Subject: Re: [PATCHv7] add mergeable buffers support to vhost_net

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 4 May 2010 01:48:23 +0300

On Wed, Apr 28, 2010 at 01:57:12PM -0700, David L Stevens wrote:
> This patch adds mergeable receive buffer support to vhost_net.
> 
> Signed-off-by: David L Stevens <[email-masked]>
> 
> diff -ruNp net-next-v0/drivers/vhost/net.c net-next-v7/drivers/vhost/net.c
> --- net-next-v0/drivers/vhost/net.c	2010-04-24 21:36:54.000000000 -0700
> +++ net-next-v7/drivers/vhost/net.c	2010-04-28 12:26:18.000000000 -0700
> @@ -74,6 +74,23 @@ static int move_iovec_hdr(struct iovec *
>  	}
>  	return seg;
>  }
> +/* Copy iovec entries for len bytes from iovec. Return segments used. */
> +static int copy_iovec_hdr(const struct iovec *from, struct iovec *to,
> +			  size_t len, int iovcount)
> +{
> +	int seg = 0;
> +	size_t size;
> +	while (len && seg < iovcount) {
> +		size = min(from->iov_len, len);
> +		to->iov_base = from->iov_base;
> +		to->iov_len = size;
> +		len -= size;
> +		++from;
> +		++to;
> +		++seg;
> +	}
> +	return seg;
> +}
>  
>  /* Caller must have TX VQ lock */
>  static void tx_poll_stop(struct vhost_net *net)
> @@ -109,7 +126,7 @@ static void handle_tx(struct vhost_net *
>  	};
>  	size_t len, total_len = 0;
>  	int err, wmem;
> -	size_t hdr_size;
> +	size_t vhost_hlen;
>  	struct socket *sock = rcu_dereference(vq->private_data);
>  	if (!sock)
>  		return;
> @@ -128,13 +145,13 @@ static void handle_tx(struct vhost_net *
>  
>  	if (wmem < sock->sk->sk_sndbuf / 2)
>  		tx_poll_stop(net);
> -	hdr_size = vq->hdr_size;
> +	vhost_hlen = vq->vhost_hlen;
>  
>  	for (;;) {
> -		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
> -					 ARRAY_SIZE(vq->iov),
> -					 &out, &in,
> -					 NULL, NULL);
> +		head = vhost_get_desc(&net->dev, vq, vq->iov,
> +				      ARRAY_SIZE(vq->iov),
> +				      &out, &in,
> +				      NULL, NULL);
>  		/* Nothing new?  Wait for eventfd to tell us they refilled. */
>  		if (head == vq->num) {
>  			wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> @@ -155,20 +172,20 @@ static void handle_tx(struct vhost_net *
>  			break;
>  		}
>  		/* Skip header. TODO: support TSO. */
> -		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, out);
> +		s = move_iovec_hdr(vq->iov, vq->hdr, vhost_hlen, out);
>  		msg.msg_iovlen = out;
>  		len = iov_length(vq->iov, out);
>  		/* Sanity check */
>  		if (!len) {
>  			vq_err(vq, "Unexpected header len for TX: "
>  			       "%zd expected %zd\n",
> -			       iov_length(vq->hdr, s), hdr_size);
> +			       iov_length(vq->hdr, s), vhost_hlen);
>  			break;
>  		}
>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(NULL, sock, &msg, len);
>  		if (unlikely(err < 0)) {
> -			vhost_discard_vq_desc(vq);
> +			vhost_discard_desc(vq, 1);
>  			tx_poll_start(net, sock);
>  			break;
>  		}
> @@ -187,12 +204,25 @@ static void handle_tx(struct vhost_net *
>  	unuse_mm(net->dev.mm);
>  }
>  
> +static int vhost_head_len(struct vhost_virtqueue *vq, struct sock *sk)
> +{
> +	struct sk_buff *head;
> +	int len = 0;
> +
> +	lock_sock(sk);
> +	head = skb_peek(&sk->sk_receive_queue);
> +	if (head)
> +		len = head->len + vq->sock_hlen;
> +	release_sock(sk);
> +	return len;
> +}
> +
>  /* Expects to be always run from workqueue - which acts as
>   * read-size critical section for our kind of RCU. */
>  static void handle_rx(struct vhost_net *net)
>  {
>  	struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
> -	unsigned head, out, in, log, s;
> +	unsigned in, log, s;
>  	struct vhost_log *vq_log;
>  	struct msghdr msg = {
>  		.msg_name = NULL,
> @@ -203,14 +233,14 @@ static void handle_rx(struct vhost_net *
>  		.msg_flags = MSG_DONTWAIT,
>  	};
>  
> -	struct virtio_net_hdr hdr = {
> -		.flags = 0,
> -		.gso_type = VIRTIO_NET_HDR_GSO_NONE
> +	struct virtio_net_hdr_mrg_rxbuf hdr = {
> +		.hdr.flags = 0,
> +		.hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
>  	};
>  
