Vsock maintains a single CID number space which can be used to communicate to the host (G2H) or to a child-VM (H2G). The current logic assumes that G2H is only relevant for CID <= 2 because these target the hypervisor. However, in environments like Nitro Enclaves, an instance that hosts vhost_vsock powered VMs may still want to communicate to Enclaves that are reachable at higher CIDs through virtio-vsock-pci.
Vsock introduced VMADDR_FLAG_TO_HOST to allow user space applications to clearly express a desire to talk to the host instead of a guest via the passed target CID. However, users may not actually know which one they want to talk to and the application ecosystem has not picked up a way for users to specify that desire. Instead, make it easy for users and introduce a G2H fallback mechanism: when user space attempts to connect to a CID and the H2G transport (vhost-vsock / VMCI) does not own it, automatically route the connection through the G2H transport. This provides a single unified CID address space where vhost-registered CIDs go to nested VMs and all other CIDs are routed to the hypervisor. To give user space at least a hint that the kernel applied this logic, automatically set the VMADDR_FLAG_TO_HOST on the remote address so it can determine the path taken via getpeername(). To force the system back into old behavior, provide a sysctl (net.vsock.g2h_fallback, defaults to 1). Signed-off-by: Alexander Graf <[email protected]> --- v1 -> v2: - Rebase on 7.0, include namespace support - Add net.vsock.g2h_fallback sysctl - Rework description - Set VMADDR_FLAG_TO_HOST automatically - Add VMCI support - Update vsock_assign_transport() comment --- Documentation/admin-guide/sysctl/net.rst | 22 ++++++++++++++++++++++ drivers/misc/vmw_vmci/vmci_context.c | 1 + drivers/vhost/vsock.c | 13 +++++++++++++ include/linux/vmw_vmci_api.h | 1 + include/net/af_vsock.h | 3 +++ net/vmw_vsock/af_vsock.c | 20 +++++++++++++++++++- net/vmw_vsock/vmci_transport.c | 6 ++++++ 7 files changed, 65 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst index 3b2ad61995d4..cc364baa9021 100644 --- a/Documentation/admin-guide/sysctl/net.rst +++ b/Documentation/admin-guide/sysctl/net.rst @@ -602,3 +602,25 @@ it does not modify the current namespace or any existing children. A namespace with ``ns_mode`` set to ``local`` cannot change ``child_ns_mode`` to ``global`` (returns ``-EPERM``). + +g2h_fallback +------------ + +Controls whether connections to CIDs not owned by the host-to-guest (H2G) +transport automatically fall back to the guest-to-host (G2H) transport. + +When enabled, if a connect targets a CID that the H2G transport (e.g. +vhost-vsock) does not serve, the connection is routed via the G2H transport +(e.g. virtio-vsock) instead. This allows a host running both nested VMs +(via vhost-vsock) and sibling VMs reachable through the hypervisor (e.g. +Nitro Enclaves) to address both using a single CID space, without requiring +applications to set ``VMADDR_FLAG_TO_HOST``. + +When the fallback is taken, ``VMADDR_FLAG_TO_HOST`` is automatically set on +the remote address so that userspace can determine the path via +``getpeername()``. + +Values: + + - 0 - Connections to CIDs < 3 get handled by G2H, others by H2G. + - 1 - Connections to CIDs not owned by H2G fall back to G2H. (default) diff --git a/drivers/misc/vmw_vmci/vmci_context.c b/drivers/misc/vmw_vmci/vmci_context.c index 19ca00feed6e..577296784df5 100644 --- a/drivers/misc/vmw_vmci/vmci_context.c +++ b/drivers/misc/vmw_vmci/vmci_context.c @@ -364,6 +364,7 @@ bool vmci_ctx_exists(u32 cid) rcu_read_unlock(); return exists; } +EXPORT_SYMBOL_GPL(vmci_ctx_exists); /* * Retrieves VMCI context corresponding to the given cid. diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c index 054f7a718f50..319e3a690108 100644 --- a/drivers/vhost/vsock.c +++ b/drivers/vhost/vsock.c @@ -91,6 +91,18 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid, struct net *net) return NULL; } +static bool vhost_transport_has_remote_cid(struct vsock_sock *vsk, u32 cid) +{ + struct sock *sk = sk_vsock(vsk); + struct net *net = sock_net(sk); + bool