virtio_ring: support add premapped buf

If the vq is the premapped mode, use the sg_dma_address() directly.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Message-Id: <20230810123057.43407-5-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -361,6 +361,11 @@ static struct device *vring_dma_dev(const struct vring_virtqueue *vq)
 static int vring_map_one_sg(const struct vring_virtqueue *vq, struct scatterlist *sg,
 			    enum dma_data_direction direction, dma_addr_t *addr)
 {
+	if (vq->premapped) {
+		*addr = sg_dma_address(sg);
+		return 0;
+	}
+
 	if (!vq->use_dma_api) {
 		/*
 		 * If DMA is not used, KMSAN doesn't know that the scatterlist
@@ -639,8 +644,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		dma_addr_t addr = vring_map_single(
 			vq, desc, total_sg * sizeof(struct vring_desc),
 			DMA_TO_DEVICE);
-		if (vring_mapping_error(vq, addr))
+		if (vring_mapping_error(vq, addr)) {
+			if (vq->premapped)
+				goto free_indirect;
+
 			goto unmap_release;
+		}
 
 		virtqueue_add_desc_split(_vq, vq->split.vring.desc,
 					 head, addr,
@@ -706,6 +715,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 			i = vring_unmap_one_split(vq, i);
 	}
 
+free_indirect:
 	if (indirect)
 		kfree(desc);
 
@@ -1307,8 +1317,12 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	addr = vring_map_single(vq, desc,
 			total_sg * sizeof(struct vring_packed_desc),
 			DMA_TO_DEVICE);
-	if (vring_mapping_error(vq, addr))
+	if (vring_mapping_error(vq, addr)) {
+		if (vq->premapped)
+			goto free_desc;
+
 		goto unmap_release;
+	}
 
 	vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
 	vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
@@ -1366,6 +1380,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	for (i = 0; i < err_idx; i++)
 		vring_unmap_desc_packed(vq, &desc[i]);
 
+free_desc:
 	kfree(desc);
 
 	END_USE(vq);