[NIXL][Mamba][3/N] Heterogeneous TP: 3-read conv state transfer (#37635)

tests/v1/kv_connector/nixl_integration/config_sweep_accuracy_test.sh

@@ -19,9 +19,9 @@ dp_ep_configs=(
 "DP_EP=1 GPU_MEMORY_UTILIZATION=0.8 PREFILLER_TP_SIZE=2 DECODER_TP_SIZE=2 MODEL_NAMES=deepseek-ai/deepseek-vl2-tiny" # MLA+P-TP2, D-DPEP=2 (TP=1)
 )
 hybrid_ssm_configs=(
-  "ENABLE_HMA_FLAG=1 GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=ibm-granite/granite-4.0-h-tiny VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192,--trust-remote-code"
+  "VLLM_SSM_CONV_STATE_LAYOUT=DS ENABLE_HMA_FLAG=1 GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=ibm-granite/granite-4.0-h-tiny VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192,--trust-remote-code"
   # TODO: (NickLucche) Address async scheduling issue with TP>1 separately as this may impact other models.
-  "ENABLE_HMA_FLAG=1 PREFILLER_TP_SIZE=2 DECODER_TP_SIZE=2 GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=ibm-granite/granite-4.0-h-tiny VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192,--trust-remote-code,--no-async-scheduling"
+  "VLLM_SSM_CONV_STATE_LAYOUT=DS ENABLE_HMA_FLAG=1 PREFILLER_TP_SIZE=2 DECODER_TP_SIZE=2 GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=ibm-granite/granite-4.0-h-tiny VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192,--trust-remote-code,--no-async-scheduling"
 )
 sw_attn_configs=(
   "ENABLE_HMA_FLAG=1 GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=google/gemma-3-4b-it PREFILLER_TP_SIZE=1 DECODER_TP_SIZE=2 VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192"

tests/v1/kv_connector/unit/test_nixl_connector_hma.py

@@ -224,6 +224,8 @@ def test_get_block_descs_ids_hybrid_ssm():
     worker._has_mamba = True
     worker._is_mamba_group = [False, True]
     worker._physical_blocks_per_logical_kv_block = 1
+    worker._mamba_phys_ratio = {engine_id: 1}
+    worker.block_len_per_layer = [100]
     # num_descs = num_regions * num_blocks (no blocks_first doubling)
     worker.num_descs = 2 * num_blocks
 
@@ -234,9 +236,10 @@ def test_get_block_descs_ids_hybrid_ssm():
     # FA group: stride=num_blocks=100, offset=0
     #   region0: [3, 5],  region1: [103, 105]
     # SSM group: stride=logical_blocks=100 (=num_blocks/ratio=100/1),
-    #   offset=num_descs=200
-    #   region0: [201, 202],  region1: [301, 302]
-    expected = [3, 5, 103, 105, 201, 202, 301, 302]
+    #   offset=num_fa_descs=200, 4 regions per Mamba layer (x, B, C, ssm)
+    #   region0: [201, 202], region1: [301, 302],
+    #   region2: [401, 402], region3: [501, 502]
+    expected = [3, 5, 103, 105, 201, 202, 301, 302, 401, 402, 501, 502]
     assert list(result) == expected, f"Expected {expected}, got {list(result)}"
 
 
@@ -259,6 +262,8 @@ def test_get_block_descs_ids_kernel_block_mismatch():
     worker._has_mamba = True
     worker._is_mamba_group = [False, True]
     worker._physical_blocks_per_logical_kv_block = ratio
+    worker._mamba_phys_ratio = {engine_id: ratio}
+    worker.block_len_per_layer = [100]
     worker.num_descs = 2 * num_blocks  # 800
 
     fa_blocks = [3, 7]  # kernel-level block IDs
@@ -267,9 +272,11 @@ def test_get_block_descs_ids_kernel_block_mismatch():
 