found; + + rcu_read_lock(); + found = vhost_vsock_get(cid, net) != NULL; + rcu_read_unlock(); + return found; +} + static void vhost_transport_do_send_pkt(struct vhost_vsock *vsock, struct vhost_virtqueue *vq) @@ -424,6 +436,7 @@ static struct virtio_transport vhost_transport = { .module = THIS_MODULE, .get_local_cid = vhost_transport_get_local_cid, + .has_remote_cid = vhost_transport_has_remote_cid, .init = virtio_transport_do_socket_init, .destruct = virtio_transport_destruct, diff --git a/include/linux/vmw_vmci_api.h b/include/linux/vmw_vmci_api.h index 41764a684423..c412d17c572f 100644 --- a/include/linux/vmw_vmci_api.h +++ b/include/linux/vmw_vmci_api.h @@ -37,6 +37,7 @@ int vmci_doorbell_create(struct vmci_handle *handle, u32 flags, int vmci_doorbell_destroy(struct vmci_handle handle); u32 vmci_get_context_id(void); bool vmci_is_context_owner(u32 context_id, kuid_t uid); +bool vmci_ctx_exists(u32 cid); int vmci_register_vsock_callback(vmci_vsock_cb callback); int vmci_event_subscribe(u32 event, diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index 533d8e75f7bb..0aeb25642827 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -179,6 +179,9 @@ struct vsock_transport { /* Addressing. */ u32 (*get_local_cid)(void); + /* Check if this transport serves a specific remote CID. */ + bool (*has_remote_cid)(struct vsock_sock *vsk, u32 remote_cid); + /* Read a single skb */ int (*read_skb)(struct vsock_sock *, skb_read_actor_t); diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 2f7d94d682cb..b41bc734d6c0 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -210,6 +210,8 @@ static const struct vsock_transport *transport_dgram; static const struct vsock_transport *transport_local; static DEFINE_MUTEX(vsock_register_mutex); +static int vsock_g2h_fallback = 1; + /**** UTILS ****/ /* Each bound VSocket is stored in the bind hash table and each connected @@ -547,7 +549,8 @@ static void vsock_deassign_transport(struct vsock_sock *vsk) * g2h is not loaded, will use local transport; * - remote CID <= VMADDR_CID_HOST or h2g is not loaded or remote flags field * includes VMADDR_FLAG_TO_HOST flag value, will use guest->host transport; - * - remote CID > VMADDR_CID_HOST will use host->guest transport; + * - remote CID > VMADDR_CID_HOST will use host->guest transport if h2g has + * registered that CID, otherwise will use guest->host transport (overlay); */ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) { @@ -584,6 +587,12 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) else if (remote_cid <= VMADDR_CID_HOST || !transport_h2g || (remote_flags & VMADDR_FLAG_TO_HOST)) new_transport = transport_g2h; + else if (vsock_g2h_fallback && + transport_h2g->has_remote_cid && + !transport_h2g->has_remote_cid(vsk, remote_cid)) { + vsk->remote_addr.svm_flags |= VMADDR_FLAG_TO_HOST; + new_transport = transport_g2h; + } else new_transport = transport_h2g; break; @@ -2879,6 +2888,15 @@ static struct ctl_table vsock_table[] = { .mode = 0644, .proc_handler = vsock_net_child_mode_string }, + { + .procname = "g2h_fallback", + .data = &vsock_g2h_fallback, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, }; static int __net_init vsock_sysctl_register(struct net *net) diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c index 4296ca1183f1..de3dff52c566 100644 --- a/net/vmw_vsock/vmci_transport.c +++ b/net/vmw_vsock/vmci_transport.c @@ -2045,6 +2045,11 @@ static u32 vmci_transport_get_local_cid(void) return vmci_get_context_id(); } +static bool vmci_transport_has_remote_cid(struct vsock_sock *vsk, u32 cid) +{ + return vmci_ctx_exists(cid); +} + static struct vsock_transport vmci_transport = { .module = THIS_MODULE, .init = vmci_transport_socket_init, @@ -2074,6 +2079,7 @@ static struct vsock_transport vmci_transport = { .notify_send_post_enqueue = vmci_transport_notify_send_post_enqueue, .shutdown = vmci_transport_shutdown, .get_local_cid = vmci_transport_get_local_cid, + .has_remote_cid = vmci_transport_has_remote_cid, }; static bool vmci_check_transport(struct vsock_sock *vsk) -- 2.47.1 Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597
