Re: [RFC PATCH v4 05/17] vsock/virtio: MSG_ZEROCOPY flag support
From: Arseniy Krasnov
Date: Tue Jun 27 2023 - 00:48:15 EST
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@xxxxxxxxxxxxxx>
>> ---
>> 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.
Thanks, Arseniy
>
>> };
>>
>> return virtio_transport_send_pkt_info(vsk, &info);
>> @@ -935,11 +1081,11 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
>> if (!t)
>> return -ENOTCONN;
>>
>> - reply = virtio_transport_alloc_skb(&info, 0,
>> - le64_to_cpu(hdr->dst_cid),
>> - le32_to_cpu(hdr->dst_port),
>> + reply = virtio_transport_alloc_skb(NULL, &info, 0, false,
>> le64_to_cpu(hdr->src_cid),
>> - le32_to_cpu(hdr->src_port));
>> + le32_to_cpu(hdr->src_port),
>> + le64_to_cpu(hdr->dst_cid),
>> + le32_to_cpu(hdr->dst_port));
>> if (!reply)
>> return -ENOMEM;
>>
>> --
>> 2.25.1
>>
>