Date:   Thu, 16 Feb 2023 17:15:20 +0000
From:   Bobby Eshleman <bobbyeshleman@gmail.com>
To:     Stefano Garzarella <sgarzare@redhat.com>
Cc:     Bobby Eshleman <bobby.eshleman@bytedance.com>, hdanton@sina.com,
        cong.wang@bytedance.com, kvm@vger.kernel.org,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        virtualization@lists.linux-foundation.org,
        Song Liu <song@kernel.org>, Eric Dumazet <edumazet@google.com>,
        Stanislav Fomichev <sdf@google.com>,
        linux-kselftest@vger.kernel.org, Shuah Khan <shuah@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>, jakub@cloudflare.com,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Yonghong Song <yhs@fb.com>, Paolo Abeni <pabeni@redhat.com>,
        KP Singh <kpsingh@kernel.org>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Jakub Kicinski <kuba@kernel.org>, Hao Luo <haoluo@google.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jiri Olsa <jolsa@kernel.org>, bpf@vger.kernel.org,
        Martin KaFai Lau <martin.lau@linux.dev>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH RFC net-next v2 1/3] vsock: support sockmap
Message-ID: <Y+5kqG1H+jX9WxFt@bullseye>
References: <20230118-support-vsock-sockmap-connectible-v2-0-58ffafde0965@bytedance.com>
 <20230118-support-vsock-sockmap-connectible-v2-1-58ffafde0965@bytedance.com>
 <20230216101110.fnwci5u5cwbkg2u5@sgarzare-redhat>
MIME-Version: 1.0
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In-Reply-To: <20230216101110.fnwci5u5cwbkg2u5@sgarzare-redhat>
Precedence: bulk

On Thu, Feb 16, 2023 at 11:11:10AM +0100, Stefano Garzarella wrote:
> On Mon, Jan 30, 2023 at 08:35:12PM -0800, Bobby Eshleman wrote:
> > This patch adds sockmap support for vsock sockets. It is intended to be
> > usable by all transports, but only the virtio transport is implemented.
> > 
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> > ---
> > drivers/vhost/vsock.c                   |   1 +
> > include/linux/virtio_vsock.h            |   1 +
> > include/net/af_vsock.h                  |  17 ++++
> > net/vmw_vsock/Makefile                  |   1 +
> > net/vmw_vsock/af_vsock.c                |  55 ++++++++--
> > net/vmw_vsock/virtio_transport.c        |   2 +
> > net/vmw_vsock/virtio_transport_common.c |  24 +++++
> > net/vmw_vsock/vsock_bpf.c               | 175 ++++++++++++++++++++++++++++++++
> > net/vmw_vsock/vsock_loopback.c          |   2 +
> > 9 files changed, 272 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index 1f3b89c885cc..3c6dc036b904 100644
> > --- a/drivers/vhost/vsock.c
> > +++ b/drivers/vhost/vsock.c
> > @@ -439,6 +439,7 @@ static struct virtio_transport vhost_transport = {
> > 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> > 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
> > 
> > +		.read_skb = virtio_transport_read_skb,
> > 	},
> > 
> > 	.send_pkt = vhost_transport_send_pkt,
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 3f9c16611306..c58453699ee9 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -245,4 +245,5 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 wanted);
> > void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
> > void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
> > int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
> > +int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
> > #endif /* _LINUX_VIRTIO_VSOCK_H */
> > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > index 568a87c5e0d0..a73f5fbd296a 100644
> > --- a/include/net/af_vsock.h
> > +++ b/include/net/af_vsock.h
> > @@ -75,6 +75,7 @@ struct vsock_sock {
> > 	void *trans;
> > };
> > 
> > +s64 vsock_connectible_has_data(struct vsock_sock *vsk);
> > s64 vsock_stream_has_data(struct vsock_sock *vsk);
> > s64 vsock_stream_has_space(struct vsock_sock *vsk);
> > struct sock *vsock_create_connected(struct sock *parent);
> > @@ -173,6 +174,9 @@ struct vsock_transport {
> > 
> > 	/* Addressing. */
