[PATCH] vsock: Enable H2G override
From: Alexander Graf <graf@amazon.com>
Date: 2026-03-02 10:41:47
Also in:
kvm, lkml, virtualization
Subsystem:
networking [general], the rest, virtio and vhost vsock driver, virtio host (vhost), vm sockets (af_vsock) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Stefan Hajnoczi, Stefano Garzarella, "Michael S. Tsirkin", Jason Wang
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 trivially 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. That means that for CID > 2, we really want an overlay. By default, all CIDs are owned by the hypervisor. But if vhost registers a CID, it takes precedence. Implement that logic. Vhost already knows which CIDs it supports anyway. With this logic, I can run a Nitro Enclave as well as a nested VM with vhost-vsock support in parallel, with the parent instance able to communicate to both simultaneously. Signed-off-by: Alexander Graf <graf@amazon.com> --- drivers/vhost/vsock.c | 11 +++++++++++ include/net/af_vsock.h | 3 +++ net/vmw_vsock/af_vsock.c | 3 +++ 3 files changed, 17 insertions(+)
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 054f7a718f50..223da817e305 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c@@ -91,6 +91,16 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid, struct net *net) return NULL; } +static bool vhost_transport_has_cid(u32 cid) +{ + bool found; + + rcu_read_lock(); + found = vhost_vsock_get(cid) != NULL; + rcu_read_unlock(); + return found; +} + static void vhost_transport_do_send_pkt(struct vhost_vsock *vsock, struct vhost_virtqueue *vq)
@@ -424,6 +434,7 @@ static struct virtio_transport vhost_transport = { .module = THIS_MODULE, .get_local_cid = vhost_transport_get_local_cid, + .has_cid = vhost_transport_has_cid, .init = virtio_transport_do_socket_init, .destruct = virtio_transport_destruct,
diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 533d8e75f7bb..4cdcb72f9765 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_cid)(u32 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..8b34b264b246 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c@@ -584,6 +584,9 @@ 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 (transport_h2g->has_cid && + !transport_h2g->has_cid(remote_cid)) + new_transport = transport_g2h; else new_transport = transport_h2g; break;
--
2.47.1
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