The current configuration sets the virtqueue (vq) to premapped mode,
implying that all buffers submitted to this queue must be mapped ahead
of time. This presents a challenge for the virtnet send queue (sq): the
virtnet driver would be required to keep track of dma information for vq
size * 17, which can be substantial. However, if the premapped mode were
applied on a per-buffer basis, the complexity would be greatly reduced.
With AF_XDP enabled, AF_XDP buffers would become premapped, while kernel
skb buffers could remain unmapped.
We can distinguish them by sg_page(sg), When sg_page(sg) is NULL, this
indicates that the driver has performed DMA mapping in advance, allowing
the Virtio core to directly utilize sg_dma_address(sg) without
conducting any internal DMA mapping. Additionally, DMA unmap operations
for this buffer will be bypassed.
Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 67 +++++++++++++++++++++---------------
1 file changed, 40 insertions(+), 27 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 7d5fed4ff4f8..b570acb35d97 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -243,6 +243,7 @@ static void vring_free(struct virtqueue *_vq);
*/
#define to_vvq(_vq) container_of_const(_vq, struct vring_virtqueue, vq)
+#define sg_is_premapped(sg) (!sg_page(sg))
static bool virtqueue_use_indirect(const struct vring_virtqueue *vq,
unsigned int total_sg)
@@ -300,9 +301,10 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
return false;
}
-static bool vring_need_unmap_buffer(const struct vring_virtqueue *vring)
+static bool vring_need_unmap_buffer(const struct vring_virtqueue *vring,
+ const struct vring_desc_extra *extra)
{
- return vring->use_dma_api && !vring->premapped;
+ return vring->use_dma_api && (extra->addr != DMA_MAPPING_ERROR);
}
size_t virtio_max_dma_size(const struct virtio_device *vdev)
@@ -374,7 +376,7 @@ 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) {
+ if (sg_is_premapped(sg)) {
*addr = sg_dma_address(sg);
return 0;
}
@@ -465,7 +467,7 @@ 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 (!vring_need_unmap_buffer(vq))
+ if (!vring_need_unmap_buffer(vq, extra))
goto out;
dma_unmap_page(vring_dma_dev(vq),
@@ -518,7 +520,7 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
dma_addr_t addr,
unsigned int len,
u16 flags,
- bool indirect)
+ bool indirect, bool premapped)
{
u16 next;
@@ -526,7 +528,7 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
desc[i].addr = cpu_to_virtio64(vq->vdev, addr);
desc[i].len = cpu_to_virtio32(vq->vdev, len);
- extra[i].addr = addr;
+ extra[i].addr = premapped ? DMA_MAPPING_ERROR : addr;
extra[i].len = len;
extra[i].flags = flags;
@@ -619,7 +621,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
*/
i = virtqueue_add_desc_split(_vq, desc, extra, i, addr, sg->length,
VRING_DESC_F_NEXT,
- indirect);
+ indirect, sg_is_premapped(sg));
}
}
for (; n < (out_sgs + in_sgs); n++) {
@@ -637,12 +639,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
sg->length,
VRING_DESC_F_NEXT |
VRING_DESC_F_WRITE,
- indirect);
+ indirect, sg_is_premapped(sg));
}
}
/* Last one doesn't continue. */
desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
- if (!indirect && vring_need_unmap_buffer(vq))
+ if (!indirect && vring_need_unmap_buffer(vq, &extra[prev]))
vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
~VRING_DESC_F_NEXT;
@@ -651,19 +653,15 @@ 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 (vq->premapped)
- goto free_indirect;
-
+ if (vring_mapping_error(vq, addr))
goto unmap_release;
- }
virtqueue_add_desc_split(_vq, vq->split.vring.desc,
vq->split.desc_extra,
head, addr,
total_sg * sizeof(struct vring_desc),
VRING_DESC_F_INDIRECT,
- false);
+ false, false);
}
/* We're using some buffers from the free list. */
@@ -720,7 +718,6 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
i = vring_unmap_one_split(vq, &extra[i]);
}
-free_indirect:
if (indirect)
kfree(desc);
@@ -802,7 +799,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
VRING_DESC_F_INDIRECT));
BUG_ON(len == 0 || len % sizeof(struct vring_desc));
- if (vring_need_unmap_buffer(vq)) {
+ if (vq->use_dma_api) {
for (j = 0; j < len / sizeof(struct vring_desc); j++)
vring_unmap_one_split(vq, &extra[j]);
}
@@ -1236,7 +1233,7 @@ static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
(flags & VRING_DESC_F_WRITE) ?
