Index: sys/kern/subr_smr.c
===================================================================
--- sys/kern/subr_smr.c
+++ sys/kern/subr_smr.c
@@ -146,6 +146,14 @@
 static uma_zone_t smr_shared_zone;
 static uma_zone_t smr_zone;
 
+enum {
+	BOOT_COLD = 1,
+	BOOT_ZONE = 2,
+	BOOT_PCPU = 3,
+} booted = BOOT_COLD;
+
+static smr_shared_t smr_init_list;
+
 #ifndef INVARIANTS
 #define	SMR_SEQ_INIT	1		/* All valid sequence numbers are odd. */
 #define	SMR_SEQ_INCR	2
@@ -582,30 +590,51 @@
 	return (success);
 }
 
+static void
+smr_init_cpu(smr_shared_t s, int cpu, int limit, int flags)
+{
+	smr_t c;
+
+	c = zpcpu_get_cpu(s->s_cpu, cpu);
+	c->c_seq = SMR_SEQ_INVALID;
+	c->c_shared = s;
+	c->c_deferred = 0;
+	c->c_limit = limit;
+	c->c_flags = flags;
+}
+
 smr_t
 smr_create(const char *name, int limit, int flags)
 {
-	smr_t smr, c;
+	smr_t smr;
 	smr_shared_t s;
 	int i;
 
+	KASSERT(booted >= BOOT_ZONE,
+	    ("%s: SMR is not yet initialized", __func__));
+
 	s = uma_zalloc(smr_shared_zone, M_WAITOK);
 	smr = uma_zalloc_pcpu(smr_zone, M_WAITOK);
 
 	s->s_name = name;
 	s->s_rd_seq = s->s_wr.seq = SMR_SEQ_INIT;
 	s->s_wr.ticks = ticks;
+	s->s_cpu = smr;
 
-	/* Initialize all CPUS, not just those running. */
-	for (i = 0; i <= mp_maxid; i++) {
-		c = zpcpu_get_cpu(smr, i);
-		c->c_seq = SMR_SEQ_INVALID;
-		c->c_shared = s;
-		c->c_deferred = 0;
-		c->c_limit = limit;
-		c->c_flags = flags;
+	smr_init_cpu(s, 0, limit, flags);
+	if (booted < BOOT_PCPU) {
+		/*
+		 * Per-CPU memory for APs might not be accessible at this point.
+		 * Defer initialization of the rest of the CPU sections.
+		 */
+		s->s_next = smr_init_list;
+		smr_init_list = s;
+	} else {
+		/* Initialize all CPUs, not just those running. */
+		for (i = 1; i <= mp_maxid; i++)
+			smr_init_cpu(s, i, limit, flags);
+		atomic_thread_fence_seq_cst();
 	}
-	atomic_thread_fence_seq_cst();
 
 	return (smr);
 }
@@ -622,12 +651,33 @@
 /*
  * Initialize the UMA slab zone.
  */
-void
-smr_init(void)
+static void
+smr_init(void *arg __unused)
 {
 
 	smr_shared_zone = uma_zcreate("SMR SHARED", sizeof(struct smr_shared),
 	    NULL, NULL, NULL, NULL, (CACHE_LINE_SIZE * 2) - 1, 0);
 	smr_zone = uma_zcreate("SMR CPU", sizeof(struct smr),
 	    NULL, NULL, NULL, NULL, (CACHE_LINE_SIZE * 2) - 1, UMA_ZONE_PCPU);
+	booted = BOOT_ZONE;
+}
+SYSINIT(smr_init, SI_SUB_SMR, SI_ORDER_FIRST, smr_init, NULL);
+
+static void
+smr_init2(void *arg __unused)
+{
+	smr_shared_t s;
+	smr_t c0;
+	int i;
+
+	/*
+	 * Complete initialization of per-CPU sections, started in smr_create().
+	 */
+	for (s = smr_init_list; s != NULL; s = s->s_next) {
+		c0 = zpcpu_get_cpu(s->s_cpu, 0);
+		for (i = 1; i <= mp_maxid; i++)
+			smr_init_cpu(s, i, c0->c_limit, c0->c_flags);
+	}
+	booted = BOOT_PCPU;
 }
+SYSINIT(smr_init2, SI_SUB_CPU, SI_ORDER_ANY, smr_init2, NULL);
Index: sys/sys/kernel.h
===================================================================
--- sys/sys/kernel.h
+++ sys/sys/kernel.h
@@ -92,6 +92,7 @@
 	SI_SUB_TUNABLES		= 0x0700000,	/* establish tunable values */
 	SI_SUB_COPYRIGHT	= 0x0800001,	/* first use of console*/
 	SI_SUB_VM		= 0x1000000,	/* virtual memory system init */
+	SI_SUB_SMR		= 0x1010000,	/* SMR is initialized */
 	SI_SUB_COUNTER		= 0x1100000,	/* counter(9) is initialized */
 	SI_SUB_KMEM		= 0x1800000,	/* kernel memory*/
 	SI_SUB_HYPERVISOR	= 0x1A40000,	/*
Index: sys/sys/smr.h
===================================================================
--- sys/sys/smr.h
+++ sys/sys/smr.h
@@ -65,9 +65,11 @@
 	uint64_t	_pair;
 };
 struct smr_shared {
-	const char	*s_name;	/* Name for debugging/reporting. */
 	union s_wr	s_wr;		/* Write sequence */
 	smr_seq_t	s_rd_seq;	/* Minimum observed read sequence. */
+	smr_t		s_cpu;		/* Per-CPU sections. */
+	struct smr_shared *s_next;	/* Deferred init list entry. */
+	const char	*s_name;	/* Name for debugging/reporting. */
 };
 typedef struct smr_shared *smr_shared_t;
 
