Re: [PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support
From: Arseniy Krasnov
Date: Tue Jul 25 2023 - 09:10:08 EST
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@xxxxxxxxxxxxxx>
>>> ---
>>> 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, Arseniy
>
>
>>> + 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),
>