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Message-ID: <20200123030712-mutt-send-email-mst@kernel.org>
Date: Thu, 23 Jan 2020 03:26:51 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org, prashantbhole.linux@...il.com,
jasowang@...hat.com, davem@...emloft.net,
jakub.kicinski@...ronome.com, jbrouer@...hat.com, toke@...hat.com,
toshiaki.makita1@...il.com, daniel@...earbox.net,
john.fastabend@...il.com, ast@...nel.org, kafai@...com,
songliubraving@...com, yhs@...com, andriin@...com,
dsahern@...il.com
Subject: Re: [PATCH bpf-next 07/12] vhost_net: user tap recvmsg api to access
ptr ring
On Wed, Jan 22, 2020 at 06:42:05PM -0700, David Ahern wrote:
> From: Prashant Bhole <prashantbhole.linux@...il.com>
>
> Currently vhost_net directly accesses ptr ring of tap driver to
> fetch Rx packet pointers. In order to avoid it this patch modifies
> tap driver's recvmsg api to do additional task of fetching Rx packet
> pointers.
>
> A special struct tun_msg_ctl is already being passed via msg_control
> for tun Rx XDP batching. This patch extends tun_msg_ctl usage to
> send sub commands to recvmsg api. Now tun_recvmsg will handle commands
> to consume and unconsume packet pointers from ptr ring.
>
> This will be useful in implementation of tx path XDP in tun driver,
> where XDP program will process the packet before it is passed to
> vhost_net.
>
> Signed-off-by: Prashant Bhole <prashantbhole.linux@...il.com>
> ---
> drivers/net/tap.c | 22 ++++++++++++++++++-
> drivers/net/tun.c | 24 ++++++++++++++++++++-
> drivers/vhost/net.c | 48 +++++++++++++++++++++++++++++++-----------
> include/linux/if_tun.h | 18 ++++++++++++++++
> 4 files changed, 98 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index a0a5dc18109a..a5ce44db11a3 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -1224,8 +1224,28 @@ static int tap_recvmsg(struct socket *sock, struct msghdr *m,
> size_t total_len, int flags)
> {
> struct tap_queue *q = container_of(sock, struct tap_queue, sock);
> - struct sk_buff *skb = m->msg_control;
> + struct tun_msg_ctl *ctl = m->msg_control;
> + struct sk_buff *skb = NULL;
> int ret;
> +
> + if (ctl) {
> + switch (ctl->type) {
> + case TUN_MSG_PKT:
> + skb = ctl->ptr;
> + break;
> + case TUN_MSG_CONSUME_PKTS:
> + return ptr_ring_consume_batched(&q->ring,
> + ctl->ptr,
> + ctl->num);
> + case TUN_MSG_UNCONSUME_PKTS:
> + ptr_ring_unconsume(&q->ring, ctl->ptr, ctl->num,
> + tun_ptr_free);
> + return 0;
> + default:
> + return -EINVAL;
> + }
> + }
> +
> if (flags & ~(MSG_DONTWAIT|MSG_TRUNC)) {
> kfree_skb(skb);
> return -EINVAL;
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 6f12c32df346..197bde748c09 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2544,7 +2544,8 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
Hmm what about tap_recvmsg then?
> {
> struct tun_file *tfile = container_of(sock, struct tun_file, socket);
> struct tun_struct *tun = tun_get(tfile);
> - void *ptr = m->msg_control;
> + struct tun_msg_ctl *ctl = m->msg_control;
> + void *ptr = NULL;
> int ret;
>
> if (!tun) {
> @@ -2552,6 +2553,27 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
> goto out_free;
> }
>
there's an extra tun_get/tun_put above.
Do we need them?
And if yes isn't tun_ptr_free(ptr) on error a problem?
> + if (ctl) {
> + switch (ctl->type) {
> + case TUN_MSG_PKT:
> + ptr = ctl->ptr;
> + break;
> + case TUN_MSG_CONSUME_PKTS:
> + ret = ptr_ring_consume_batched(&tfile->tx_ring,
> + ctl->ptr,
> + ctl->num);
> + goto out;
> + case TUN_MSG_UNCONSUME_PKTS:
> + ptr_ring_unconsume(&tfile->tx_ring, ctl->ptr,
> + ctl->num, tun_ptr_free);
> + ret = 0;
> + goto out;
> + default:
> + ret = -EINVAL;
> + goto out_put_tun;
> + }
> + }
> +
> if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
> ret = -EINVAL;
> goto out_put_tun;
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index e158159671fa..482548d00105 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -175,24 +175,44 @@ static void *vhost_net_buf_consume(struct vhost_net_buf *rxq)
>
> static int vhost_net_buf_produce(struct vhost_net_virtqueue *nvq)
> {
> + struct vhost_virtqueue *vq = &nvq->vq;
> + struct socket *sock = vq->private_data;
> struct vhost_net_buf *rxq = &nvq->rxq;
> + struct tun_msg_ctl ctl = {
> + .type = TUN_MSG_CONSUME_PKTS,
> + .ptr = (void *) rxq->queue,
> + .num = VHOST_NET_BATCH,
> + };
> + struct msghdr msg = {
> + .msg_control = &ctl,
> + };
>
> rxq->head = 0;
> - rxq->tail = ptr_ring_consume_batched(nvq->rx_ring, rxq->queue,
> - VHOST_NET_BATCH);
> + rxq->tail = sock->ops->recvmsg(sock, &msg, 0, 0);
> + if (WARN_ON_ONCE(rxq->tail < 0))
> + rxq->tail = 0;
> +
> return rxq->tail;
> }
Hmm isn't there a way to avoid an indirect call here on data path?