DMA_FROM_DEVICE : DMA_TO_DEVICE);
} else {
- if (!vring_need_unmap_buffer(vq))
+ if (!vring_need_unmap_buffer(vq, extra))
return;
dma_unmap_page(vring_dma_dev(vq),
@@ -1318,7 +1315,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
desc[i].len = cpu_to_le32(sg->length);
if (unlikely(vq->use_dma_api)) {
- extra[i].addr = addr;
+ extra[i].addr = sg_is_premapped(sg) ? DMA_MAPPING_ERROR : addr;
extra[i].len = sg->length;
extra[i].flags = n < out_sgs ? 0 : VRING_DESC_F_WRITE;
}
@@ -1331,12 +1328,8 @@ 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 (vq->premapped)
- goto free_desc;
-
+ if (vring_mapping_error(vq, addr))
goto unmap_release;
- }
vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
@@ -1394,7 +1387,6 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
for (i = 0; i < err_idx; i++)
vring_unmap_extra_packed(vq, &extra[i]);
-free_desc:
kfree(desc);
END_USE(vq);
@@ -1485,7 +1477,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
desc[i].id = cpu_to_le16(id);
if (unlikely(vq->use_dma_api)) {
- vq->packed.desc_extra[curr].addr = addr;
+ vq->packed.desc_extra[curr].addr = sg_is_premapped(sg) ?
+ DMA_MAPPING_ERROR : addr;
vq->packed.desc_extra[curr].len = sg->length;
vq->packed.desc_extra[curr].flags =
le16_to_cpu(flags);
@@ -1635,7 +1628,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
if (!extra)
return;
- if (vring_need_unmap_buffer(vq)) {
+ if (vq->use_dma_api) {
len = vq->packed.desc_extra[id].len;
for (i = 0; i < len / sizeof(struct vring_packed_desc);
i++)
@@ -2222,6 +2215,11 @@ static inline int virtqueue_add(struct virtqueue *_vq,
* @data: the token identifying the buffer.
* @gfp: how to do memory allocations (if necessary).
*
+ * When sg_page(sg) is NULL, this indicates that the driver has performed DMA
+ * mapping in advance, allowing the virtio core to directly utilize
+ * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally,
+ * DMA unmap operations for this buffer will be bypassed.
+ *
* Caller must ensure we don't call this with other virtqueue operations
* at the same time (except where noted).
*
@@ -2256,6 +2254,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
* @data: the token identifying the buffer.
* @gfp: how to do memory allocations (if necessary).
*
+ * When sg_page(sg) is NULL, this indicates that the driver has performed DMA
+ * mapping in advance, allowing the virtio core to directly utilize
+ * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally,
+ * DMA unmap operations for this buffer will be bypassed.
+ *
* Caller must ensure we don't call this with other virtqueue operations
* at the same time (except where noted).
*
@@ -2278,6 +2281,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
* @data: the token identifying the buffer.
* @gfp: how to do memory allocations (if necessary).
*
+ * When sg_page(sg) is NULL, this indicates that the driver has performed DMA
+ * mapping in advance, allowing the virtio core to directly utilize
+ * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally,
+ * DMA unmap operations for this buffer will be bypassed.
+ *
* Caller must ensure we don't call this with other virtqueue operations
* at the same time (except where noted).
*
@@ -2301,6 +2309,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
* @ctx: extra context for the token
* @gfp: how to do memory allocations (if necessary).
*
+ * When sg_page(sg) is NULL, this indicates that the driver has performed DMA
+ * mapping in advance, allowing the virtio core to directly utilize
+ * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally,
+ * DMA unmap operations for this buffer will be bypassed.
+ *
* Caller must ensure we don't call this with other virtqueue operations
* at the same time (except where noted).
*
--
2.32.0.3.g01195cf9f
