On Mon, May 22, 2023 at 10:39:38AM +0300, Arseniy Krasnov wrote:
> This adds handling of MSG_ZEROCOPY flag on transmission path: if this
> flag is set and zerocopy transmission is possible, then non-linear skb
> will be created and filled with the pages of user's buffer. Pages of
> user's buffer are locked in memory by 'get_user_pages()'.
>
> Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> ---
> net/vmw_vsock/virtio_transport_common.c | 305 +++++++++++++++++++-----
> 1 file changed, 243 insertions(+), 62 deletions(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 9854f48a0544..5acf824afe41 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -37,73 +37,161 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
> return container_of(t, struct virtio_transport, transport);
> }
>
> -/* Returns a new packet on success, otherwise returns NULL.
> - *
> - * If NULL is returned, errp is set to a negative errno.
> - */
> -static struct sk_buff *
> -virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> - size_t len,
> - u32 src_cid,
> - u32 src_port,
> - u32 dst_cid,
> - u32 dst_port)
> -{
> - const size_t skb_len = VIRTIO_VSOCK_SKB_HEADROOM + len;
> - struct virtio_vsock_hdr *hdr;
> - struct sk_buff *skb;
> - void *payload;
> - int err;
> +static bool virtio_transport_can_zcopy(struct virtio_vsock_pkt_info *info,
> + size_t max_to_send)
> +{
> + struct iov_iter *iov_iter;
> + size_t max_skb_cap;
> + size_t bytes;
> + int i;
>
> - skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
> - if (!skb)
> - return NULL;
> + if (!info->msg)
> + return false;
>
> - hdr = virtio_vsock_hdr(skb);
> - hdr->type = cpu_to_le16(info->type);
> - hdr->op = cpu_to_le16(info->op);
> - hdr->src_cid = cpu_to_le64(src_cid);
> - hdr->dst_cid = cpu_to_le64(dst_cid);
> - hdr->src_port = cpu_to_le32(src_port);
> - hdr->dst_port = cpu_to_le32(dst_port);
> - hdr->flags = cpu_to_le32(info->flags);
> - hdr->len = cpu_to_le32(len);
> + if (!(info->flags & MSG_ZEROCOPY) && !info->msg->msg_ubuf)
> + return false;
>
> - if (info->msg && len > 0) {
> - payload = skb_put(skb, len);
> - err = memcpy_from_msg(payload, info->msg, len);
> - if (err)
> - goto out;
> + iov_iter = &info->msg->msg_iter;
> +
> + if (iter_is_ubuf(iov_iter)) {
> + if (offset_in_page(iov_iter->ubuf))
> + return false;
> +
> + return true;
> + }
> +
> + if (!iter_is_iovec(iov_iter))
> + return false;
> +
> + if (iov_iter->iov_offset)
> + return false;
> +
> + /* We can't send whole iov. */
> + if (iov_iter->count > max_to_send)
> + return false;
> +
> + for (bytes = 0, i = 0; i < iov_iter->nr_segs; i++) {
> + const struct iovec *iovec;
> + int pages_in_elem;
> +
> + iovec = &iov_iter->__iov[i];
> +
> + /* Base must be page aligned. */
> + if (offset_in_page(iovec->iov_base))
> + return false;
>
> - if (msg_data_left(info->msg) == 0 &&
> - info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
> - hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
> + /* Only last element could have non page aligned size. */
> + if (i != (iov_iter->nr_segs - 1)) {
> + if (offset_in_page(iovec->iov_len))
> + return false;
>
> - if (info->msg->msg_flags & MSG_EOR)
> - hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
> + pages_in_elem = iovec->iov_len >> PAGE_SHIFT;
> + } else {
> + pages_in_elem = round_up(iovec->iov_len, PAGE_SIZE);
> + pages_in_elem >>= PAGE_SHIFT;
> }
> +
> + bytes += (pages_in_elem * PAGE_SIZE);
> }
Hi Arseniy,
bytes is set but the loop above, but seems otherwise unused in this function.
>
> - if (info->reply)
> - virtio_vsock_skb_set_reply(skb);
> + /* How many bytes we can pack to single skb. Maximum packet
> + * buffer size is needed to allow vhost handle such packets,
> + * otherwise they will be dropped.
> + */
> + max_skb_cap = min((unsigned int)(MAX_SKB_FRAGS * PAGE_SIZE),
> + (unsigned int)VIRTIO_VSOCK_MAX_PKT_BUF_SIZE);
Likewise, max_skb_cap seems to be set but unused in this function.
>
> - trace_virtio_transport_alloc_pkt(src_cid, src_port,
> - dst_cid, dst_port,
> - len,
> - info->type,
> - info->op,
> - info->flags);
> + return true;
> +}
...
