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Date:   Tue, 25 Jul 2023 14:28:02 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <avkrasnov@sberdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support
Message-ID: <o6axh6mxd6mxai2zrpax6wa25slns7ysz5xsegntskvfxl53mt@wowjgb3jazt6>
References: <20230720214245.457298-1-AVKrasnov@sberdevices.ru>
 <20230720214245.457298-5-AVKrasnov@sberdevices.ru>
 <091c067b-43a0-da7f-265f-30c8c7e62977@sberdevices.ru>
 <2k3cbz762ua3fmlben5vcm7rs624sktaltbz3ldeevwiguwk2w@klggxj5e3ueu>
 <51022d5f-5b50-b943-ad92-b06f60bef433@sberdevices.ru>
 <3d1d76c9-2fdb-3dfe-222a-b2184cf17708@sberdevices.ru>
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In-Reply-To: <3d1d76c9-2fdb-3dfe-222a-b2184cf17708@sberdevices.ru>
Precedence: bulk

On Tue, Jul 25, 2023 at 12:16:11PM +0300, Arseniy Krasnov wrote:
>
>
>On 25.07.2023 11:46, Arseniy Krasnov wrote:
>>
>>
>> On 25.07.2023 11:43, Stefano Garzarella 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@sberdevices.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) {

Just noted, what about the following to reduce the indentation?

         if (!vsock) {
             goto out;
         }
             ...
             ...
     out:
         rcu_read_unlock();
         return res;

>>>>> +??????? 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.
>>
>> Ok, I see.
>>
>>>
>>> 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.
>
>Hm, may be I just need to move this callback from 'struct vsock_transport' to parent 'struct virtio_transport',
>after 'send_pkt' callback. In this case:
>1) AF_VSOCK part is not touched.
>2) This callback stays in 'virtio_transport.c' and is set also in this file.
>   vhost and loopback are unchanged - only 'send_pkt' still enabled in both
>   files for these two transports.

Yep, this could also work!

Stefano

>
>Thanks, Arseniy
>
>>>
>>> Maybe better the last one so we don't have to allocate pointer space
>>> for each packet and you should reach it via info.
>>
>> Ok, thanks, I'll try this way
>>
>> Thanks, Arseniy
>>
>>>
>>> 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),
>>>>
>>>
>