>  	size_t len, total_len = 0;
> -	int err;
> -	size_t hdr_size;
> +	int err, headcount, datalen;
> +	size_t vhost_hlen;
>  	struct socket *sock = rcu_dereference(vq->private_data);
>  	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
>  		return;
> @@ -218,18 +248,19 @@ static void handle_rx(struct vhost_net *
>  	use_mm(net->dev.mm);
>  	mutex_lock(&vq->mutex);
>  	vhost_disable_notify(vq);
> -	hdr_size = vq->hdr_size;
> +	vhost_hlen = vq->vhost_hlen;
>  
>  	vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
>  		vq->log : NULL;
>  
> -	for (;;) {
> -		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
> -					 ARRAY_SIZE(vq->iov),
> -					 &out, &in,
> -					 vq_log, &log);
> +	while ((datalen = vhost_head_len(vq, sock->sk))) {
> +		headcount = vhost_get_desc_n(vq, vq->heads,
> +					     datalen + vhost_hlen,
> +					     &in, vq_log, &log);
> +		if (headcount < 0)
> +			break;
>  		/* OK, now we need to know about added descriptors. */
> -		if (head == vq->num) {
> +		if (!headcount) {
>  			if (unlikely(vhost_enable_notify(vq))) {
>  				/* They have slipped one in as we were
>  				 * doing that: check again. */
> @@ -241,46 +272,53 @@ static void handle_rx(struct vhost_net *
>  			break;
>  		}
>  		/* We don't need to be notified again. */
> -		if (out) {
> -			vq_err(vq, "Unexpected descriptor format for RX: "
> -			       "out %d, int %d\n",
> -			       out, in);
> -			break;
> -		}
> -		/* Skip header. TODO: support TSO/mergeable rx buffers. */
> -		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, in);
> +		if (vhost_hlen)
> +			/* Skip header. TODO: support TSO. */
> +			s = move_iovec_hdr(vq->iov, vq->hdr, vhost_hlen, in);
> +		else
> +			s = copy_iovec_hdr(vq->iov, vq->hdr, vq->sock_hlen, in);
>  		msg.msg_iovlen = in;
>  		len = iov_length(vq->iov, in);
>  		/* Sanity check */
>  		if (!len) {
>  			vq_err(vq, "Unexpected header len for RX: "
>  			       "%zd expected %zd\n",
> -			       iov_length(vq->hdr, s), hdr_size);
> +			       iov_length(vq->hdr, s), vhost_hlen);
>  			break;
>  		}
>  		err = sock->ops->recvmsg(NULL, sock, &msg,
>  					 len, MSG_DONTWAIT | MSG_TRUNC);
>  		/* TODO: Check specific error and bomb out unless EAGAIN? */
>  		if (err < 0) {
> -			vhost_discard_vq_desc(vq);
> +			vhost_discard_desc(vq, headcount);
>  			break;
>  		}
> -		/* TODO: Should check and handle checksum. */
> -		if (err > len) {
> -			pr_err("Discarded truncated rx packet: "
> -			       " len %d > %zd\n", err, len);
> -			vhost_discard_vq_desc(vq);
> +		if (err != datalen) {
> +			pr_err("Discarded rx packet: "
> +			       " len %d, expected %zd\n", err, datalen);
> +			vhost_discard_desc(vq, headcount);
>  			continue;
>  		}
>  		len = err;
> -		err = memcpy_toiovec(vq->hdr, (unsigned char *)&hdr, hdr_size);
> -		if (err) {
> -			vq_err(vq, "Unable to write vnet_hdr at addr %p: %d\n",
> -			       vq->iov->iov_base, err);
> +		if (vhost_hlen &&
> +		    memcpy_toiovecend(vq->hdr, (unsigned char *)&hdr, 0,
> +				      vhost_hlen)) {
> +			vq_err(vq, "Unable to write vnet_hdr at addr %p\n",
> +			       vq->iov->iov_base);
>  			break;
>  		}
> -		len += hdr_size;
> -		vhost_add_used_and_signal(&net->dev, vq, head, len);
> +		/* TODO: Should check and handle checksum. */
> +		if (vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF) &&
> +		    memcpy_toiovecend(vq->hdr, (unsigned char *)&headcount,
> +				      offsetof(typeof(hdr), num_buffers),
> +				      sizeof(hdr.num_buffers))) {
> +			vq_err(vq, "Failed num_buffers write");
> +			vhost_discard_desc(vq, headcount);
> +			break;
> +		}
> +		len += vhost_hlen;
> +		vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> +					    headcount);
>  		if (unlikely(vq_log))
>  			vhost_log_write(vq, vq_log, log, len);
>  		total_len += len;
> @@ -561,9 +599,21 @@ done:
>  
>  static int vhost_net_set_features(struct vhost_net *n, u64 features)
>  {
> -	size_t hdr_size = features & (1 << VHOST_NET_F_VIRTIO_NET_HDR) ?
