Message-ID: <2k3cbz762ua3fmlben5vcm7rs624sktaltbz3ldeevwiguwk2w@klggxj5e3ueu>
Date:   Tue, 25 Jul 2023 10:43:54 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <avkrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...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 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.

I think so.
So, should we check also that here?

>
>Thanks, Arseniy
>
>> +			res = true;
>> +	}
>> +
>> +	rcu_read_unlock();
>> +
>> +	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;

I'd avoid adding a new transport callback used only internally in virtio
transports.

Usually the transport callbacks are used in af_vsock.c, if we need a
callback just for virtio transports, maybe better to add it in struct
virtio_vsock_pkt_info or struct virtio_vsock_sock.

Maybe better the last one so we don't have to allocate pointer space
for each packet and you should reach it via info.

Thanks,
Stefano

>>
>> -			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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