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Date:   Tue, 27 Jun 2023 09:50:50 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <avkrasnov@sberdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [RFC PATCH v4 05/17] vsock/virtio: MSG_ZEROCOPY flag support
Message-ID: <m5q3fqqvur4pcvkcxx36ivoqu77tsrjd4xna6zszmzq34dbqq5@6wfrhllk6tsq>
References: <20230603204939.1598818-1-AVKrasnov@sberdevices.ru>
 <20230603204939.1598818-6-AVKrasnov@sberdevices.ru>
 <rbyt6uomvimurmgchxpuyoqjehdleqzzohzzdnajgadrwkbwsf@qwlcvzqhqxqw>
 <b25f0c4d-828c-ffe8-2780-2c954ed8770a@sberdevices.ru>
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In-Reply-To: <b25f0c4d-828c-ffe8-2780-2c954ed8770a@sberdevices.ru>
Precedence: bulk

On Tue, Jun 27, 2023 at 07:41:51AM +0300, Arseniy Krasnov wrote:
>
>
>On 26.06.2023 19:03, Stefano Garzarella wrote:
>> On Sat, Jun 03, 2023 at 11:49:27PM +0300, Arseniy Krasnov wrote:
>>> This adds handling of MSG_ZEROCOPY flag on transmission path: if this
>>> flag is set and zerocopy transmission is possible, 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()'.
>>>
>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>>> ---
>>> net/vmw_vsock/virtio_transport_common.c | 270 ++++++++++++++++++------
>>> 1 file changed, 208 insertions(+), 62 deletions(-)
>>>
>>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>>> index 0de562c1dc4b..f1ec38c72db7 100644
>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>> @@ -37,27 +37,100 @@ 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;
>>> +static bool virtio_transport_can_zcopy(struct virtio_vsock_pkt_info *info,
>>> +?????????????????????? size_t max_to_send)
>>> +{
>>> +??? struct iov_iter *iov_iter;
>>> +
>>> +??? if (!info->msg)
>>> +??????? return false;
>>> +
>>> +??? iov_iter = &info->msg->msg_iter;
>>> +
>>> +??? /* 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;
>>> +??? }
>>> +
>>> +??? skb_zcopy_init(skb, uarg);
>>> +
>>> +??? return 0;
>>> +}
>>> +
>>> +static int virtio_transport_fill_linear_skb(struct sk_buff *skb,
>>> +??????????????????????? struct vsock_sock *vsk,
>>
>> `vsk` seems unused
>>
>>> +??????????????????????? struct virtio_vsock_pkt_info *info,
>>> +??????????????????????? size_t len)
>>> +{
>>> ????void *payload;
>>> ????int err;
>>>
>>> -??? skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>>> -??? if (!skb)
>>> -??????? return NULL;
>>> +??? 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;
>>> +}
>>> +
>>> +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;
>>>
>>> ????hdr = virtio_vsock_hdr(skb);
>>> ????hdr->type??? = cpu_to_le16(info->type);
>>> @@ -68,42 +141,6 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
>>> ????hdr->dst_port??? = cpu_to_le32(dst_port);
>>> ????hdr->flags??? = cpu_to_le32(info->flags);
>>> ????hdr->len??? = cpu_to_le32(len);
>>> -
>>> -??? if (info->msg && len > 0) {
>>> -??????? payload = skb_put(skb, len);
>>> -??????? err = memcpy_from_msg(payload, info->msg, len);
>>> -??????? if (err)
>>> -??????????? goto out;
>>> -
>>> -??????? if (msg_data_left(info->msg) == 0 &&
>>> -??????????? info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
>>> -??????????? 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,
>>> -???????????????????? len,
>>> -???????????????????? info->type,
>>> -???????????????????? info->op,
>>> -???????????????????? info->flags);
>>> -
>>> -??? 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;
>>> -??? }
>>> -
>>> -??? return skb;
>>> -
>>> -out:
>>> -??? kfree_skb(skb);
>>> -??? return NULL;
>>> }
>>>
>>> static void virtio_transport_copy_nonlinear_skb(struct sk_buff *skb,
>>> @@ -214,6 +251,85 @@ static u16 virtio_transport_get_type(struct sock *sk)
>>> ??????? return VIRTIO_VSOCK_TYPE_SEQPACKET;
>>> }
>>>
