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Date: Fri, 28 Jul 2023 11:03:59 +0300
From: Arseniy Krasnov <avkrasnov@...rdevices.ru>
To: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella
<sgarzare@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
<pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang
<jasowang@...hat.com>, Bobby Eshleman <bobby.eshleman@...edance.com>
CC: <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<kernel@...rdevices.ru>, <oxffffaa@...il.com>
Subject: Re: [PATCH net-next v4 4/4] vsock/virtio: MSG_ZEROCOPY flag support
On 28.07.2023 01:26, 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@...rdevices.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.
> v3 -> v4:
> * 'msgzerocopy_check_iov' moved from 'struct vsock_transport' to
> 'struct virtio_transport' as it is virtio specific callback and
> never needed in other transports.
>
> include/linux/virtio_vsock.h | 5 +
> net/vmw_vsock/virtio_transport.c | 38 ++++
> net/vmw_vsock/virtio_transport_common.c | 257 ++++++++++++++++++------
> 3 files changed, 242 insertions(+), 58 deletions(-)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 17dbb7176e37..33d878abbfcb 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -160,6 +160,11 @@ struct virtio_transport {
>
> /* Takes ownership of the packet */
> int (*send_pkt)(struct sk_buff *skb);
> +
> + /* Used in MSG_ZEROCOPY mode. Checks that provided data
> + * could be transmitted with zerocopy mode.
> + */
> + bool (*msgzerocopy_check_iov)(const struct iov_iter *iov);
> };
>
> ssize_t
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 7bbcc8093e51..f0abcaad5cfd 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)
^^^
Oops, here is bug, it must be
if (min(iov_pages, MAX_SKB_FRAGS) + 1 <= vq->num_max)
This is because whole iov is not inserted to the tx queue. iov is splitted by
MAX_SKB_FRAGS limit (in tx loop in virtio_transport_common.c) and then every
skb is inserted to the tx queue. I'll fix it in v5, sorry
Thanks, Arseniy
> + res = true;
> + }
> +
> + rcu_read_unlock();
> +
> + return res;
> +}
> +
> static bool virtio_transport_seqpacket_allow(u32 remote_cid);
>
> static struct virtio_transport virtio_transport = {
> @@ -491,6 +528,7 @@ static struct virtio_transport virtio_transport = {
> },
>
> .send_pkt = virtio_transport_send_pkt,
> + .msgzerocopy_check_iov = virtio_transport_msgzerocopy_check_iov,
> };
>
> static bool virtio_transport_seqpacket_allow(u32 remote_cid)
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index de7b44675254..659f9d70266b 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 virtio_transport *t_ops;
> + 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_ops = virtio_transport_get_ops(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_ops->msgzerocopy_check_iov &&
> + !t_ops->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);
> @@ -985,7 +1126,7 @@ 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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