Michael S. Tsirkin
2023-Jul-25 13:22 UTC
[PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support
On Tue, Jul 25, 2023 at 04:04:13PM +0300, Arseniy Krasnov wrote:> > > On 25.07.2023 14:50, Michael S. Tsirkin 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 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. > >> > >> Thanks, Arseniy > > > > Actually the reverse. With indirect you are limited to num_max. > > Without you are limited to whatever space is left in the > > queue (which you did not check here, so you should). > > I mean that with indirect, we only need one buffer, and we can just wait > for enough space - for this single buffer ( as we discussed a little bit before). > But if indirect buffer is not supported - we need that whole packet must fit > to the size of tx queue - otherwise it never be transmitted. > > Thanks, Arseniyyes but according to virtio spec it's illegal to add s/g that is bigger than queue size.> > > > > >>> + res = true; > >>> + } > >>> + > >>> + rcu_read_unlock(); > > > > Just curious: > > is the point of all this RCU dance to allow vsock > > to change from under us? then why is it ok to > > have it change? the virtio_transport_msgzerocopy_check_iov > > will then refer to the old vsock ... > > > > > >>> + > >>> + 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), > >