * cores_per_package;
+			vm_get_topology(vm, &sockets, &cores, &threads,
+			    &maxcpus);
+			logical_cpus = threads * cores;
 			regs[1] &= ~CPUID_HTT_CORES;
 			regs[1] |= (logical_cpus & 0xff) << 16;
 			regs[3] |= CPUID_HTT;
@@ -315,8 +318,10 @@
 			cpuid_count(*eax, *ecx, regs);
 
 			if (regs[0] || regs[1] || regs[2] || regs[3]) {
+				vm_get_topology(vm, &sockets, &cores, &threads,
+				    &maxcpus);
 				regs[0] &= 0x3ff;
-				regs[0] |= (cores_per_package - 1) << 26;
+				regs[0] |= (cores - 1) << 26;
 				/*
 				 * Cache topology:
 				 * - L1 and L2 are shared only by the logical
@@ -324,10 +329,10 @@
 				 * - L3 and above are shared by all logical
 				 *   processors in the package.
 				 */
-				logical_cpus = threads_per_core;
+				logical_cpus = threads;
 				level = (regs[0] >> 5) & 0x7;
 				if (level >= 3)
-					logical_cpus *= cores_per_package;
+					logical_cpus *= cores;
 				regs[0] |= (logical_cpus - 1) << 14;
 			}
 			break;
@@ -390,7 +395,9 @@
 			 * Processor topology enumeration
 			 */
 			if (*ecx == 0) {
-				logical_cpus = threads_per_core;
+				vm_get_topology(vm, &sockets, &cores, &threads,
+				    &maxcpus);
+				logical_cpus = threads;
 				width = log2(logical_cpus);
 				level = CPUID_TYPE_SMT;
 				x2apic_id = vcpu_id;
@@ -397,8 +404,8 @@
 			}
 
 			if (*ecx == 1) {
-				logical_cpus = threads_per_core *
-				    cores_per_package;
+				logical_cpus = threads *
+				    cores;
 				width = log2(logical_cpus);
 				level = CPUID_TYPE_CORE;
 				x2apic_id = vcpu_id;
Index: usr.sbin/bhyve/bhyve.8
===================================================================
--- usr.sbin/bhyve/bhyve.8
+++ usr.sbin/bhyve/bhyve.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 2, 2017
+.Dd February 17, 2018
 .Dt BHYVE 8
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl abehuwxACHPSWY
-.Op Fl c Ar numcpus
+.Op Fl c Oo Ar cpus= Oc Ns Ar numcpus Ns Oo Ar ,sockets=n Oc Ns Oo Ar ,cores=n Oc Ns Op Ar ,threads=n
 .Op Fl g Ar gdbport
 .Op Fl l Ar lpcdev Ns Op , Ns Ar conf
 .Op Fl m Ar memsize Ns Op Ar K|k|M|m|G|g|T|t
@@ -77,9 +77,28 @@
 kernels compiled with
 .Cd "device bvmconsole" .
 This option will be deprecated in a future version.
-.It Fl c Ar numcpus
-Number of guest virtual CPUs.
-The default is 1 and the maximum is 16.
+.It Fl c Oo Ar cpus= Oc Ns Ar numcpus Ns Oo Ar ,sockets=n Oc Ns Oo Ar ,cores=n Oc Ns Op Ar ,threads=n
+Number of guest virtual CPUs
+and optionally the CPU topology.
+The optional topology must be consistent in that the
+.Ar numcpus
+must equal the product of
+.Ar sockets
+*
+.Ar cores
+*
+.Ar threads .
+The default is 1 CPU
+implemented as 1 each of
+.Ar sockets ,
+.Ar cores ,
+and
+.Ar threads .
+If no topology is specified it is implemented as if
+.Ar sockets
+= 
+.Ar numcpus .
+There is a maximum of 16 virtual CPUs.
 .It Fl C
 Include guest memory in core file.
 .It Fl e
Index: usr.sbin/bhyve/bhyverun.c
===================================================================
--- usr.sbin/bhyve/bhyverun.c
+++ usr.sbin/bhyve/bhyverun.c
@@ -93,6 +93,11 @@
 char *vmname;
 
 int guest_ncpus;
+uint64_t sockets;
+uint64_t cores;
+uint64_t threads;
+uint64_t maxcpus;
+
 char *guest_uuid_str;
 
 static int guest_vmexit_on_hlt, guest_vmexit_on_pause;
@@ -165,6 +170,50 @@
 }
 
 static int
+topology_parse(const char *opt)
+{
+	char *cp, *str;
+	int i, tmp;
+
+	str = strdup(opt);
+	if ((cp = strchr(str, ',')) != NULL) {
+		for (i = 0; str; i++) {
+			if (sscanf(str, "cpus=%d", &tmp) == 1)
+				guest_ncpus = tmp;
+			else if (sscanf(str, "sockets=%d", &tmp) == 1)
+				sockets = tmp;
+			else if (sscanf(str, "cores=%d", &tmp) == 1)
+				cores = tmp;
+			else if (sscanf(str, "threads=%d", &tmp) == 1)
+				threads = tmp;
+#ifdef notyet  /* Do not expose this until vmm.ko implements it */
+			else if (sscanf(str, "maxcpus=%d", &tmp) == 1)
+				maxcpus = tmp;
+#endif
+			else
+				return (-1);
+			if (cp == NULL)
+				str = NULL;
+			else {
+				str = ++cp;
+				cp = strchr(str, ',');
+			}
+		}
+	} else {
+		if (sscanf(str, "cpus=%d", &tmp) == 1)
+			guest_ncpus = tmp;
+		else if (sscanf(str, "%d", &tmp) == 1)
+			guest_ncpus = tmp;
+		else
+			return (-1);
+	}
+	if (guest_ncpus != sockets * cores * threads)
+		return (-1);
+	else
+		return(0);
+}
+
+static int
 pincpu_parse(const char *opt)
 {
 	int vcpu, pcpu;
@@ -783,6 +832,11 @@
 			exit(1);
 		}
 	}
+	error = vm_set_topology(ctx, sockets, cores, threads, maxcpus);
+	if (error) {
+		perror("vm_set_topology");
+		exit(1);
+	}
 	return (ctx);
 }
 
@@ -801,6 +855,8 @@
 	progname = basename(argv[0]);
 	gdb_port = 0;
 	guest_ncpus = 1;
+	sockets = cores = threads = 1;
+	maxcpus = 0;
 	memsize = 256 * MB;
 	mptgen = 1;
 	rtc_localtime = 1;
@@ -825,7 +881,10 @@
                         }
 			break;
                 case 'c':
-			guest_ncpus = atoi(optarg);
+			if (topology_parse(optarg) !=0) {
+			    errx(EX_USAGE, "invalid cpu topology "
+				"'%s'", optarg);
+			}
 			break;
 		case 'C':
 			memflags |= VM_MEM_F_INCORE;