> > 	u32 (*get_local_cid)(void);
> > +
> > +	/* Read a single skb */
> > +	int (*read_skb)(struct vsock_sock *, skb_read_actor_t);
> > };
> > 
> > /**** CORE ****/
> > @@ -225,5 +229,18 @@ int vsock_init_tap(void);
> > int vsock_add_tap(struct vsock_tap *vt);
> > int vsock_remove_tap(struct vsock_tap *vt);
> > void vsock_deliver_tap(struct sk_buff *build_skb(void *opaque), void *opaque);
> > +int vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> > +			      int flags);
> > +int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> > +			       size_t len, int flags);
> 
> checkpatch complains: "CHECK: Alignment should match open parenthesis"
> 
> > +
> > +#ifdef CONFIG_BPF_SYSCALL
> > +extern struct proto vsock_proto;
> > +int vsock_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);
> > +void __init vsock_bpf_build_proto(void);
> > +#else
> > +static inline void __init vsock_bpf_build_proto(void)
> > +{}
> > +#endif
> > 
> > #endif /* __AF_VSOCK_H__ */
> > diff --git a/net/vmw_vsock/Makefile b/net/vmw_vsock/Makefile
> > index 6a943ec95c4a..5da74c4a9f1d 100644
> > --- a/net/vmw_vsock/Makefile
> > +++ b/net/vmw_vsock/Makefile
> > @@ -8,6 +8,7 @@ obj-$(CONFIG_HYPERV_VSOCKETS) += hv_sock.o
> > obj-$(CONFIG_VSOCKETS_LOOPBACK) += vsock_loopback.o
> > 
> > vsock-y += af_vsock.o af_vsock_tap.o vsock_addr.o
> > +vsock-$(CONFIG_BPF_SYSCALL) += vsock_bpf.o
> > 
> > vsock_diag-y += diag.o
> > 
> > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > index 19aea7cba26e..f2cc04fb8b13 100644
> > --- a/net/vmw_vsock/af_vsock.c
> > +++ b/net/vmw_vsock/af_vsock.c
> > @@ -116,10 +116,13 @@ static void vsock_sk_destruct(struct sock *sk);
> > static int vsock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
> > 
> > /* Protocol family. */
> > -static struct proto vsock_proto = {
> > +struct proto vsock_proto = {
> > 	.name = "AF_VSOCK",
> > 	.owner = THIS_MODULE,
> > 	.obj_size = sizeof(struct vsock_sock),
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	.psock_update_sk_prot = vsock_bpf_update_proto,
> > +#endif
> > };
> > 
> > /* The default peer timeout indicates how long we will wait for a peer response
> > @@ -865,7 +868,7 @@ s64 vsock_stream_has_data(struct vsock_sock *vsk)
> > }
> > EXPORT_SYMBOL_GPL(vsock_stream_has_data);
> > 
> > -static s64 vsock_connectible_has_data(struct vsock_sock *vsk)
> > +s64 vsock_connectible_has_data(struct vsock_sock *vsk)
> > {
> > 	struct sock *sk = sk_vsock(vsk);
> > 
> > @@ -874,6 +877,7 @@ static s64 vsock_connectible_has_data(struct vsock_sock *vsk)
> > 	else
> > 		return vsock_stream_has_data(vsk);
> > }
> > +EXPORT_SYMBOL_GPL(vsock_connectible_has_data);
> > 
> > s64 vsock_stream_has_space(struct vsock_sock *vsk)
> > {
> > @@ -1131,6 +1135,13 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
> > 	return mask;
> > }
> > 
> > +static int vsock_read_skb(struct sock *sk, skb_read_actor_t read_actor)
> > +{
> > +	struct vsock_sock *vsk = vsock_sk(sk);
> > +
> > +	return vsk->transport->read_skb(vsk, read_actor);
> > +}
> > +
> > static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > 			       size_t len)
> > {
> > @@ -1241,19 +1252,34 @@ static int vsock_dgram_connect(struct socket *sock,
> > 
> > 	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> > 	sock->state = SS_CONNECTED;
> > +	sk->sk_state = TCP_ESTABLISHED;
> > 
> > out:
> > 	release_sock(sk);
> > 	return err;
> > }
> > 
> > -static int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> > -			       size_t len, int flags)
> > +int vsock_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> > +			size_t len, int flags)
> > {
> > -	struct vsock_sock *vsk = vsock_sk(sock->sk);
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	const struct proto *prot;
> > +#endif
> > +	struct vsock_sock *vsk;
> > +	struct sock *sk;
> > +
> > +	sk = sock->sk;
> > +	vsk = vsock_sk(sk);
> > +
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	prot = READ_ONCE(sk->sk_prot);
