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

From: Bobby Eshleman
Date: Wed Aug 02 2023 - 20:53:30 EST

On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
> On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
> >
> >
> > On 19.07.2023 03:50, Bobby Eshleman wrote:
> > > 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@xxxxxxxxxxxxx>
> > > ---
> > > 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);
> >
> > I'm a little bit confused about this:
> > 1) Let's create SOCK_DGRAM socket using vsock_create()
> > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
> > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
> > correct I think...
> >
> > Please correct me if i'm wrong
> >
> > Thanks, Arseniy
> >
>
> As I understand, for the VMCI case, if transport_h2g != NULL, then
> transport_h2g == transport_dgram_fallback. In either case,
> vsk->transport == transport_dgram_fallback.
>
> For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
> but it is unused because vsk->transport->dgram_bind == NULL.
>
> Until SS_CONNECTED is set by connect() and vsk->transport is set
> correctly, the send path is barred from using the bad transport.
>
> I guess the recvmsg() path is a little more sketchy, and probably only
> works in my test cases because h2g/g2h in the vhost/virtio case have
> identical dgram_addr_init() implementations.
>
> I think a cleaner solution is maybe checking in vsock_create() if
> dgram_bind is implemented. If it is not, then vsk->transport should be
> reset to NULL and a comment added explaining why VMCI requires this.
>
> Then the other calls can begin explicitly checking for vsk->transport ==
> NULL.

Actually, on further reflection here, in order for the vsk->transport to
be called in time for ->dgram_addr_init(), it is going to be necessary
to call vsock_assign_transport() in vsock_dgram_bind() anyway.

I think this means that the vsock_assign_transport() call can be removed
from vsock_create() call entirely, and yet VMCI can still dispatch
messages upon bind() calls as needed.

This would then simplify the whole arrangement, if there aren't other
unseen issues.

>
> Thoughts?
>
> > > 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,
> > >
> > >