Stefano Garzarella
2023-Jul-25 08:43 UTC
[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 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) > >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), >