> > +	if (prot != &vsock_proto)
> > +		return prot->recvmsg(sk, msg, len, flags, NULL);
> > +#endif
> > 
> > 	return vsk->transport->dgram_dequeue(vsk, msg, len, flags);
> > }
> > +EXPORT_SYMBOL_GPL(vsock_dgram_recvmsg);
> > 
> > static const struct proto_ops vsock_dgram_ops = {
> > 	.family = PF_VSOCK,
> > @@ -1272,6 +1298,7 @@ static const struct proto_ops vsock_dgram_ops = {
> > 	.recvmsg = vsock_dgram_recvmsg,
> > 	.mmap = sock_no_mmap,
> > 	.sendpage = sock_no_sendpage,
> > +	.read_skb = vsock_read_skb,
> > };
> > 
> > static int vsock_transport_cancel_pkt(struct vsock_sock *vsk)
> > @@ -2086,13 +2113,16 @@ static int __vsock_seqpacket_recvmsg(struct sock *sk, struct msghdr *msg,
> > 	return err;
> > }
> > 
> > -static int
> > +int
> > vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> > 			  int flags)
> > {
> > 	struct sock *sk;
> > 	struct vsock_sock *vsk;
> > 	const struct vsock_transport *transport;
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	const struct proto *prot;
> > +#endif
> > 	int err;
> > 
> > 	sk = sock->sk;
> > @@ -2139,6 +2169,14 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> > 		goto out;
> > 	}
> > 
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	prot = READ_ONCE(sk->sk_prot);
> > +	if (prot != &vsock_proto) {
> > +		release_sock(sk);
> > +		return prot->recvmsg(sk, msg, len, flags, NULL);
> > +	}
> > +#endif
> > +
> > 	if (sk->sk_type == SOCK_STREAM)
> > 		err = __vsock_stream_recvmsg(sk, msg, len, flags);
> > 	else
> > @@ -2148,6 +2186,7 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> > 	release_sock(sk);
> > 	return err;
> > }
> > +EXPORT_SYMBOL_GPL(vsock_connectible_recvmsg);
> > 
> > static int vsock_set_rcvlowat(struct sock *sk, int val)
> > {
> > @@ -2188,6 +2227,7 @@ static const struct proto_ops vsock_stream_ops = {
> > 	.mmap = sock_no_mmap,
> > 	.sendpage = sock_no_sendpage,
> > 	.set_rcvlowat = vsock_set_rcvlowat,
> > +	.read_skb = vsock_read_skb,
> > };
> > 
> > static const struct proto_ops vsock_seqpacket_ops = {
> > @@ -2209,6 +2249,7 @@ static const struct proto_ops vsock_seqpacket_ops = {
> > 	.recvmsg = vsock_connectible_recvmsg,
> > 	.mmap = sock_no_mmap,
> > 	.sendpage = sock_no_sendpage,
> > +	.read_skb = vsock_read_skb,
> > };
> > 
> > static int vsock_create(struct net *net, struct socket *sock,
> > @@ -2348,6 +2389,8 @@ static int __init vsock_init(void)
> > 		goto err_unregister_proto;
> > 	}
> > 
> > +	vsock_bpf_build_proto();
> > +
> > 	return 0;
> > 
> > err_unregister_proto:
> > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > index 28b5a8e8e094..e95df847176b 100644
> > --- a/net/vmw_vsock/virtio_transport.c
> > +++ b/net/vmw_vsock/virtio_transport.c
> > @@ -457,6 +457,8 @@ static struct virtio_transport virtio_transport = {
> > 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> > 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> > 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
> > +
> > +		.read_skb = virtio_transport_read_skb,
> > 	},
> > 
> > 	.send_pkt = virtio_transport_send_pkt,
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index a1581c77cf84..82bdaf61ee02 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -1388,6 +1388,30 @@ int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *queue)
> > }
> > EXPORT_SYMBOL_GPL(virtio_transport_purge_skbs);
> > 
> > +int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_actor)
> > +{
> > +	struct virtio_vsock_sock *vvs = vsk->trans;
> > +	struct sock *sk = sk_vsock(vsk);
> > +	struct sk_buff *skb;
> > +	int off = 0;
> > +	int copied;
> > +	int err;
> > +
> > +	spin_lock_bh(&vvs->rx_lock);
> > +	/* Use __skb_recv_datagram() for race-free handling of the receive. It
> > +	 * works for types other than dgrams. */
> 
> Checkpatch:
>   WARNING: Block comments use a trailing */ on a separate line
> 
> Since we also use this convention in the other comments in this file,
> I would follow it.
