Re: [PATCH vhost 03/17] virtio_ring: packed: structure the indirect desc table

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On Tue, Jan 30, 2024 at 7:42 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> This commit structure the indirect desc table.
> Then we can get the desc num directly when doing unmap.
>
> And save the dma info to the struct, then the indirect
> will not use the dma fields of the desc_extra. The subsequent
> commits will make the dma fields are optional. But for
> the indirect case, we must record the dma info.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/virtio/virtio_ring.c | 63 ++++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 7280a1706cca..dd03bc5a81fe 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -72,9 +72,16 @@ struct vring_desc_state_split {
>         struct vring_desc *indir_desc;  /* Indirect descriptor, if any. */
>  };
>
> +struct vring_packed_desc_indir {
> +       dma_addr_t addr;                /* Descriptor Array DMA addr. */
> +       u32 len;                        /* Descriptor Array length. */
> +       u32 num;
> +       struct vring_packed_desc desc[];
> +};
> +
>  struct vring_desc_state_packed {
>         void *data;                     /* Data for callback. */
> -       struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> +       struct vring_packed_desc_indir *indir_desc; /* Indirect descriptor, if any. */
>         u16 num;                        /* Descriptor list length. */
>         u16 last;                       /* The last desc state in a list. */
>  };
> @@ -1249,10 +1256,13 @@ static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
>                        DMA_FROM_DEVICE : DMA_TO_DEVICE);
>  }
>
> -static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
> +static struct vring_packed_desc_indir *alloc_indirect_packed(unsigned int total_sg,
>                                                        gfp_t gfp)
>  {
> -       struct vring_packed_desc *desc;
> +       struct vring_packed_desc_indir *in_desc;
> +       u32 size;
> +
> +       size = struct_size(in_desc, desc, total_sg);
>
>         /*
>          * We require lowmem mappings for the descriptors because
> @@ -1261,9 +1271,10 @@ static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
>          */
>         gfp &= ~__GFP_HIGHMEM;
>
> -       desc = kmalloc_array(total_sg, sizeof(struct vring_packed_desc), gfp);
>
> -       return desc;
> +       in_desc = kmalloc(size, gfp);
> +
> +       return in_desc;
>  }
>
>  static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> @@ -1274,6 +1285,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>                                          void *data,
>                                          gfp_t gfp)
>  {
> +       struct vring_packed_desc_indir *in_desc;
>         struct vring_packed_desc *desc;
>         struct scatterlist *sg;
>         unsigned int i, n, err_idx;
> @@ -1281,10 +1293,12 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>         dma_addr_t addr;
>
>         head = vq->packed.next_avail_idx;
> -       desc = alloc_indirect_packed(total_sg, gfp);
> -       if (!desc)
> +       in_desc = alloc_indirect_packed(total_sg, gfp);
> +       if (!in_desc)
>                 return -ENOMEM;
>
> +       desc = in_desc->desc;
> +
>         if (unlikely(vq->vq.num_free < 1)) {
>                 pr_debug("Can't add buf len 1 - avail = 0\n");
>                 kfree(desc);
> @@ -1321,17 +1335,15 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>                 goto unmap_release;
>         }
>
> +       in_desc->num = i;
> +       in_desc->addr = addr;
> +       in_desc->len = total_sg * sizeof(struct vring_packed_desc);

It looks to me if we don't use dma_api we don't even need these steps?

> +
>         vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
>         vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
>                                 sizeof(struct vring_packed_desc));
>         vq->packed.vring.desc[head].id = cpu_to_le16(id);
>
> -       if (vring_need_unmap_buffer(vq)) {
> -               vq->packed.desc_extra[id].addr = addr;
> -               vq->packed.desc_extra[id].len = total_sg *
> -                               sizeof(struct vring_packed_desc);
> -       }
> -
>         vq->packed.desc_extra[id].flags = VRING_DESC_F_INDIRECT |
>                 vq->packed.avail_used_flags;
>
> @@ -1362,7 +1374,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>         /* Store token and indirect buffer state. */
>         vq->packed.desc_state[id].num = 1;
>         vq->packed.desc_state[id].data = data;
> -       vq->packed.desc_state[id].indir_desc = desc;
> +       vq->packed.desc_state[id].indir_desc = in_desc;
>         vq->packed.desc_state[id].last = id;
>
>         vq->num_added += 1;
> @@ -1381,7 +1393,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>                 vring_unmap_desc_packed(vq, &desc[i]);
>
>  free_desc:
> -       kfree(desc);
> +       kfree(in_desc);
>
>         END_USE(vq);
>         return -ENOMEM;
> @@ -1595,7 +1607,6 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
>                               unsigned int id, void **ctx)
>  {
>         struct vring_desc_state_packed *state = NULL;
> -       struct vring_packed_desc *desc;
>         unsigned int i, curr;
>         u16 flags;
>
> @@ -1621,28 +1632,24 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
>
>                 if (ctx)
>                         *ctx = state->indir_desc;
> +

Unnecessary changes.

Thanks






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