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Diffstat (limited to 'Documentation/admin-guide/sysctl/net.rst')
| -rw-r--r-- | Documentation/admin-guide/sysctl/net.rst | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst index 3b2ad61995d4..0724a793798f 100644 --- a/Documentation/admin-guide/sysctl/net.rst +++ b/Documentation/admin-guide/sysctl/net.rst @@ -602,3 +602,31 @@ 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, or if no H2G transport is loaded at all, 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()``. + +Note: With this sysctl enabled, user space that attempts to talk to a guest +CID which is not implemented by the H2G transport will create host vsock +traffic. Environments that rely on H2G-only isolation should set it to 0. + +Values: + + - 0 - Connections to CIDs <= 2 or with VMADDR_FLAG_TO_HOST use G2H; + all others use H2G (or fail with ENODEV if H2G is not loaded). + - 1 - Connections to CIDs not owned by H2G fall back to G2H. (default) |