     # FA group: stride=num_blocks=400, offset=0
     #   region0: [3, 7],  region1: [403, 407]
-    # SSM group: stride=logical_blocks=400//4=100, offset=num_descs=800
-    #   region0: [801, 802],  region1: [901, 902]
-    expected = [3, 7, 403, 407, 801, 802, 901, 902]
+    # SSM group: stride=logical_blocks=400//4=100, offset=num_fa_descs=800,
+    #   4 regions per Mamba layer (x, B, C, ssm)
+    #   region0: [801, 802], region1: [901, 902],
+    #   region2: [1001, 1002], region3: [1101, 1102]
+    expected = [3, 7, 403, 407, 801, 802, 901, 902, 1001, 1002, 1101, 1102]
     assert list(result) == expected, f"Expected {expected}, got {list(result)}"
 
 
@@ -418,3 +425,29 @@ def test_has_mamba_init(
     )
     assert scheduler._has_mamba is expected_has_mamba
     assert scheduler._is_hma_required is expected_is_hma
+
+
+@pytest.mark.cpu_test
+@pytest.mark.parametrize(
+    "ssm_sizes,block_len,expected_ratio",
+    [
+        # Nemotron 30B TP=1: ceil((36864 + 2097152) / 8192) = 261
+        ((36864, 2097152), 8192, 261),
+        # Nemotron 30B TP=2: ceil((18432 + 1048576) / 4096) = 261
+        ((18432, 1048576), 4096, 261),
+        # Nemotron 30B TP=4: ceil((9216 + 524288) / 4096) = 131
+        ((9216, 524288), 4096, 131),
+    ],
+)
+def test_compute_mamba_phys_ratio(ssm_sizes, block_len, expected_ratio):
+    """Verify that compute_mamba_phys_ratio is TP-dependent.
+
+    With dimension-sharded Mamba state, the ratio differs across TP sizes
+    (e.g. TP=1 → 261, TP=4 → 131 for Nemotron 30B). This is why
+    _mamba_phys_ratio must be stored per-engine.
+    """
+    from vllm.distributed.kv_transfer.kv_connector.v1.ssm_conv_transfer_utils import (
+        compute_mamba_phys_ratio,
+    )
+
+    assert compute_mamba_phys_ratio(ssm_sizes, block_len) == expected_ratio

vllm/distributed/kv_transfer/kv_connector/utils.py

@@ -5,7 +5,7 @@ KV cache helper for store.
 """
 
 from collections.abc import Iterator
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any, Literal, cast
 
 import torch
@@ -516,6 +516,338 @@ class TpKVTopology:
         return cache if self.split_k_and_v else [cache]
 
