Index: head/sys/dev/sfxge/common/efx.h
===================================================================
--- head/sys/dev/sfxge/common/efx.h
+++ head/sys/dev/sfxge/common/efx.h
@@ -589,7 +589,6 @@
 	((_mask)[(_stat) / EFX_MAC_STATS_MASK_BITS_PER_PAGE] &	\
 	    (1ULL << ((_stat) & (EFX_MAC_STATS_MASK_BITS_PER_PAGE - 1))))
 
-#define	EFX_MAC_STATS_SIZE 0x400
 
 extern	__checkReturn			efx_rc_t
 efx_mac_stats_clear(
@@ -598,8 +597,8 @@
 /*
  * Upload mac statistics supported by the hardware into the given buffer.
  *
- * The reference buffer must be at least %EFX_MAC_STATS_SIZE bytes,
- * and page aligned.
+ * The DMA buffer must be 4Kbyte aligned and sized to hold at least
+ * efx_nic_cfg_t::enc_mac_stats_nstats 64bit counters.
  *
  * The hardware will only DMA statistics that it understands (of course).
  * Drivers should not make any assumptions about which statistics are
Index: head/sys/dev/sfxge/common/siena_mac.c
===================================================================
--- head/sys/dev/sfxge/common/siena_mac.c
+++ head/sys/dev/sfxge/common/siena_mac.c
@@ -463,7 +463,7 @@
 	SIENA_MAC_STAT_READ(esmp, MC_CMD_MAC_RX_NODESC_DROPS, &value);
 	EFSYS_STAT_SET_QWORD(&(stat[EFX_MAC_RX_NODESC_DROP_CNT]), &value);
 
-	EFSYS_DMA_SYNC_FOR_KERNEL(esmp, 0, EFX_MAC_STATS_SIZE);
+	EFSYS_DMA_SYNC_FOR_KERNEL(esmp, 0, EFSYS_MEM_SIZE(esmp));
 	EFSYS_MEM_READ_BARRIER();
 	SIENA_MAC_STAT_READ(esmp, MC_CMD_MAC_GENERATION_START,
 			    &generation_start);
Index: head/sys/dev/sfxge/sfxge_port.c
===================================================================
--- head/sys/dev/sfxge/sfxge_port.c
+++ head/sys/dev/sfxge/sfxge_port.c
@@ -753,6 +753,8 @@
 	struct sysctl_ctx_list *sysctl_ctx;
 	struct sysctl_oid *sysctl_tree;
 	efsys_mem_t *mac_stats_buf, *phy_stats_buf;
+	uint32_t mac_nstats;
+	size_t mac_stats_size;
 	int rc;
 
 	port = &sc->port;
@@ -792,7 +794,9 @@
 	DBGPRINT(sc->dev, "alloc MAC stats");
 	port->mac_stats.decode_buf = malloc(EFX_MAC_NSTATS * sizeof(uint64_t),
 					    M_SFXGE, M_WAITOK | M_ZERO);
-	if ((rc = sfxge_dma_alloc(sc, EFX_MAC_STATS_SIZE, mac_stats_buf)) != 0)
+	mac_nstats = efx_nic_cfg_get(sc->enp)->enc_mac_stats_nstats;
+	mac_stats_size = P2ROUNDUP(mac_nstats * sizeof(uint64_t), EFX_BUF_SIZE);
+	if ((rc = sfxge_dma_alloc(sc, mac_stats_size, mac_stats_buf)) != 0)
 		goto fail2;
 	port->stats_update_period_ms = sfxge_port_stats_update_period_ms(sc);
 	sfxge_mac_stat_init(sc);