[PATCH 4/6] virtio: split: virtqueue_add_split() support dma address

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

virtqueue_add_split() only supports virtual addresses, dma is completed
in virtqueue_add_split().

In some scenarios (such as the AF_XDP scenario), the memory is allocated
and DMA is completed in advance, so it is necessary for us to support
passing the DMA address to virtqueue_add_split().

This patch stipulates that if sg->dma_address is not NULL, use this
address as the DMA address. And record this information in extra->flags,
which can be skipped when executing dma unmap.

    extra->flags |= VRING_DESC_F_PREDMA;

This relies on the previous patch, in the indirect scenario, for each
desc allocated, an extra is allocated at the same time.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 7420741cb750..add8430d9678 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -66,6 +66,9 @@
 #define LAST_ADD_TIME_INVALID(vq)
 #endif
 
+/* This means the buffer dma is pre-alloc. Just used by vring_desc_extra */
+#define VRING_DESC_F_PREDMA	(1 << 15)
+
 struct vring_desc_extra {
 	dma_addr_t addr;		/* Descriptor DMA addr. */
 	u32 len;			/* Descriptor length. */
@@ -336,11 +339,19 @@ static inline struct device *vring_dma_dev(const struct vring_virtqueue *vq)
 	return vq->vq.vdev->dev.parent;
 }
 
+static inline bool sg_is_predma(struct scatterlist *sg)
+{
+	return !!sg->dma_address;
+}
+
 /* Map one sg entry. */
 static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
 				   struct scatterlist *sg,
 				   enum dma_data_direction direction)
 {
+	if (sg_is_predma(sg))
+		return sg_dma_address(sg);
+
 	if (!vq->use_dma_api)
 		return (dma_addr_t)sg_phys(sg);
 
@@ -396,6 +407,9 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
+		if (flags & VRING_DESC_F_PREDMA)
+			goto out;
+
 		dma_unmap_page(vring_dma_dev(vq),
 			       extra->addr,
 			       extra->len,
@@ -441,7 +455,8 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
 						    unsigned int i,
 						    dma_addr_t addr,
 						    unsigned int len,
-						    u16 flags)
+						    u16 flags,
+						    bool predma)
 {
 	struct vring_virtqueue *vring = to_vvq(vq);
 	struct vring_desc_extra *extra;
@@ -468,6 +483,9 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
 	extra->len = len;
 	extra->flags = flags;
 
+	if (predma)
+		extra->flags |= VRING_DESC_F_PREDMA;
+
 	return next;
 }
 
@@ -547,7 +565,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 			 * table since it use stream DMA mapping.
 			 */
 			i = virtqueue_add_desc_split(_vq, in, i, addr, sg->length,
-						     VRING_DESC_F_NEXT);
+						     VRING_DESC_F_NEXT,
+						     sg_is_predma(sg));
 		}
 	}
 	for (; n < (out_sgs + in_sgs); n++) {
@@ -563,7 +582,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 			i = virtqueue_add_desc_split(_vq, in, i, addr,
 						     sg->length,
 						     VRING_DESC_F_NEXT |
-						     VRING_DESC_F_WRITE);
+						     VRING_DESC_F_WRITE,
+						     sg_is_predma(sg));
 		}
 	}
 	/* Last one doesn't continue. */
@@ -582,7 +602,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 
 		virtqueue_add_desc_split(_vq, NULL, head, addr,
 					 total_sg * sizeof(struct vring_desc),
-					 VRING_DESC_F_INDIRECT);
+					 VRING_DESC_F_INDIRECT, false);
 	}
 
 	/* We're using some buffers from the free list. */
-- 
2.31.0

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