> -		sizeof(struct virtio_net_hdr) : 0;
> +	size_t vhost_hlen, sock_hlen, hdr_len;
>  	int i;
> +
> +	hdr_len = (features & (1 << VIRTIO_NET_F_MRG_RXBUF)) ?
> +			sizeof(struct virtio_net_hdr_mrg_rxbuf) :
> +			sizeof(struct virtio_net_hdr);
> +	if (features & (1 << VHOST_NET_F_VIRTIO_NET_HDR)) {
> +		/* vhost provides vnet_hdr */
> +		vhost_hlen = hdr_len;
> +		sock_hlen = 0;
> +	} else {
> +		/* socket provides vnet_hdr */
> +		vhost_hlen = 0;
> +		sock_hlen = hdr_len;
> +	}
>  	mutex_lock(&n->dev.mutex);
>  	if ((features & (1 << VHOST_F_LOG_ALL)) &&
>  	    !vhost_log_access_ok(&n->dev)) {
> @@ -574,7 +624,8 @@ static int vhost_net_set_features(struct
>  	smp_wmb();
>  	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
>  		mutex_lock(&n->vqs[i].mutex);
> -		n->vqs[i].hdr_size = hdr_size;
> +		n->vqs[i].vhost_hlen = vhost_hlen;
> +		n->vqs[i].sock_hlen = sock_hlen;
>  		mutex_unlock(&n->vqs[i].mutex);
>  	}
>  	vhost_net_flush(n);
> diff -ruNp net-next-v0/drivers/vhost/vhost.c net-next-v7/drivers/vhost/vhost.c
> --- net-next-v0/drivers/vhost/vhost.c	2010-04-22 11:31:57.000000000 -0700
> +++ net-next-v7/drivers/vhost/vhost.c	2010-04-28 11:16:13.000000000 -0700
> @@ -114,7 +114,8 @@ static void vhost_vq_reset(struct vhost_
>  	vq->used_flags = 0;
>  	vq->log_used = false;
>  	vq->log_addr = -1ull;
> -	vq->hdr_size = 0;
> +	vq->vhost_hlen = 0;
> +	vq->sock_hlen = 0;
>  	vq->private_data = NULL;
>  	vq->log_base = NULL;
>  	vq->error_ctx = NULL;
> @@ -861,6 +862,53 @@ static unsigned get_indirect(struct vhos
>  	return 0;
>  }
>  
> +/* This is a multi-buffer version of vhost_get_desc
> + * @vq		- the relevant virtqueue
> + * datalen	- data length we'll be reading
> + * @iovcount	- returned count of io vectors we fill
> + * @log		- vhost log
> + * @log_num	- log offset
> + *	returns number of buffer heads allocated, negative on error
> + */
> +int vhost_get_desc_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
> +		     int datalen, unsigned *iovcount, struct vhost_log *log,
> +		     unsigned int *log_num)
> +{
> +	unsigned int out, in;
> +	int seg = 0;
> +	int headcount = 0;
> +	int r;
> +
> +	while (datalen > 0) {
> +		if (headcount >= VHOST_NET_MAX_SG) {
> +			r = -ENOBUFS;
> +			goto err;
> +		}
> +		heads[headcount].id = vhost_get_desc(vq->dev, vq, vq->iov + seg,
> +					      ARRAY_SIZE(vq->iov) - seg, &out,
> +					      &in, log, log_num);

By the way, logging here looks broken to me.
