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Message-ID: <rbyt6uomvimurmgchxpuyoqjehdleqzzohzzdnajgadrwkbwsf@qwlcvzqhqxqw>
Date: Mon, 26 Jun 2023 18:03:25 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc: Stefan Hajnoczi <stefanha@...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>, 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: [RFC PATCH v4 05/17] vsock/virtio: MSG_ZEROCOPY flag support
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@...rdevices.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?
> };
>
> 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
>
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