[PATCH RFC net-next v5 03/14] af_vsock: support multi-transport datagrams

Bobby Eshleman
2023-07-19T00:50:17Z

This patch adds support for multi-transport datagrams.

This includes:
- Per-packet lookup of transports when using sendto(sockaddr_vm)
- Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
sockaddr_vm
- rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
- connect() now assigns the transport for (similar to connectible
sockets)

To preserve backwards compatibility with VMCI, some important changes
are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
be used for dgrams only if there is not yet a g2h or h2g transport that
has been registered that can transmit the packet. If there is a g2h/h2g
transport for that remote address, then that transport will be used and
not "transport_dgram". This essentially makes "transport_dgram" a
fallback transport for when h2g/g2h has not yet gone online, and so it
is renamed "transport_dgram_fallback". VMCI implements this transport.

The logic around "transport_dgram" needs to be retained to prevent
breaking VMCI:

1) VMCI datagrams existed prior to h2g/g2h and so operate under a
different paradigm. When the vmci transport comes online, it registers
itself with the DGRAM feature, but not H2G/G2H. Only later when the
transport has more information about its environment does it register
H2G or G2H. In the case that a datagram socket is created after
VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
the "transport_dgram" transport is the only registered transport and so
needs to be used.

2) VMCI seems to require a special message be sent by the transport when a
datagram socket calls bind(). Under the h2g/g2h model, the transport
is selected using the remote_addr which is set by connect(). At
bind time there is no remote_addr because often no connect() has been
called yet: the transport is null. Therefore, with a null transport
there doesn't seem to be any good way for a datagram socket to tell the
VMCI transport that it has just had bind() called upon it.

With the new fallback logic, after H2G/G2H comes online the socket layer
will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
coming online, the socket layer will access the VMCI transport via
"transport_dgram_fallback".

Only transports with a special datagram fallback use-case such as VMCI
need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.

Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
---
drivers/vhost/vsock.c | 1 -
include/linux/virtio_vsock.h | 2 --
include/net/af_vsock.h | 10 +++---
net/vmw_vsock/af_vsock.c | 64 ++++++++++++++++++++++++++-------
net/vmw_vsock/hyperv_transport.c | 6 ----
net/vmw_vsock/virtio_transport.c | 1 -
net/vmw_vsock/virtio_transport_common.c | 7 ----
net/vmw_vsock/vmci_transport.c | 2 +-
net/vmw_vsock/vsock_loopback.c | 1 -
9 files changed, 58 insertions(+), 36 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ae8891598a48..d5d6a3c3f273 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
.cancel_pkt = vhost_transport_cancel_pkt,

.dgram_enqueue = virtio_transport_dgram_enqueue,
- .dgram_bind = virtio_transport_dgram_bind,
.dgram_allow = virtio_transport_dgram_allow,

.stream_enqueue = virtio_transport_stream_enqueue,
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 18cbe8d37fca..7632552bee58 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
bool virtio_transport_stream_allow(u32 cid, u32 port);
-int virtio_transport_dgram_bind(struct vsock_sock *vsk,
- struct sockaddr_vm *addr);
bool virtio_transport_dgram_allow(u32 cid, u32 port);

int virtio_transport_connect(struct vsock_sock *vsk);
diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 305d57502e89..f6a0ca9d7c3e 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {

/* Transport features flags */
/* Transport provides host->guest communication */
-#define VSOCK_TRANSPORT_F_H2G 0x00000001
+#define VSOCK_TRANSPORT_F_H2G 0x00000001
/* Transport provides guest->host communication */
-#define VSOCK_TRANSPORT_F_G2H 0x00000002
-/* Transport provides DGRAM communication */
-#define VSOCK_TRANSPORT_F_DGRAM 0x00000004
+#define VSOCK_TRANSPORT_F_G2H 0x00000002
+/* Transport provides fallback for DGRAM communication */
+#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK 0x00000004
/* Transport provides local (loopback) communication */
-#define VSOCK_TRANSPORT_F_LOCAL 0x00000008
+#define VSOCK_TRANSPORT_F_LOCAL 0x00000008

struct vsock_transport {
struct module *module;
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index ae5ac5531d96..26c97b33d55a 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -139,8 +139,8 @@ struct proto vsock_proto = {
static const struct vsock_transport *transport_h2g;
/* Transport used for guest->host communication */
static const struct vsock_transport *transport_g2h;
-/* Transport used for DGRAM communication */
-static const struct vsock_transport *transport_dgram;
+/* Transport used as a fallback for DGRAM communication */
+static const struct vsock_transport *transport_dgram_fallback;
/* Transport used for local communication */
static const struct vsock_transport *transport_local;
static DEFINE_MUTEX(vsock_register_mutex);
@@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
return transport;
}

+static const struct vsock_transport *
+vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
+{
+ const struct vsock_transport *transport;
+
+ transport = vsock_connectible_lookup_transport(cid, flags);
+ if (transport)
+ return transport;
+
+ return transport_dgram_fallback;
+}
+
/* Assign a transport to a socket and call the .init transport callback.
*
* Note: for connection oriented socket this must be called when vsk->remote_addr
@@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)

switch (sk->sk_type) {
case SOCK_DGRAM:
- new_transport = transport_dgram;
+ new_transport = vsock_dgram_lookup_transport(remote_cid,
+ remote_flags);
break;
case SOCK_STREAM:
case SOCK_SEQPACKET:
@@ -692,6 +705,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
static int __vsock_bind_dgram(struct vsock_sock *vsk,
struct sockaddr_vm *addr)
{
+ if (!vsk->transport || !vsk->transport->dgram_bind)
+ return -EINVAL;
+
return vsk->transport->dgram_bind(vsk, addr);
}