 
+# ---- Mamba-HMA hetero-TP transfer config ----
+#
+# Key insight: with hetero-TP (P_TP > D_TP), FA KV cache may be
+# replicated across P ranks (when P_TP > num_kv_heads), but Mamba
+# conv/SSM state is almost always uniquely sharded per P rank.  So the
+# number of P ranks D must read from can differ between FA and Mamba,
+# and they must be handled separately.
+
+
+def _physical_head_range(tp_size: int, num_heads: int, rank: int) -> range:
+    """Physical KV head range stored in a rank's KV cache tensor.
+
+    When ``tp_size <= num_heads``: sharded, K/TP contiguous heads per rank.
+    When ``tp_size > num_heads``: 1 physical head per rank.  Heads are
+    distributed **contiguously** (matching vLLM's GQA weight partitioning):
+    consecutive ranks share a head before moving to the next one.
+    """
+    if tp_size <= num_heads:
+        assert num_heads % tp_size == 0
+        per_rank = num_heads // tp_size
+        return range(rank * per_rank, (rank + 1) * per_rank)
+    else:
+        h = rank * num_heads // tp_size
+        return range(h, h + 1)
+
+
+def _range_overlap(a: range, b: range) -> range:
+    start = max(a.start, b.start)
+    stop = min(a.stop, b.stop)
+    return range(start, max(start, stop))
+
+
+@dataclass
+class HeteroTPTransferConfig:
+    """Precomputed transfer plan for one (D rank, P engine) pair.
+
+    Currently only instantiated for Mamba-HMA (hybrid SSM+Attention) models
+    where FA and mamba require different splitting factors.  Could be extended
+    to other model types that need non-uniform hetero-TP transfer sizing.
+
+    All descriptor sizes are computed here.  The guarantee is:
+        local_entry_size == remote_entry_size   (for NIXL)
+
+    Attributes that start with ``fa_`` concern FlashAttention KV cache.
+    Attributes that start with ``mamba_`` concern Mamba conv/SSM state.
+    """
+
+    # ---- Input parameters (from handshake) ----
+    tp_ratio: int
+    K: int  # total_num_kv_heads (before TP sharding)
+    d_tp: int  # D engine's tensor_parallel_size
+    p_tp: int  # P engine's tensor_parallel_size
+    d_rank: int  # this D worker's TP rank
+    use_mla: bool
+
+    # Per-layer block lengths (bytes, K+V combined for blocks_first).
+    # Uniform across layers for current models.
+    d_block_len: int  # D's block_len_per_layer (representative)
+    p_block_len: int  # P's block_len_per_layer (from handshake)
+    is_blocks_first: bool  # kv_topo.is_kv_layout_blocks_first
+
+    # ---- Derived: computed in __post_init__ ----
+    #
+    # Physical heads per rank (what the KV tensor actually stores)
+    d_physical_heads: int = field(init=False)
+    p_physical_heads: int = field(init=False)
+
+    # How many distinct P ranks D needs for FA data
+    physical_fa_num_reads: int = field(init=False)
+
+    # Which P ranks contribute unique FA heads (ordered by head index)
+    fa_read_targets: list[int] = field(init=False)
+
+    # All P ranks needed for mamba (always abs_tp for tp_ratio < 0)
+    mamba_num_reads: int = field(init=False)
+
+    # All P ranks this D rank communicates with (FA ∪ mamba)
+    transfer_targets: list[int] = field(init=False)
+
+    # FA descriptor entry size (K or V side, for blocks_first layout)
+    # Guaranteed: fa_entry_size is the SAME for local handle AND remote desc.
+    fa_entry_size: int = field(init=False)
+
+    # Replication flags
+    is_d_replicated: bool = field(init=False)
+    is_p_replicated: bool = field(init=False)
+
+    # Pre-built set for fast lookup
+    _fa_target_set: frozenset[int] = field(init=False, repr=False)
+    # Map: P rank → index in fa_read_targets (for head slot offset)
+    _fa_target_index: dict[int, int] = field(init=False, repr=False)
+
+    def __post_init__(self) -> None:
+        K = self.K
+        self.is_d_replicated = self.d_tp > K
+        self.is_p_replicated = self.p_tp > K
+
+        self.d_physical_heads = max(1, K // self.d_tp)
+        self.p_physical_heads = max(1, K // self.p_tp)
+
+        abs_tp = -self.tp_ratio if self.tp_ratio < 0 else 1
+
+        # ---- Mamba range (computed first so FA can prefer ranks in it) ----
+        mamba_range: range | None = None
+        if self.tp_ratio < 0:
+            mamba_range = range(self.d_rank * abs_tp, (self.d_rank + 1) * abs_tp)
+
+        # ---- FA read targets ----
+        if self.use_mla or self.tp_ratio >= 0:
+            self.physical_fa_num_reads = 1
+            self.fa_read_targets = (
+                [0]