Does live migration work for you?

log_num gets zeroed out on each call to vhost_get_desc.
I guess we could just change vhost_get_desc not to zero out
log_num at the start, do it here instead,
and pass in log + *log_num instead of log_num.

Need to also document the API for vhost_get_desc noting
that log_num is incremented, not stored to.

Pls think about it.

> +		if (heads[headcount].id == vq->num) {
> +			r = 0;
> +			goto err;
> +		}
> +		if (out || in <= 0) {
> +			vq_err(vq, "unexpected descriptor format for RX: "
> +				"out %d, in %d\n", out, in);
> +			r = -EINVAL;
> +			goto err;
> +		}
> +		heads[headcount].len = iov_length(vq->iov + seg, in);
> +		datalen -= heads[headcount].len;
> +		++headcount;
> +		seg += in;
> +	}
> +	*iovcount = seg;
> +	return headcount;
> +err:
> +	vhost_discard_desc(vq, headcount);
> +	return r;
> +}
> +
>  /* This looks in the virtqueue and for the first available buffer, and converts
>   * it to an iovec for convenient access.  Since descriptors consist of some
>   * number of output then some number of input descriptors, it's actually two
> @@ -868,7 +916,7 @@ static unsigned get_indirect(struct vhos
>   *
>   * This function returns the descriptor number found, or vq->num (which
>   * is never a valid descriptor number) if none was found. */
> -unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> +unsigned vhost_get_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
>  			   struct iovec iov[], unsigned int iov_size,
>  			   unsigned int *out_num, unsigned int *in_num,
>  			   struct vhost_log *log, unsigned int *log_num)
> @@ -986,9 +1034,9 @@ unsigned vhost_get_vq_desc(struct vhost_
>  }
>  
>  /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
> -void vhost_discard_vq_desc(struct vhost_virtqueue *vq)
> +void vhost_discard_desc(struct vhost_virtqueue *vq, int n)
>  {
> -	vq->last_avail_idx--;
> +	vq->last_avail_idx -= n;
>  }
>  
>  /* After we've used one of their buffers, we tell them about it.  We'll then
> @@ -1033,6 +1081,68 @@ int vhost_add_used(struct vhost_virtqueu
>  	return 0;
>  }
>  
> +static void vhost_log_used(struct vhost_virtqueue *vq,
> +			   struct vring_used_elem __user *used)
> +{
> +	/* Make sure data is seen before log. */
> +	smp_wmb();
> +	/* Log used ring entry write. */
> +	log_write(vq->log_base,
> +		  vq->log_addr +
> +		   ((void __user *)used - (void __user *)vq->used),
> +		  sizeof *used);
> +	/* Log used index update. */
> +	log_write(vq->log_base,
> +		  vq->log_addr + offsetof(struct vring_used, idx),
> +		  sizeof vq->used->idx);
> +	if (vq->log_ctx)
> +		eventfd_signal(vq->log_ctx, 1);
> +}
> +
> +static int __vhost_add_used_n(struct vhost_virtqueue *vq,
> +			    struct vring_used_elem *heads,
> +			    unsigned count)
> +{
> +	struct vring_used_elem __user *used;
> +	int start;
> +
> +	start = vq->last_used_idx % vq->num;
> +	used = vq->used->ring + start;
> +	if (copy_to_user(used, heads, count * sizeof *used)) {
> +		vq_err(vq, "Failed to write used");
> +		return -EFAULT;
> +	}
> +	/* Make sure buffer is written before we update index. */
> +	smp_wmb();
> +	if (put_user(vq->last_used_idx + count, &vq->used->idx)) {
> +		vq_err(vq, "Failed to increment used idx");
> +		return -EFAULT;
> +	}
> +	if (unlikely(vq->log_used))
> +		vhost_log_used(vq, used);
> +	vq->last_used_idx += count;
> +	return 0;
> +}
> +
> +/* After we've used one of their buffers, we tell them about it.  We'll then
> + * want to notify the guest, using eventfd. */
> +int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
> +		     unsigned count)
> +{
> +	int start, n, r;
> +
