Michael S. Tsirkin
2023-Jul-25 08:25 UTC
[PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support
On Fri, Jul 21, 2023 at 12:42:45AM +0300, 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 at 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) > + res = true;Yes but can't there already be buffers in the queue? Then you can't stick num_max there.> + } > + > + 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; > > - 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), > -- > 2.25.1