@@ -255,7 +257,4 @@
         smr_wait(smr, smr_advance(smr));
 }
 
-/* Only at startup. */
-void smr_init(void);
-
 #endif	/* _SYS_SMR_H_ */
Index: sys/vm/uma_core.c
===================================================================
--- sys/vm/uma_core.c
+++ sys/vm/uma_core.c
@@ -2228,6 +2228,9 @@
 		keg->uk_flags |= UMA_ZONE_ROUNDROBIN;
 #endif
 
+	KASSERT(booted >= BOOT_KVA || (keg->uk_flags & UMA_ZONE_PCPU) == 0,
+	    ("%s: early pcpu keg %s", __func__, keg->uk_name));
+
 	/*
 	 * If we haven't booted yet we need allocations to go through the
 	 * startup cache until the vm is ready.
@@ -2307,10 +2310,7 @@
 
 	if (keg->uk_allocf == startup_alloc) {
 		/* Switch to the real allocator. */
-		if (keg->uk_flags & UMA_ZONE_PCPU)
-			keg->uk_allocf = pcpu_page_alloc;
-		else if ((keg->uk_flags & UMA_ZONE_CONTIG) != 0 &&
-		    keg->uk_ppera > 1)
+		if ((keg->uk_flags & UMA_ZONE_CONTIG) != 0 && keg->uk_ppera > 1)
 			keg->uk_allocf = contig_alloc;
 		else
 			keg->uk_allocf = page_alloc;
@@ -2869,7 +2869,6 @@
 	    NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZFLAG_INTERNAL);
 
 	bucket_init();
-	smr_init();
 }
 
 #ifndef UMA_MD_SMALL_ALLOC
@@ -3312,7 +3311,7 @@
 #ifdef UMA_ZALLOC_DEBUG
 	void *item;
 
-	KASSERT((zone->uz_flags & UMA_ZONE_SMR) != 0,
+	KASSERT((zone->uz_flags & UMA_ZONE_SMR) != 0 || !smp_started,
 	    ("uma_zalloc_arg: called with non-SMR zone.\n"));
 	if (uma_zalloc_debug(zone, &item, NULL, flags) == EJUSTRETURN)
 		return (item);
@@ -4655,7 +4654,8 @@
 uma_zone_set_smr(uma_zone_t zone, smr_t smr)
 {
 
-	ZONE_ASSERT_COLD(zone);
+	if (smp_started)
+		ZONE_ASSERT_COLD(zone);
 
 	KASSERT(smr != NULL, ("Got NULL smr"));
 	KASSERT((zone->uz_flags & UMA_ZONE_SMR) == 0,
Index: sys/vm/vm_radix.c
===================================================================
--- sys/vm/vm_radix.c
+++ sys/vm/vm_radix.c
@@ -375,10 +375,20 @@
 
 	vm_radix_node_zone = uma_zcreate("RADIX NODE",
 	    sizeof(struct vm_radix_node), NULL, NULL, NULL, NULL,
-	    VM_RADIX_PAD, UMA_ZONE_VM | UMA_ZONE_SMR | UMA_ZONE_ZINIT);
-	vm_radix_smr = uma_zone_get_smr(vm_radix_node_zone);
+	    VM_RADIX_PAD, UMA_ZONE_VM | UMA_ZONE_ZINIT);
 }
 
+/*
+ * Attach SMR structures to the radix node zone.
+ */
+static void
+vm_radix_zinit2(void *arg __unused)
+{
+	vm_radix_smr = smr_create("RADIX NODE", 0, 0);
+	uma_zone_set_smr(vm_radix_node_zone, vm_radix_smr);
+}
+SYSINIT(vm_radix_zinit2, SI_SUB_SMR, SI_ORDER_ANY, vm_radix_zinit2, NULL);
+
 /*
  * Inserts the key-value pair into the trie.
  * Panics if the key already exists.