> +	start = vq->last_used_idx % vq->num;
> +	n = vq->num - start;
> +	if (n < count) {
> +		r = __vhost_add_used_n(vq, heads, n);
> +		if (r < 0)
> +			return r;
> +		heads += n;
> +		count -= n;
> +	}
> +	return __vhost_add_used_n(vq, heads, count);
> +}
> +
>  /* This actually signals the guest, using eventfd. */
>  void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>  {
> @@ -1062,6 +1172,15 @@ void vhost_add_used_and_signal(struct vh
>  	vhost_signal(dev, vq);
>  }
>  
> +/* multi-buffer version of vhost_add_used_and_signal */
> +void vhost_add_used_and_signal_n(struct vhost_dev *dev,
> +				 struct vhost_virtqueue *vq,
> +				 struct vring_used_elem *heads, unsigned count)
> +{
> +	vhost_add_used_n(vq, heads, count);
> +	vhost_signal(dev, vq);
> +}
> +
>  /* OK, now we need to know about added descriptors. */
>  bool vhost_enable_notify(struct vhost_virtqueue *vq)
>  {
> @@ -1086,7 +1205,7 @@ bool vhost_enable_notify(struct vhost_vi
>  		return false;
>  	}
>  
> -	return avail_idx != vq->last_avail_idx;
> +	return avail_idx != vq->avail_idx;
>  }
>  
>  /* We don't need to be notified again. */
> diff -ruNp net-next-v0/drivers/vhost/vhost.h net-next-v7/drivers/vhost/vhost.h
> --- net-next-v0/drivers/vhost/vhost.h	2010-04-24 21:37:41.000000000 -0700
> +++ net-next-v7/drivers/vhost/vhost.h	2010-04-26 10:35:25.000000000 -0700
> @@ -84,7 +84,9 @@ struct vhost_virtqueue {
>  	struct iovec indirect[VHOST_NET_MAX_SG];
>  	struct iovec iov[VHOST_NET_MAX_SG];
>  	struct iovec hdr[VHOST_NET_MAX_SG];
> -	size_t hdr_size;
> +	size_t vhost_hlen;
> +	size_t sock_hlen;
> +	struct vring_used_elem heads[VHOST_NET_MAX_SG];
>  	/* We use a kind of RCU to access private pointer.
>  	 * All readers access it from workqueue, which makes it possible to
>  	 * flush the workqueue instead of synchronize_rcu. Therefore readers do
> @@ -120,16 +122,23 @@ long vhost_dev_ioctl(struct vhost_dev *,
>  int vhost_vq_access_ok(struct vhost_virtqueue *vq);
>  int vhost_log_access_ok(struct vhost_dev *);
>  
> -unsigned vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
> +int vhost_get_desc_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
> +		     int datalen, unsigned int *iovcount, struct vhost_log *log,
> +		     unsigned int *log_num);
> +unsigned vhost_get_desc(struct vhost_dev *, struct vhost_virtqueue *,
>  			   struct iovec iov[], unsigned int iov_count,
>  			   unsigned int *out_num, unsigned int *in_num,
>  			   struct vhost_log *log, unsigned int *log_num);
> -void vhost_discard_vq_desc(struct vhost_virtqueue *);
> +void vhost_discard_desc(struct vhost_virtqueue *, int);
>  
>  int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
> -void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
> +int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
> +		     unsigned count);
>  void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
> -			       unsigned int head, int len);
> +			       unsigned int id, int len);
> +void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
> +			       struct vring_used_elem *heads, unsigned count);
> +void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
>  void vhost_disable_notify(struct vhost_virtqueue *);
>  bool vhost_enable_notify(struct vhost_virtqueue *);
>  
> @@ -149,7 +158,8 @@ enum {
>  	VHOST_FEATURES = (1 << VIRTIO_F_NOTIFY_ON_EMPTY) |
>  			 (1 << VIRTIO_RING_F_INDIRECT_DESC) |
>  			 (1 << VHOST_F_LOG_ALL) |
> -			 (1 << VHOST_NET_F_VIRTIO_NET_HDR),
> +			 (1 << VHOST_NET_F_VIRTIO_NET_HDR) |
> +			 (1 << VIRTIO_NET_F_MRG_RXBUF),
>  };
>  
>  static inline int vhost_has_feature(struct vhost_dev *dev, int bit)
>