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    SubjectRe: [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@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) {
    >> + 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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