virtio_scsi: support multi hw queue of blk-mq

Since virtio_scsi has supported multi virtqueue already,
it is natural to map the virtque to hw-queue of blk-mq.
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/virtio_scsi.c

@@ -561,6 +561,15 @@ static int virtscsi_queuecommand_single(struct Scsi_Host *sh,
 	return virtscsi_queuecommand(vscsi, &vscsi->req_vqs[0], sc);
 }
 
+static struct virtio_scsi_vq *virtscsi_pick_vq_mq(struct virtio_scsi *vscsi,
+						  struct scsi_cmnd *sc)
+{
+	u32 tag = blk_mq_unique_tag(sc->request);
+	u16 hwq = blk_mq_unique_tag_to_hwq(tag);
+
+	return &vscsi->req_vqs[hwq];
+}
+
 static struct virtio_scsi_vq *virtscsi_pick_vq(struct virtio_scsi *vscsi,
 					       struct virtio_scsi_target_state *tgt)
 {
@@ -604,7 +613,12 @@ static int virtscsi_queuecommand_multi(struct Scsi_Host *sh,
 	struct virtio_scsi *vscsi = shost_priv(sh);
 	struct virtio_scsi_target_state *tgt =
 				scsi_target(sc->device)->hostdata;
-	struct virtio_scsi_vq *req_vq = virtscsi_pick_vq(vscsi, tgt);
+	struct virtio_scsi_vq *req_vq;
+
+	if (shost_use_blk_mq(sh))
+		req_vq = virtscsi_pick_vq_mq(vscsi, sc);
+	else
+		req_vq = virtscsi_pick_vq(vscsi, tgt);
 
 	return virtscsi_queuecommand(vscsi, req_vq, sc);
 }
@@ -981,6 +995,7 @@ static int virtscsi_probe(struct virtio_device *vdev)
 	shost->max_id = num_targets;
 	shost->max_channel = 0;
 	shost->max_cmd_len = VIRTIO_SCSI_CDB_SIZE;
+	shost->nr_hw_queues = num_queues;
 
 	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_T10_PI)) {
 		host_prot = SHOST_DIF_TYPE1_PROTECTION | SHOST_DIF_TYPE2_PROTECTION |