Re: [PATCH net-next v3 4/4] vsock/virtio: MSG_ZEROCOPY flag support
From: Arseniy Krasnov
Date: Tue Jul 25 2023 - 05:22:43 EST
On 25.07.2023 11:46, Arseniy Krasnov wrote:
>
>
> On 25.07.2023 11:43, Stefano Garzarella 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.
>>
>> 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.
>
> Ok, I see.
>
>>
>> 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.
Hm, may be I just need to move this callback from 'struct vsock_transport' to parent 'struct virtio_transport',
after 'send_pkt' callback. In this case:
1) AF_VSOCK part is not touched.
2) This callback stays in 'virtio_transport.c' and is set also in this file.
vhost and loopback are unchanged - only 'send_pkt' still enabled in both
files for these two transports.
Thanks, Arseniy
>>
>> Maybe better the last one so we don't have to allocate pointer space
>> for each packet and you should reach it via info.
>
> Ok, thanks, I'll try this way
>
> Thanks, Arseniy
>
>>
>> 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),
>>>
>>