> 
> > +	skb = __skb_recv_datagram(sk, &vvs->rx_queue, MSG_DONTWAIT, &off, &err);
> > +	spin_unlock_bh(&vvs->rx_lock);
> > +
> > +	if (!skb)
> > +		return err;
> > +
> > +	copied = recv_actor(sk, skb);
> > +	kfree_skb(skb);
> > +	return copied;
> > +}
> > +EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
> > +
> > MODULE_LICENSE("GPL v2");
> > MODULE_AUTHOR("Asias He");
> > MODULE_DESCRIPTION("common code for virtio vsock");
> > diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c
> > new file mode 100644
> > index 000000000000..ee92a1f42031
> > --- /dev/null
> > +++ b/net/vmw_vsock/vsock_bpf.c
> > @@ -0,0 +1,175 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2022 Bobby Eshleman <bobby.eshleman@bytedance.com>
> > + *
> > + * Based off of net/unix/unix_bpf.c
> > + */
> > +
> > +#include <linux/bpf.h>
> > +#include <linux/module.h>
> > +#include <linux/skmsg.h>
> > +#include <linux/socket.h>
> > +#include <linux/wait.h>
> > +#include <net/af_vsock.h>
> > +#include <net/sock.h>
> > +
> > +#define vsock_sk_has_data(__sk, __psock)				\
> > +		({	!skb_queue_empty(&__sk->sk_receive_queue) ||	\
> > +			!skb_queue_empty(&__psock->ingress_skb) ||	\
> > +			!list_empty(&__psock->ingress_msg);		\
> > +		})
> 
> Some suggestions from checkpatch that I would fix:
> 
> CHECK: Macro argument '__sk' may be better as '(__sk)' to avoid precedence issues
> CHECK: Macro argument '__psock' may be better as '(__psock)' to avoid precedence issues
> 
> > +
> > +static struct proto *vsock_prot_saved __read_mostly;
> > +static DEFINE_SPINLOCK(vsock_prot_lock);
> > +static struct proto vsock_bpf_prot;
> > +
> > +static bool vsock_has_data(struct sock *sk, struct sk_psock *psock)
> > +{
> > +	struct vsock_sock *vsk = vsock_sk(sk);
> > +	s64 ret;
> > +
> > +	ret = vsock_connectible_has_data(vsk);
> > +	if (ret > 0)
> > +		return true;
> > +
> > +	return vsock_sk_has_data(sk, psock);
> > +}
> > +
> > +static int vsock_msg_wait_data(struct sock *sk, struct sk_psock *psock, long timeo)
> 
> IIUC now this function returns 0 when there isn't data and 1 when there
> is data, maybe better to change the return type to bool.
> 
> > +{
> > +	int ret = 0;
> > +
> > +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
> > +
> > +	if (sk->sk_shutdown & RCV_SHUTDOWN)
> > +		return 1;
> > +
> > +	if (!timeo)
> > +		return ret;
> > +
> > +	add_wait_queue(sk_sleep(sk), &wait);
> > +	sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
> > +	ret = vsock_has_data(sk, psock);
> > +	if (!ret) {
> > +		wait_woken(&wait, TASK_INTERRUPTIBLE, timeo);
> > +		ret = vsock_has_data(sk, psock);
> > +	}
> > +	sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
> > +	remove_wait_queue(sk_sleep(sk), &wait);
> > +	return ret;
> > +}
> > +
> > +static int __vsock_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int flags)
> > +{
> > +	struct socket *sock = sk->sk_socket;
> > +	int err;
> > +
> > +	if (sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET)
> > +		err = vsock_connectible_recvmsg(sock, msg, len, flags);
> > +	else if (sk->sk_type == SOCK_DGRAM)
> > +		err = vsock_dgram_recvmsg(sock, msg, len, flags);
> > +	else
> > +		err = -EPROTOTYPE;
> > +
> > +	return err;
> > +}
> > +
> > +static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
> > +			     size_t len, int flags, int *addr_len)
> > +{
> > +	struct sk_psock *psock;
> > +	int copied;
> > +
> > +	psock = sk_psock_get(sk);
> > +	lock_sock(sk);
> > +	if (unlikely(!psock)) {
> > +		release_sock(sk);
> 
> I'm not sure we need the lock to check psock, so can we move this
> block before the lock_sock?
> 
> > +		return __vsock_recvmsg(sk, msg, len, flags);
> > +	}
> > +
> > +	if (vsock_has_data(sk, psock) && sk_psock_queue_empty(psock)) {
> > +		release_sock(sk);
> > +		sk_psock_put(sk, psock);
> > +		return __vsock_recvmsg(sk, msg, len, flags);
> > +	}
> > +
> > +msg_bytes_ready:
> 
> I saw that this code is also in unix_bpf.c and tcp_bpf.c, so I guess
> it's acceptable, but I would have avoided using a label to go back.
> I prefer a to use goto only for centralized exiting of functions.
> 
> One possible refactoring (not tested):
> 
>         copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
>         while (!copied) {
>                 long timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
> 
>                 if (!vsock_msg_wait_data(sk, psock, timeo)) {
>                         copied = -EAGAIN;
>                         break;
>                 }
> 
>                 if (sk_psock_queue_empty(psock)) {
>                         release_sock(sk);
>                         sk_psock_put(sk, psock);
>                         return __vsock_recvmsg(sk, msg, len, flags);
>                 }
> 
>                 copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
>         }
>         ...
> 
> I'm not sure why we need to call release_sock() and sk_psock_put()
> before __vsock_recvmsg(). If it is not needed we can simplify more the
> previous code.
> 
> The rest LGTM.
> 
> Thanks,
> Stefano
> 

Thanks Stefano, I'll incorporate your feedback in the next rev and
remove the RFC header as suggested.

Thanks again, hope you had a good time off work!

Best,
Bobby

> > +	copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
> > +	if (!copied) {
> > +		long timeo;
> > +		int data;
> > +
> > +		timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
> > +		data = vsock_msg_wait_data(sk, psock, timeo);
> > +		if (data) {
> > +			if (!sk_psock_queue_empty(psock))
> > +				goto msg_bytes_ready;
> > +			release_sock(sk);
> > +			sk_psock_put(sk, psock);
> > +			return __vsock_recvmsg(sk, msg, len, flags);
> > +		}
> > +		copied = -EAGAIN;
> > +	}
> > +	release_sock(sk);
> > +	sk_psock_put(sk, psock);
> > +
> > +	return copied;
> > +}
> > +
> > +/* Copy of original proto with updated sock_map methods */
> > +static struct proto vsock_bpf_prot = {
> > +	.close = sock_map_close,
> > +	.recvmsg = vsock_bpf_recvmsg,
> > +	.sock_is_readable = sk_msg_is_readable,
> > +	.unhash = sock_map_unhash,
> > +};
> > +
> > +static void vsock_bpf_rebuild_protos(struct proto *prot, const struct proto *base)
> > +{
> > +	*prot        = *base;
> > +	prot->close  = sock_map_close;
> > +	prot->recvmsg = vsock_bpf_recvmsg;
> > +	prot->sock_is_readable = sk_msg_is_readable;
> > +}
> > +
> > +static void vsock_bpf_check_needs_rebuild(struct proto *ops)
> > +{
> > +	/* Paired with the smp_store_release() below. */
> > +	if (unlikely(ops != smp_load_acquire(&vsock_prot_saved))) {
> > +		spin_lock_bh(&vsock_prot_lock);
> > +		if (likely(ops != vsock_prot_saved)) {
> > +			vsock_bpf_rebuild_protos(&vsock_bpf_prot, ops);
> > +			/* Make sure proto function pointers are updated before publishing the
> > +			 * pointer to the struct.
> > +			 */
> > +			smp_store_release(&vsock_prot_saved, ops);
> > +		}
> > +		spin_unlock_bh(&vsock_prot_lock);
> > +	}
> > +}
> > +
> > +int vsock_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)
> > +{
> > +	struct vsock_sock *vsk;
> > +
> > +	if (restore) {
> > +		sk->sk_write_space = psock->saved_write_space;
> > +		sock_replace_proto(sk, psock->sk_proto);
> > +		return 0;
> > +	}
> > +
> > +	vsk = vsock_sk(sk);
> > +	if (!vsk->transport)
> > +		return -ENODEV;
> > +
> > +	if (!vsk->transport->read_skb)
> > +		return -EOPNOTSUPP;
> > +
> > +	vsock_bpf_check_needs_rebuild(psock->sk_proto);
> > +	sock_replace_proto(sk, &vsock_bpf_prot);
> > +	return 0;
> > +}
> > +
> > +void __init vsock_bpf_build_proto(void)
> > +{
> > +	vsock_bpf_rebuild_protos(&vsock_bpf_prot, &vsock_proto);
> > +}
> > diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> > index 671e03240fc5..40753b661c13 100644
> > --- a/net/vmw_vsock/vsock_loopback.c
> > +++ b/net/vmw_vsock/vsock_loopback.c
> > @@ -94,6 +94,8 @@ static struct virtio_transport loopback_transport = {
> > 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> > 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> > 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
> > +
> > +		.read_skb = virtio_transport_read_skb,
> > 	},
> > 
> > 	.send_pkt = vsock_loopback_send_pkt,
> > 
> > -- 
> > 2.35.1
> > 
> 
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