Index: head/sys/dev/nvme/nvme_qpair.c
===================================================================
--- head/sys/dev/nvme/nvme_qpair.c
+++ head/sys/dev/nvme/nvme_qpair.c
@@ -401,9 +401,13 @@
 		req->retries++;
 		nvme_qpair_submit_tracker(qpair, tr);
 	} else {
-		if (req->type != NVME_REQUEST_NULL)
+		if (req->type != NVME_REQUEST_NULL) {
+			bus_dmamap_sync(qpair->dma_tag_payload,
+			    tr->payload_dma_map,
+			    BUS_DMASYNC_POSTREAD | BUS_DMASYNC_POSTWRITE);
 			bus_dmamap_unload(qpair->dma_tag_payload,
 			    tr->payload_dma_map);
+		}
 
 		nvme_free_request(req);
 		tr->req = NULL;
@@ -487,6 +491,8 @@
 		 */
 		return (false);
 
+	bus_dmamap_sync(qpair->dma_tag, qpair->queuemem_map,
+	    BUS_DMASYNC_POSTREAD | BUS_DMASYNC_POSTWRITE);
 	while (1) {
 		cpl = qpair->cpl[qpair->cq_head];
 
@@ -828,7 +834,16 @@
 	if (++qpair->sq_tail == qpair->num_entries)
 		qpair->sq_tail = 0;
 
+	bus_dmamap_sync(qpair->dma_tag, qpair->queuemem_map,
+	    BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
+#ifndef __powerpc__
+	/*
+	 * powerpc's bus_dmamap_sync() already includes a heavyweight sync, but
+	 * no other archs do.
+	 */
 	wmb();
+#endif
+
 	nvme_mmio_write_4(qpair->ctrlr, doorbell[qpair->id].sq_tdbl,
 	    qpair->sq_tail);
 
@@ -879,6 +894,8 @@
 		tr->req->cmd.prp2 = 0;
 	}
 
+	bus_dmamap_sync(tr->qpair->dma_tag_payload, tr->payload_dma_map,
+	    BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
 	nvme_qpair_submit_tracker(tr->qpair, tr);
 }