>>> +/* Returns a new packet on success, otherwise returns NULL.
>>> + *
>>> + * If NULL is returned, errp is set to a negative errno.
>>
>> I had noticed this in Bobby's patches, I think it's an old comment we
>> left around.
>>
>>> + */
>>> +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 dst_cid,
>>> +????????????????????????? u32 dst_port,
>>> +????????????????????????? u32 src_cid,
>>> +????????????????????????? u32 src_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));
>>
>> why we are moving from skb_set_owner_sk_safe() to skb_set_owner_w()?
>>
>> We should mention this in the commit description.
>>
>>> +
>>> +??? if (info->msg && payload_len > 0) {
>>> +??????? int err;
>>> +
>>> +??????? if (zcopy) {
>>> +??????????? err = __zerocopy_sg_from_iter(info->msg, NULL, skb,
>>> +????????????????????????????? &info->msg->msg_iter,
>>> +????????????????????????????? payload_len);
>>> +??????? } else {
>>> +??????????? err = virtio_transport_fill_linear_skb(skb, vsk, info, payload_len);
>>> +??????? }
>>> +
>>> +??????? if (err)
>>> +??????????? goto out;
>>> +
>>> +??????? VIRTIO_VSOCK_SKB_CB(skb)->frag_off = 0;
>>> +
>>> +??????? if (info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
>>> +??????????? struct virtio_vsock_hdr *hdr;
>>> +
>>> +??????????? hdr = virtio_vsock_hdr(skb);
>>
>> Just `struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);` should be
>> fine.
>>
>>> +
>>> +??????????? 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.
>>> ?*
>>> @@ -226,6 +342,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>> ????const struct virtio_transport *t_ops;
>>> ????struct virtio_vsock_sock *vvs;
>>> ????u32 pkt_len = info->pkt_len;
>>> +??? bool can_zcopy = false;
>>> +??? u32 max_skb_cap;
>>> ????u32 rest_len;
>>> ????int ret;
>>>
>>> @@ -254,22 +372,49 @@ 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 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->flags &= ~MSG_ZEROCOPY;
>>> +
>>> +??? if (info->flags & MSG_ZEROCOPY)
>>> +??????? can_zcopy = virtio_transport_can_zcopy(info, pkt_len);
>>> +
>>> +??? if (can_zcopy)
>>> +??????? max_skb_cap = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE,
>>> +??????????????????? (MAX_SKB_FRAGS * PAGE_SIZE));
>>> +??? else
>>> +??????? max_skb_cap = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>>> +
>>
>> We use `len` very often, what about `max_skb_len`?
>>
>>> ????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_cap, rest_len);
>>>
>>> -??????? skb = virtio_transport_alloc_skb(info, skb_len,
>>> -???????????????????????? src_cid, src_port,
>>> -???????????????????????? dst_cid, dst_port);
>>> +??????? skb = virtio_transport_alloc_skb(vsk, info, skb_len, can_zcopy,
>>> +???????????????????????? dst_cid, dst_port,
>>> +???????????????????????? src_cid, src_port);
>>> ??????? if (!skb) {
>>> ??????????? ret = -ENOMEM;
>>> ??????????? break;
>>> ??????? }
>>>
>>> +??????? /* This is last skb to send this portion of data. */
>>> +??????? if (skb_len == rest_len &&
>>> +??????????? info->flags & MSG_ZEROCOPY &&
>>> +??????????? 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);
>>> @@ -884,6 +1029,7 @@ virtio_transport_stream_enqueue(struct vsock_sock *vsk,
>>> ??????? .msg = msg,
>>> ??????? .pkt_len = len,
>>> ??????? .vsk = vsk,
>>> +??????? .flags = msg->msg_flags,
>>
>> These flags then get copied into the virtio_vsock_hdr, which I don't
>> think is a good idea.
>>
>> Why not using directly info->msg->msg_flags?
>
>Ops, yes, it's a bug, You're right, this is really wrong as there are two different
>sets of flags - MSG_XXX passed to syscall and flags in the header of packet.

Yep.

What about the moving from skb_set_owner_sk_safe() to skb_set_owner_w()?
Was it voluntary? If so, can you explain why?


Thanks,
Stefano