On Sat, Jul 01, 2023 at 09:39:35AM +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()'. 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:
v4 -> v5:
* Remove unused 'vsk' arg from 'virtio_transport_fill_linear_skb()'.
* Remove old comment 'Returns a new packet on success...'.
* Commit message update by adding details why this patch uses
'skb_set_owner_w()' instead of previous 'skb_set_owner_sk_safe()'.
* 'hdr' variable declaration and assignment in a single line.
* Rename 'max_skb_cap' to 'max_skb_len'.
* Use 'info->msg->msg_flags' to check MSG_ZEROCOPY flag instead of
field 'flags' of struct 'virtio_vsock_pkt_info'. This was a bug.
net/vmw_vsock/virtio_transport_common.c | 262 ++++++++++++++++++------
1 file changed, 200 insertions(+), 62 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index dfc48b56d0a2..2269530ea737 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -37,27 +37,99 @@ 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);
+
We can remove this extra blank line.
+ 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 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 +140,6 @@ 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(const struct sk_buff *skb,
@@ -214,6 +250,79 @@ 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 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));
+
+ 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, info, payload_len);
What about renaming that function in virtio_transport_fill_skb()
and hide this block there?
+ }
+
+ if (err)
+ goto out;
+
+ VIRTIO_VSOCK_SKB_CB(skb)->frag_off = 0;
Why we need this initialization?
Should all the `cb` fields already initialized to 0?
+
+ 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.
*
@@ -226,6 +335,8 @@ 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_len;
u32 rest_len;
int ret;
@@ -254,22 +365,49 @@ 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 (info->msg && !sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY))
+ info->msg->msg_flags &= ~MSG_ZEROCOPY;
+
+ if (info->msg && 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));
+ else
+ max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
+
IIUC, all these checks only make sense if `info->msg` is true, right?
If it is the case, I would refactor in this way (not tested):
u32 max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
bool can_zcopy = false;
if (info->msg) {
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,
- 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->msg &&
+ info->msg->msg_flags & MSG_ZEROCOPY &&
I would move `info->msg->msg_flags & MSG_ZEROCOPY` on top to make it
more readable and understand that this is only for zero-copy.
(of course checking before `info->msg`)
+ 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);
@@ -939,11 +1077,11 @@ 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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