[Core][KV-transfer] MoRIIO: multi-node TP prefill→decode dispatch via published host list

[chaeminlim-mb]

Purpose

MoRIIO advertised a single peer host per instance. That breaks TP prefill→decode once the peer's TP group spans more than one host: a decode worker whose matching prefill rank lives on the second host still points at the first one, handshakes and reads the wrong KV, and the request wedges. It shows up in TP16 1P1D across two hosts. Single-host and TP<=8 deployments never hit it.

How it works

An instance already knows the ordered host list of its own TP group; this PR reads it from kv_connector_extra_config["node_hosts"] and publishes it at worker registration. The toy proxy forwards the prefill peer's list to the decode side as kv_transfer_params["remote_hosts"].

When a decode worker sets up a transfer, it resolves the peer host that actually owns the matching rank instead of always using the advertised head:

n_hosts        = len(remote_hosts)
ranks_per_node = tp_size // n_hosts          # 16 // 2 = 8
host           = remote_hosts[tp_rank // ranks_per_node]

In TP16 over two hosts, ranks 0–7 resolve to remote_hosts[0] and ranks 8–15 to remote_hosts[1]. If the peer is data-parallel and its DP ranks span the hosts, the same split runs on remote_dp_rank instead. That resolved host is exactly what the worker hands to the MoRIIO handshake and passes as remote_ip to the block read/write, so the transfer lands on the node that holds the slice rather than the head node.

Two paths stay bit-for-bit as before. With one host in the list (or none), the picker returns the original remote_host, so single-host and TP<=8 keep their current behavior. Directly-supplied peer hosts (remote_host, remote_hosts) are checked against kv_connector_extra_config["trusted_remote_hosts"] before use. A host parsed from the request_id (which can carry a client-supplied X-Request-Id) is checked too, but only when trusted_remote_hosts is set: leave it unset and the default flow is unchanged; set it — recommended when the endpoint is reachable by untrusted clients — and no crafted request can redirect a transfer to an off-list host.

Config lives entirely in kv_connector_extra_config; no new environment variable.

Independent of #46116. That PR decides which remote rank a decode reads from; this one decides which host that rank sits on. They edit nearby code in the read path, but neither depends on the other.

Test Plan

python -m pytest tests/v1/kv_connector/unit/test_moriio_multinode_hosts.py -q
ruff check vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_common.py vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_connector.py

Multi-host serving (manual, needs a two-host RDMA setup): TP16 prefill and TP16 decode across two hosts each, with node_hosts set for the local role and trusted_remote_hosts for the peer. Confirm each decode rank reads from the prefill host that holds its slice.

Test Result

test_moriio_multinode_hosts.py: 41 passed (CPU, no GPU). What they pin down:

• the rank→host split at the boundaries: for TP16 over two hosts, ranks 0–7 target remote_hosts[0] and ranks 8–15 target remote_hosts[1] (the exact mis-route above), plus the DP-rank variant;
• the wiring, not just the arithmetic: _pick_remote_host and _pick_host_for_dp_rank feed tp_rank / remote_dp_size into the picker, and their result is the host used for the handshake and the block read/write;
• single-host passthrough: remote_host comes back unchanged for any tp_rank;
• config parsing; the proxy forwarding the host list; and trust validation — an untrusted peer host is rejected before any handshake / notify / release send, whether it was supplied directly (remote_host / remote_hosts, always checked) or parsed from the request_id (checked when trusted_remote_hosts is configured), across every site that reads a peer host from kv_transfer_params.

ruff and py_compile pass on the changed files.

These tests cover the routing decision, which is where the bug was. They don't move real KV over RDMA; that needs two hosts with RDMA and isn't part of CI. The transfer path itself is unchanged, only the host it targets.

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[mergify]

Documentation preview: https://vllm--45228.org.readthedocs.build/en/45228/

[mergify]

Documentation preview: https://vllm--45228.org.readthedocs.build/en/45228/

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @chaeminlim-mb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[chaeminlim-mb]

Co-authored by @edwinlim0919 (Edwin Lim, MangoBoost) — credited in the commit trailers for this PR. Tagging him here so he is looped in and can follow the review.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @chaeminlim-mb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[claude]

Claude Code Review

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Claude Code Review

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[depthfirst-app]

⚪ Severity: LOW

In multi-node TP configurations where the peer's data-parallelism (DP) ranks span multiple hosts, _pick_remote_host omits remote_dp_size and remote_dp_rank arguments to _pick_remote_rank_host. This routes transfers based solely on tp_rank, potentially causing cross-user KV cache corruption or information leakage.
Helpful? Add 👍 / 👎

💡 Fix Suggestion

Suggestion: Pass meta.remote_dp_size and meta.remote_dp_rank to _pick_remote_rank_host in _pick_remote_host, so that DP-aware routing is used when the peer's DP ranks span multiple hosts. This makes _pick_remote_host consistent with _pick_host_for_dp_rank.

⚠️ Experimental Feature: This code suggestion is automatically generated. Please review carefully.

Suggested change

	def _pick_remote_host(self, meta: ReqMeta) -> str:
	def _pick_remote_host(self, meta: ReqMeta) -> str:
	"""Resolve the per-worker peer host for multi-node TP prefill-decode."""
	return _pick_remote_rank_host(
	meta.remote_host, meta.remote_hosts, int(meta.tp_size), self.tp_rank,
	int(meta.remote_dp_size), meta.remote_dp_rank,
	)

[depthfirst-app]

⚪ Severity: LOW

There is no validation on the ports parsed from kv_transfer_params or the request_id. An attacker can specify arbitrary ports (such as SSH or HTTP ports) on trusted hosts, forcing the engine to initiate outbound ZMQ connections to those ports.
Helpful? Add 👍 / 👎

💡 Fix Suggestion

Suggestion: Add port range validation after converting remote_notify_port to an integer. Create a helper function (e.g., validate_moriio_remote_port) in moriio_common.py that checks the port is within a valid range (e.g., 1024–65535 for non-privileged ports), and call it at both locations where remote_notify_port = int(remote_notify_port) is used (around line 577 in _release_write_prefill_blocks and around line 656 in the other method). For example:

def validate_moriio_remote_port(port: int, config_key: str) -> None:
    if not (1024 <= port <= 65535):
        raise ValueError(f"{config_key} contains invalid port: {port}")

Then after each remote_notify_port = int(remote_notify_port), add:

validate_moriio_remote_port(remote_notify_port, "remote_notify_port")

This prevents attackers from specifying well-known service ports (e.g., 22, 80, 443) on trusted hosts via a crafted request_id.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @chaeminlim-mb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork