Message-ID: <8c2343fc-0517-8436-7abb-a2f69881cea7@sberdevices.ru>
Date: Tue, 25 Jul 2023 16:04:13 +0300
From: Arseniy Krasnov <avkrasnov@...rdevices.ru>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella
	<sgarzare@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Jason Wang <jasowang@...hat.com>, Bobby Eshleman
	<bobby.eshleman@...edance.com>, <kvm@...r.kernel.org>,
	<virtualization@...ts.linux-foundation.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kernel@...rdevices.ru>, <oxffffaa@...il.com>
Subject: Re: [PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support



On 25.07.2023 14:50, Michael S. Tsirkin wrote:
> On Fri, Jul 21, 2023 at 08:09:03AM +0300, Arseniy Krasnov wrote:
>>
>>
>> On 21.07.2023 00:42, Arseniy Krasnov wrote:
>>> This adds handling of MSG_ZEROCOPY flag on transmission path: if this
>>> flag is set and zerocopy transmission is possible (enabled in socket
>>> options and transport allows zerocopy), 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()'. Second thing that
>>> this patch does is replace type of skb owning: instead of calling
>>> 'skb_set_owner_sk_safe()' it calls 'skb_set_owner_w()'. Reason of this
>>> change is that '__zerocopy_sg_from_iter()' increments 'sk_wmem_alloc'
>>> of socket, so to decrease this field correctly proper skb destructor is
>>> needed: 'sock_wfree()'. This destructor is set by 'skb_set_owner_w()'.
>>>
>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>>> ---
>>>  Changelog:
>>>  v5(big patchset) -> v1:
>>>   * Refactorings of 'if' conditions.
>>>   * Remove extra blank line.
>>>   * Remove 'frag_off' field unneeded init.
>>>   * Add function 'virtio_transport_fill_skb()' which fills both linear
>>>     and non-linear skb with provided data.
>>>  v1 -> v2:
>>>   * Use original order of last four arguments in 'virtio_transport_alloc_skb()'.
>>>  v2 -> v3:
>>>   * Add new transport callback: 'msgzerocopy_check_iov'. It checks that
>>>     provided 'iov_iter' with data could be sent in a zerocopy mode.
>>>     If this callback is not set in transport - transport allows to send
>>>     any 'iov_iter' in zerocopy mode. Otherwise - if callback returns 'true'
>>>     then zerocopy is allowed. Reason of this callback is that in case of
>>>     G2H transmission we insert whole skb to the tx virtio queue and such
>>>     skb must fit to the size of the virtio queue to be sent in a single
>>>     iteration (may be tx logic in 'virtio_transport.c' could be reworked
>>>     as in vhost to support partial send of current skb). This callback
>>>     will be enabled only for G2H path. For details pls see comment 
>>>     'Check that tx queue...' below.
>>>
>>>  include/net/af_vsock.h                  |   3 +
>>>  net/vmw_vsock/virtio_transport.c        |  39 ++++
>>>  net/vmw_vsock/virtio_transport_common.c | 257 ++++++++++++++++++------
>>>  3 files changed, 241 insertions(+), 58 deletions(-)
>>>
>>> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>>> index 0e7504a42925..a6b346eeeb8e 100644
>>> --- a/include/net/af_vsock.h
>>> +++ b/include/net/af_vsock.h
>>> @@ -177,6 +177,9 @@ struct vsock_transport {
>>>  
>>>  	/* Read a single skb */
>>>  	int (*read_skb)(struct vsock_sock *, skb_read_actor_t);
>>> +
>>> +	/* Zero-copy. */
>>> +	bool (*msgzerocopy_check_iov)(const struct iov_iter *);
>>>  };
>>>  
>>>  /**** CORE ****/
>>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>>> index 7bbcc8093e51..23cb8ed638c4 100644
>>> --- a/net/vmw_vsock/virtio_transport.c
>>> +++ b/net/vmw_vsock/virtio_transport.c
>>> @@ -442,6 +442,43 @@ static void virtio_vsock_rx_done(struct virtqueue *vq)
>>>  	queue_work(virtio_vsock_workqueue, &vsock->rx_work);
>>>  }
>>>  
>>> +static bool virtio_transport_msgzerocopy_check_iov(const struct iov_iter *iov)
>>> +{
>>> +	struct virtio_vsock *vsock;
>>> +	bool res = false;
>>> +
>>> +	rcu_read_lock();
>>> +
>>> +	vsock = rcu_dereference(the_virtio_vsock);
>>> +	if (vsock) {
>>> +		struct virtqueue *vq;
>>> +		int iov_pages;
>>> +
>>> +		vq = vsock->vqs[VSOCK_VQ_TX];
>>> +
>>> +		iov_pages = round_up(iov->count, PAGE_SIZE) / PAGE_SIZE;
>>> +
>>> +		/* Check that tx queue is large enough to keep whole
>>> +		 * data to send. This is needed, because when there is
>>> +		 * not enough free space in the queue, current skb to
>>> +		 * send will be reinserted to the head of tx list of
>>> +		 * the socket to retry transmission later, so if skb
>>> +		 * is bigger than whole queue, it will be reinserted
>>> +		 * again and again, thus blocking other skbs to be sent.
>>> +		 * Each page of the user provided buffer will be added
>>> +		 * as a single buffer to the tx virtqueue, so compare
>>> +		 * number of pages against maximum capacity of the queue.
>>> +		 * +1 means buffer for the packet header.
>>> +		 */
>>> +		if (iov_pages + 1 <= vq->num_max)
>>
>> I think this check is actual only for case one we don't have indirect buffer feature.
>> With indirect mode whole data to send will be packed into one indirect buffer.
>>
>> Thanks, Arseniy
> 
> Actually the reverse. With indirect you are limited to num_max.
> Without you are limited to whatever space is left in the
> queue (which you did not check here, so you should).

I mean that with indirect, we only need one buffer, and we can just wait
for enough space - for this single buffer ( as we discussed a little bit before).
But if indirect buffer is not supported - we need that whole packet must fit
to the size of tx queue - otherwise it never be transmitted.

Thanks, Arseniy

> 
> 
>>> +			res = true;
>>> +	}
>>> +
>>> +	rcu_read_unlock();
> 
> Just curious:
> is the point of all this RCU dance to allow vsock
> to change from under us? then why is it ok to
> have it change? the virtio_transport_msgzerocopy_check_iov
> will then refer to the old vsock ...
> 
> 
>>> +
>>> +	return res;
>>> +}
>>> +
>>>  static bool virtio_transport_seqpacket_allow(u32 remote_cid);
>>>  
>>>  static struct virtio_transport virtio_transport = {
>>> @@ -475,6 +512,8 @@ static struct virtio_transport virtio_transport = {
>>>  		.seqpacket_allow          = virtio_transport_seqpacket_allow,
>>>  		.seqpacket_has_data       = virtio_transport_seqpacket_has_data,
>>>  
>>> +		.msgzerocopy_check_iov	  = virtio_transport_msgzerocopy_check_iov,
>>> +
>>>  		.notify_poll_in           = virtio_transport_notify_poll_in,
>>>  		.notify_poll_out          = virtio_transport_notify_poll_out,
>>>  		.notify_recv_init         = virtio_transport_notify_recv_init,
>>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>>> index 26a4d10da205..e4e3d541aff4 100644
>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>> @@ -37,73 +37,122 @@ 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)
>>> +{
>>> +	const struct vsock_transport *t;
>>> +	struct iov_iter *iov_iter;
>>>  
>>> -	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);
>>> +	iov_iter = &info->msg->msg_iter;
>>>  
>>> -	if (info->msg && len > 0) {
>>> -		payload = skb_put(skb, len);
>>> -		err = memcpy_from_msg(payload, info->msg, len);
>>> -		if (err)
>>> -			goto out;
>>> +	t = vsock_core_get_transport(info->vsk);
>>>  
>>> -		if (msg_data_left(info->msg) == 0 &&
>>> -		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
>>> -			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>>> +	if (t->msgzerocopy_check_iov &&
>>> +	    !t->msgzerocopy_check_iov(iov_iter))
>>> +		return false;
>>>  
>>> -			if (info->msg->msg_flags & MSG_EOR)
>>> -				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>>> -		}
>>> +	/* Data is simple buffer. */
>>> +	if (iter_is_ubuf(iov_iter))
>>> +		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;
>>> +
>>> +	return true;
>>> +}
>>> +
>>> +static int virtio_transport_init_zcopy_skb(struct vsock_sock *vsk,
>>> +					   struct sk_buff *skb,
>>> +					   struct msghdr *msg,
>>> +					   bool zerocopy)
>>> +{
>>> +	struct ubuf_info *uarg;
>>> +
>>> +	if (msg->msg_ubuf) {
>>> +		uarg = msg->msg_ubuf;
>>> +		net_zcopy_get(uarg);
>>> +	} else {
>>> +		struct iov_iter *iter = &msg->msg_iter;
>>> +		struct ubuf_info_msgzc *uarg_zc;
>>> +		int len;
>>> +
>>> +		/* Only ITER_IOVEC or ITER_UBUF are allowed and
>>> +		 * checked before.
>>> +		 */
>>> +		if (iter_is_iovec(iter))
>>> +			len = iov_length(iter->__iov, iter->nr_segs);
>>> +		else
>>> +			len = iter->count;
>>> +
>>> +		uarg = msg_zerocopy_realloc(sk_vsock(vsk),
>>> +					    len,
>>> +					    NULL);
>>> +		if (!uarg)
>>> +			return -1;
>>> +
>>> +		uarg_zc = uarg_to_msgzc(uarg);
>>> +		uarg_zc->zerocopy = zerocopy ? 1 : 0;
>>>  	}
>>>  
>>> -	if (info->reply)
>>> -		virtio_vsock_skb_set_reply(skb);
>>> +	skb_zcopy_init(skb, uarg);
>>>  
>>> -	trace_virtio_transport_alloc_pkt(src_cid, src_port,
>>> -					 dst_cid, dst_port,
>>> -					 len,
>>> -					 info->type,
>>> -					 info->op,
>>> -					 info->flags);
>>> +	return 0;
>>> +}
>>>  
>>> -	if (info->vsk && !skb_set_owner_sk_safe(skb, sk_vsock(info->vsk))) {
>>> -		WARN_ONCE(1, "failed to allocate skb on vsock socket with sk_refcnt == 0\n");
>>> -		goto out;
>>> +static int virtio_transport_fill_skb(struct sk_buff *skb,
>>> +				     struct virtio_vsock_pkt_info *info,
>>> +				     size_t len,
>>> +				     bool zcopy)
>>> +{
>>> +	if (zcopy) {
>>> +		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
>>> +					      &info->msg->msg_iter,
>>> +					      len);
>>> +	} else {
>>> +		void *payload;
>>> +		int err;
>>> +
>>> +		payload = skb_put(skb, len);
>>> +		err = memcpy_from_msg(payload, info->msg, len);
>>> +		if (err)
>>> +			return -1;
>>> +
>>> +		if (msg_data_left(info->msg))
>>> +			return 0;
>>> +
>>> +		return 0;
>>>  	}
>>> +}
>>>  
>>> -	return skb;
>>> +static void virtio_transport_init_hdr(struct sk_buff *skb,
>>> +				      struct virtio_vsock_pkt_info *info,
>>> +				      u32 src_cid,
>>> +				      u32 src_port,
>>> +				      u32 dst_cid,
>>> +				      u32 dst_port,
>>> +				      size_t len)
>>> +{
>>> +	struct virtio_vsock_hdr *hdr;
>>>  
>>> -out:
>>> -	kfree_skb(skb);
>>> -	return NULL;
>>> +	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);
>>>  }
>>>  
>>>  static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb,
>>> @@ -214,6 +263,70 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>>  		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>>>  }
>>>  
>>> +static struct sk_buff *virtio_transport_alloc_skb(struct vsock_sock *vsk,
>>> +						  struct virtio_vsock_pkt_info *info,
>>> +						  size_t payload_len,
>>> +						  bool zcopy,
>>> +						  u32 src_cid,
>>> +						  u32 src_port,
>>> +						  u32 dst_cid,
>>> +						  u32 dst_port)
>>> +{
>>> +	struct sk_buff *skb;
>>> +	size_t skb_len;
>>> +
>>> +	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
>>> +
>>> +	if (!zcopy)
>>> +		skb_len += payload_len;
>>> +
>>> +	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>>> +	if (!skb)
>>> +		return NULL;
>>> +
>>> +	virtio_transport_init_hdr(skb, info, src_cid, src_port,
>>> +				  dst_cid, dst_port,
>>> +				  payload_len);
>>> +
>>> +	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
>>> +	 * owner of skb without check to update 'sk_wmem_alloc'.
>>> +	 */
>>> +	if (vsk)
>>> +		skb_set_owner_w(skb, sk_vsock(vsk));
>>> +
>>> +	if (info->msg && payload_len > 0) {
>>> +		int err;
>>> +
>>> +		err = virtio_transport_fill_skb(skb, info, payload_len, zcopy);
>>> +		if (err)
>>> +			goto out;
>>> +
>>> +		if (info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
>>> +			struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
>>> +
>>> +			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>>> +
>>> +			if (info->msg->msg_flags & MSG_EOR)
>>> +				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
>>> +		}
>>> +	}
>>> +
>>> +	if (info->reply)
>>> +		virtio_vsock_skb_set_reply(skb);
>>> +
>>> +	trace_virtio_transport_alloc_pkt(src_cid, src_port,
>>> +					 dst_cid, dst_port,
>>> +					 payload_len,
>>> +					 info->type,
>>> +					 info->op,
>>> +					 info->flags);
>>> +
>>> +	return skb;
>>> +out:
>>> +	kfree_skb(skb);
>>> +	return NULL;
>>> +}
>>> +
>>>  /* This function can only be used on connecting/connected sockets,
>>>   * since a socket assigned to a transport is required.
>>>   *
>>> @@ -222,10 +335,12 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>>  static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>  					  struct virtio_vsock_pkt_info *info)
>>>  {
>>> +	u32 max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>>>  	u32 src_cid, src_port, dst_cid, dst_port;
>>>  	const struct virtio_transport *t_ops;
>>>  	struct virtio_vsock_sock *vvs;
>>>  	u32 pkt_len = info->pkt_len;
>>> +	bool can_zcopy = false;
>>>  	u32 rest_len;
>>>  	int ret;
>>>  
>>> @@ -254,15 +369,30 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>  	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
>>>  		return pkt_len;
>>>  
>>> +	if (info->msg) {
>>> +		/* If zerocopy is not enabled by 'setsockopt()', we behave as
>>> +		 * there is no MSG_ZEROCOPY flag set.
>>> +		 */
>>> +		if (!sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY))
>>> +			info->msg->msg_flags &= ~MSG_ZEROCOPY;
>>> +
>>> +		if (info->msg->msg_flags & MSG_ZEROCOPY)
>>> +			can_zcopy = virtio_transport_can_zcopy(info, pkt_len);
>>> +
>>> +		if (can_zcopy)
>>> +			max_skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE,
>>> +					    (MAX_SKB_FRAGS * PAGE_SIZE));
>>> +	}
>>> +
>>>  	rest_len = pkt_len;
>>>  
>>>  	do {
>>>  		struct sk_buff *skb;
>>>  		size_t skb_len;
>>>  
>>> -		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
>>> +		skb_len = min(max_skb_len, rest_len);
>>>  
>>> -		skb = virtio_transport_alloc_skb(info, skb_len,
>>> +		skb = virtio_transport_alloc_skb(vsk, info, skb_len, can_zcopy,
>>>  						 src_cid, src_port,
>>>  						 dst_cid, dst_port);
>>>  		if (!skb) {
>>> @@ -270,6 +400,17 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>  			break;
>>>  		}
>>>  
>>> +		/* This is last skb to send this portion of data. */
>>> +		if (info->msg && info->msg->msg_flags & MSG_ZEROCOPY &&
>>> +		    skb_len == rest_len && info->op == VIRTIO_VSOCK_OP_RW) {
>>> +			if (virtio_transport_init_zcopy_skb(vsk, skb,
>>> +							    info->msg,
>>> +							    can_zcopy)) {
>>> +				ret = -ENOMEM;
>>> +				break;
>>> +			}
>>> +		}
>>> +
>>>  		virtio_transport_inc_tx_pkt(vvs, skb);
>>>  
>>>  		ret = t_ops->send_pkt(skb);
>>> @@ -934,7 +1075,7 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
>>>  	if (!t)
>>>  		return -ENOTCONN;
>>>  
>>> -	reply = virtio_transport_alloc_skb(&info, 0,
>>> +	reply = virtio_transport_alloc_skb(NULL, &info, 0, false,
>>>  					   le64_to_cpu(hdr->dst_cid),
>>>  					   le32_to_cpu(hdr->dst_port),
>>>  					   le64_to_cpu(hdr->src_cid),
> 

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