netdev - Re: [PATCH net-next v7] virtio/vsock: replace virtio_vsock_pkt with sk

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Message-ID: <4b66f91f23a3eb91c3232bc68f45bdb799217c40.camel@redhat.com>
Date:   Wed, 14 Dec 2022 11:58:47 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Bobby Eshleman <bobby.eshleman@...edance.com>
Cc:     Bobby Eshleman <bobbyeshleman@...il.com>,
        Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Krasnov Arseniy <oxffffaa@...il.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v7] virtio/vsock: replace virtio_vsock_pkt with
 sk_buff

On Tue, 2022-12-13 at 19:28 +0000, Bobby Eshleman wrote:
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 5703775af129..2a5994b029b2 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -51,8 +51,7 @@ struct vhost_vsock {
>  	struct hlist_node hash;
>  
>  	struct vhost_work send_pkt_work;
> -	spinlock_t send_pkt_list_lock;
> -	struct list_head send_pkt_list;	/* host->guest pending packets */
> +	struct sk_buff_head send_pkt_queue; /* host->guest pending packets */
>  
>  	atomic_t queued_replies;
>  
> @@ -108,40 +107,33 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>  	vhost_disable_notify(&vsock->dev, vq);
>  
>  	do {
> -		struct virtio_vsock_pkt *pkt;
> +		struct virtio_vsock_hdr *hdr;
> +		size_t iov_len, payload_len;
>  		struct iov_iter iov_iter;
> +		u32 flags_to_restore = 0;
> +		struct sk_buff *skb;
>  		unsigned out, in;
>  		size_t nbytes;
> -		size_t iov_len, payload_len;
>  		int head;
> -		u32 flags_to_restore = 0;
>  
> -		spin_lock_bh(&vsock->send_pkt_list_lock);
> -		if (list_empty(&vsock->send_pkt_list)) {
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +		spin_lock(&vsock->send_pkt_queue.lock);
> +		skb = __skb_dequeue(&vsock->send_pkt_queue);
> +		spin_unlock(&vsock->send_pkt_queue.lock);

Here you use a plain spin_lock(), but every other lock has the _bh()
variant. A few lines above this functions acquires a mutex, so this is
process context (and not BH context): I guess you should use _bh()
here, too.

[...]

> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 35d7eedb5e8e..0385df976d41 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -3,10 +3,116 @@
>  #define _LINUX_VIRTIO_VSOCK_H
>  
>  #include <uapi/linux/virtio_vsock.h>
> +#include <linux/bits.h>
>  #include <linux/socket.h>
>  #include <net/sock.h>
>  #include <net/af_vsock.h>
>  
> +#define VIRTIO_VSOCK_SKB_HEADROOM (sizeof(struct virtio_vsock_hdr))
> +
> +enum virtio_vsock_skb_flags {
> +	VIRTIO_VSOCK_SKB_FLAGS_REPLY		= BIT(0),
> +	VIRTIO_VSOCK_SKB_FLAGS_TAP_DELIVERED	= BIT(1),
> +};

It looks like the above enum is not used anymore, you can drop it.

[...]

> @@ -121,20 +108,18 @@ static void vsock_loopback_work(struct work_struct *work)
>  {
>  	struct vsock_loopback *vsock =
>  		container_of(work, struct vsock_loopback, pkt_work);
> -	LIST_HEAD(pkts);
> +	struct sk_buff_head pkts;
> +	struct sk_buff *skb;
> +
> +	skb_queue_head_init(&pkts);
>  
>  	spin_lock_bh(&vsock->pkt_list_lock);
> -	list_splice_init(&vsock->pkt_list, &pkts);
> +	skb_queue_splice_init(&vsock->pkt_queue, &pkts);
>  	spin_unlock_bh(&vsock->pkt_list_lock);
>  
> -	while (!list_empty(&pkts)) {
> -		struct virtio_vsock_pkt *pkt;
> -
> -		pkt = list_first_entry(&pkts, struct virtio_vsock_pkt, list);
> -		list_del_init(&pkt->list);
> -
> -		virtio_transport_deliver_tap_pkt(pkt);
> -		virtio_transport_recv_pkt(&loopback_transport, pkt);
> +	while ((skb = skb_dequeue(&pkts))) {

Minor nit: since this code has complete ownership of the pkts queue,
you can use the lockless dequeue variant here:

	while ((skb = __skb_dequeue(&pkts))) {

> +		virtio_transport_deliver_tap_pkt(skb);
> +		virtio_transport_recv_pkt(&loopback_transport, skb);
>  	}
>  }
>  

Other then that LGTM. @Michael: feel free to take this via your tree,
once that the above feedback has been addressed, thanks!

Paolo