[RFC,v4,05/17] vsock/virtio: MSG_ZEROCOPY flag support

  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(-)
  

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?

> 	};
>
> 	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
>
  

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.

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
>>
>
  

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
  

On 27.06.2023 10:50, Stefano Garzarella wrote:
> 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?

Sure! here is what happens: difference between these functions is that 'skb_set_owner_w()'
sets another destructor - 'sock_wfree()':

https://elixir.bootlin.com/linux/v6.4/source/net/core/sock.c#L2408

This destructor also updates 'sk->sk_wmem_alloc' during skb freeing. Why this is needed?
Because '__zerocopy_sg_from_iter()' updates 'sk_wmem_alloc' if socket is NOT SOCK_STREAM
or socket was NOT passed as input argument (it is not obvious why, but it is so):

https://elixir.bootlin.com/linux/latest/source/net/core/datagram.c#L646

So to support both types of sockets (seqpacket and stream) I decided to try pass NULL always
as socket argument to '__zerocopy_sg_from_iter()', with this 'sk_wmem_alloc' will be always
updated in '__zerocopy_sg_from_iter()' and then we decrease 'sk_wmem_alloc' in 'sock_wfree()'.

May be this looks strange - I tried to understand logic of this code in '__zerocopy_sg_from_iter()',
but it requires more deep analysis. Anyway it works:)

Thanks, Arseniy

> 
> 
> Thanks,
> Stefano
>
  

On Tue, Jun 27, 2023 at 11:22:52AM +0300, Arseniy Krasnov wrote:
>
>
>On 27.06.2023 10:50, Stefano Garzarella wrote:
>> 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?
>
>Sure! here is what happens: difference between these functions is that 'skb_set_owner_w()'
>sets another destructor - 'sock_wfree()':
>
>https://elixir.bootlin.com/linux/v6.4/source/net/core/sock.c#L2408
>
>This destructor also updates 'sk->sk_wmem_alloc' during skb freeing. Why this is needed?
>Because '__zerocopy_sg_from_iter()' updates 'sk_wmem_alloc' if socket is NOT SOCK_STREAM
>or socket was NOT passed as input argument (it is not obvious why, but it is so):
>
>https://elixir.bootlin.com/linux/latest/source/net/core/datagram.c#L646
>
>So to support both types of sockets (seqpacket and stream) I decided to try pass NULL always
>as socket argument to '__zerocopy_sg_from_iter()', with this 'sk_wmem_alloc' will be always
>updated in '__zerocopy_sg_from_iter()' and then we decrease 'sk_wmem_alloc' in 'sock_wfree()'.
>
>May be this looks strange - I tried to understand logic of this code in '__zerocopy_sg_from_iter()',
>but it requires more deep analysis. Anyway it works:)

Yep, it should require also more analysis on my side :-)

Please document it in the commit description, so if we will find any
issue in the future, we know why we did this change.

Thanks,
Stefano