ptr ring is a tun/tap thing anyway ...
>
> static void vhost_net_buf_unproduce(struct vhost_net_virtqueue *nvq)
> {
> + struct vhost_virtqueue *vq = &nvq->vq;
> + struct socket *sock = vq->private_data;
> struct vhost_net_buf *rxq = &nvq->rxq;
> + struct tun_msg_ctl ctl = {
> + .type = TUN_MSG_UNCONSUME_PKTS,
> + .ptr = (void *) (rxq->queue + rxq->head),
You don't really need to cast to void. An assignment will do.
> + .num = vhost_net_buf_get_size(rxq),
> + };
> + struct msghdr msg = {
> + .msg_control = &ctl,
> + };
>
> - if (nvq->rx_ring && !vhost_net_buf_is_empty(rxq)) {
> - ptr_ring_unconsume(nvq->rx_ring, rxq->queue + rxq->head,
> - vhost_net_buf_get_size(rxq),
> - tun_ptr_free);
> - rxq->head = rxq->tail = 0;
> - }
> + if (!vhost_net_buf_is_empty(rxq))
> + sock->ops->recvmsg(sock, &msg, 0, 0);
> +
> + rxq->head = rxq->tail = 0;
> }
>
> static int vhost_net_buf_peek_len(void *ptr)
> @@ -1109,6 +1129,7 @@ static void handle_rx(struct vhost_net *net)
> .flags = 0,
> .gso_type = VIRTIO_NET_HDR_GSO_NONE
> };
> + struct tun_msg_ctl ctl;
> size_t total_len = 0;
> int err, mergeable;
> s16 headcount;
> @@ -1166,8 +1187,11 @@ static void handle_rx(struct vhost_net *net)
> goto out;
> }
> busyloop_intr = false;
> - if (nvq->rx_ring)
> - msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
> + if (nvq->rx_ring) {
> + ctl.type = TUN_MSG_PKT;
> + ctl.ptr = vhost_net_buf_consume(&nvq->rxq);
> + msg.msg_control = &ctl;
> + }
> /* On overrun, truncate and discard */
> if (unlikely(headcount > UIO_MAXIOV)) {
> iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
> @@ -1346,8 +1370,8 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
> mutex_lock(&vq->mutex);
> sock = vq->private_data;
> vhost_net_disable_vq(n, vq);
> - vq->private_data = NULL;
> vhost_net_buf_unproduce(nvq);
> + vq->private_data = NULL;
> nvq->rx_ring = NULL;
So is rx_ring still in use?
> mutex_unlock(&vq->mutex);
> return sock;
> @@ -1538,8 +1562,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
> }
>
> vhost_net_disable_vq(n, vq);
> - vq->private_data = sock;
> vhost_net_buf_unproduce(nvq);
> + vq->private_data = sock;
> r = vhost_vq_init_access(vq);
> if (r)
> goto err_used;
> diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
> index 49ca20063a35..9184e3f177b8 100644
> --- a/include/linux/if_tun.h
> +++ b/include/linux/if_tun.h
> @@ -12,8 +12,26 @@
>
> #define TUN_XDP_FLAG 0x1UL
>
> +/*
> + * tun_msg_ctl types
> + */
> +
> #define TUN_MSG_UBUF 1
> #define TUN_MSG_PTR 2
> +/*
> + * Used for passing a packet pointer from vhost to tun
> + */
> +#define TUN_MSG_PKT 3
> +/*
> + * Used for passing an array of pointer from vhost to tun.
> + * tun consumes packets from ptr ring and stores in pointer array.
> + */
> +#define TUN_MSG_CONSUME_PKTS 4
> +/*
> + * Used for passing an array of pointer from vhost to tun.
> + * tun consumes get pointer from array and puts back into ptr ring.
> + */
> +#define TUN_MSG_UNCONSUME_PKTS 5
> struct tun_msg_ctl {
> unsigned short type;
> unsigned short num;
> --
> 2.21.1 (Apple Git-122.3)
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