@@ -1162,6 +1178,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
struct vsock_sock *vsk;
struct sockaddr_vm *remote_addr;
const struct vsock_transport *transport;
+ bool module_got = false;

if (msg->msg_flags & MSG_OOB)
return -EOPNOTSUPP;
@@ -1173,19 +1190,34 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,

lock_sock(sk);

- transport = vsk->transport;
-
err = vsock_auto_bind(vsk);
if (err)
goto out;

-
/* If the provided message contains an address, use that. Otherwise
* fall back on the socket's remote handle (if it has been connected).
*/
if (msg->msg_name &&
vsock_addr_cast(msg->msg_name, msg->msg_namelen,
&remote_addr) == 0) {
+ transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
+ remote_addr->svm_flags);
+ if (!transport) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ if (!try_module_get(transport->module)) {
+ err = -ENODEV;
+ goto out;
+ }
+
+ /* When looking up a transport dynamically and acquiring a
+ * reference on the module, we need to remember to release the
+ * reference later.
+ */
+ module_got = true;
+
/* Ensure this address is of the right type and is a valid
* destination.
*/
@@ -1200,6 +1232,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
} else if (sock->state == SS_CONNECTED) {
remote_addr = &vsk->remote_addr;

+ transport = vsk->transport;
if (remote_addr->svm_cid == VMADDR_CID_ANY)
remote_addr->svm_cid = transport->get_local_cid();

@@ -1224,6 +1257,8 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
err = transport->dgram_enqueue(vsk, remote_addr, msg, len);

out:
+ if (module_got)
+ module_put(transport->module);
release_sock(sk);
return err;
}
@@ -1256,13 +1291,18 @@ static int vsock_dgram_connect(struct socket *sock,
if (err)
goto out;

+ memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
+
+ err = vsock_assign_transport(vsk, NULL);
+ if (err)
+ goto out;
+
if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
remote_addr->svm_port)) {
err = -EINVAL;
goto out;
}

- memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
sock->state = SS_CONNECTED;

/* sock map disallows redirection of non-TCP sockets with sk_state !=
@@ -2487,7 +2527,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)

t_h2g = transport_h2g;
t_g2h = transport_g2h;
- t_dgram = transport_dgram;
+ t_dgram = transport_dgram_fallback;
t_local = transport_local;

if (features & VSOCK_TRANSPORT_F_H2G) {
@@ -2506,7 +2546,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
t_g2h = t;
}

- if (features & VSOCK_TRANSPORT_F_DGRAM) {
+ if (features & VSOCK_TRANSPORT_F_DGRAM_FALLBACK) {
if (t_dgram) {
err = -EBUSY;
goto err_busy;
@@ -2524,7 +2564,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)

transport_h2g = t_h2g;
transport_g2h = t_g2h;
- transport_dgram = t_dgram;
+ transport_dgram_fallback = t_dgram;
transport_local = t_local;

err_busy:
@@ -2543,8 +2583,8 @@ void vsock_core_unregister(const struct vsock_transport *t)
if (transport_g2h == t)
transport_g2h = NULL;

- if (transport_dgram == t)
- transport_dgram = NULL;
+ if (transport_dgram_fallback == t)
+ transport_dgram_fallback = NULL;

if (transport_local == t)
transport_local = NULL;
diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 7f1ea434656d..c29000f2612a 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -551,11 +551,6 @@ static void hvs_destruct(struct vsock_sock *vsk)
kfree(hvs);
}

-static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
-{
- return -EOPNOTSUPP;
-}
-
static int hvs_dgram_enqueue(struct vsock_sock *vsk,
struct sockaddr_vm *remote, struct msghdr *msg,
size_t dgram_len)
@@ -826,7 +821,6 @@ static struct vsock_transport hvs_transport = {
.connect = hvs_connect,
.shutdown = hvs_shutdown,

- .dgram_bind = hvs_dgram_bind,
.dgram_enqueue = hvs_dgram_enqueue,
.dgram_allow = hvs_dgram_allow,

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 66edffdbf303..ac2126c7dac5 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -428,7 +428,6 @@ static struct virtio_transport virtio_transport = {
.shutdown = virtio_transport_shutdown,
.cancel_pkt = virtio_transport_cancel_pkt,

- .dgram_bind = virtio_transport_dgram_bind,
.dgram_enqueue = virtio_transport_dgram_enqueue,
.dgram_allow = virtio_transport_dgram_allow,

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 01ea1402ad40..ffcbdd77feaa 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -781,13 +781,6 @@ bool virtio_transport_stream_allow(u32 cid, u32 port)
}
EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);

-int virtio_transport_dgram_bind(struct vsock_sock *vsk,
- struct sockaddr_vm *addr)
-{
- return -EOPNOTSUPP;
-}
-EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
-
bool virtio_transport_dgram_allow(u32 cid, u32 port)
{
return false;
diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
index 0bbbdb222245..857b0461f856 100644
--- a/net/vmw_vsock/vmci_transport.c
+++ b/net/vmw_vsock/vmci_transport.c
@@ -2072,7 +2072,7 @@ static int __init vmci_transport_init(void)
/* Register only with dgram feature, other features (H2G, G2H) will be
* registered when the first host or guest becomes active.
*/
- err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM);
+ err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM_FALLBACK);
if (err < 0)
goto err_unsubscribe;

diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
index 2a59dd177c74..278235ea06c4 100644
--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -61,7 +61,6 @@ static struct virtio_transport loopback_transport = {
.shutdown = virtio_transport_shutdown,
.cancel_pkt = vsock_loopback_cancel_pkt,

- .dgram_bind = virtio_transport_dgram_bind,
.dgram_enqueue = virtio_transport_dgram_enqueue,
.dgram_allow = virtio_transport_dgram_allow,

--
2.30.2