+                if self.use_mla
+                # Must match kv_topo.get_target_remote_ranks (d_rank // tp_ratio).
+                else [
+                    self.d_rank // self.tp_ratio if self.tp_ratio > 0 else self.d_rank
+                ]
+            )
+        else:
+            d_needs = _physical_head_range(self.d_tp, K, self.d_rank)
+            # When mamba range exists, prefer P ranks within it so that
+            # FA targets are a subset of mamba transfer_targets (avoids
+            # orphaned FA targets outside the transfer loop).
+            search_range = mamba_range if mamba_range is not None else range(self.p_tp)
+            seen: set[tuple[int, int]] = set()
+            targets: list[int] = []
+            for p in search_range:
+                p_has = _physical_head_range(self.p_tp, K, p)
+                ov = _range_overlap(d_needs, p_has)
+                if len(ov) > 0:
+                    key = (ov.start, ov.stop)
+                    if key not in seen:
+                        seen.add(key)
+                        targets.append(p)
+            if not targets:
+                # Fallback: search globally (should not happen in practice)
+                for p in range(self.p_tp):
+                    p_has = _physical_head_range(self.p_tp, K, p)
+                    ov = _range_overlap(d_needs, p_has)
+                    if len(ov) > 0:
+                        key = (ov.start, ov.stop)
+                        if key not in seen:
+                            seen.add(key)
+                            targets.append(p)
+            self.fa_read_targets = targets
+            self.physical_fa_num_reads = len(targets)
+
+        self._fa_target_set = frozenset(self.fa_read_targets)
+        self._fa_target_index = {r: i for i, r in enumerate(self.fa_read_targets)}
+
+        # ---- Mamba targets ----
+        if mamba_range is not None and abs_tp > self.physical_fa_num_reads:
+            self.mamba_num_reads = abs_tp
+            self.transfer_targets = list(mamba_range)
+        else:
+            self.mamba_num_reads = self.physical_fa_num_reads
+            self.transfer_targets = list(self.fa_read_targets)
+
+        # ---- FA entry size ----
+        # For blocks_first: block_len_per_layer includes K+V; // 2 gives K (or V).
+        # Use min(D, P) because D indexes into P when tp_ratio > 0,
+        # and P is the natural unit when tp_ratio < 0.
+        effective_block_len = min(self.d_block_len, self.p_block_len)
+        if self.is_blocks_first:
+            self.fa_entry_size = effective_block_len // 2
+        else:
+            self.fa_entry_size = effective_block_len
+
+        self._validate()
+
+    def _validate(self) -> None:
+        """Cross-check internal consistency."""
+        if self.is_d_replicated and self.is_p_replicated and self.tp_ratio > 0:
+            logger.info(
+                "Both-replicated hetero-TP: D_TP=%d > P_TP=%d > K=%d. "
+                "Using d_rank // tp_ratio routing with relative head offset.",
+                self.d_tp,
+                self.p_tp,
+                self.K,
+            )
+
+        # FA targets must be a subset of transfer_targets
+        tt_set = set(self.transfer_targets)
+        for t in self.fa_read_targets:
+            if t not in tt_set:
+                logger.error(
+                    "FA target P rank %d is NOT in transfer_targets %s. "
+                    "This will cause missed FA reads!",
+                    t,
+                    self.transfer_targets,
+                )
+
+        # For tp_ratio < 0 with blocks_first: D_K_half / reads should == P_K_half
+        if (
+            self.is_blocks_first
+            and self.tp_ratio < 0
+            and self.physical_fa_num_reads > 0
+        ):
+            d_k_half = self.d_block_len // 2
+            p_k_half = self.p_block_len // 2
+            expected_local = d_k_half // self.physical_fa_num_reads
+            if expected_local != p_k_half:
+                logger.warning(
+                    "FA size mismatch: D_K_half=%d / reads=%d = %d, "
+                    "but P_K_half=%d.  This may indicate a head count or "
+                    "Mamba-HMA inflation inconsistency.",
+                    d_k_half,
+                    self.physical_fa_num_reads,
+                    expected_local,
+                    p_k_half,
+                )
+
+    # ---- Query methods ----
+
+    def should_skip_fa(self, p_rank: int) -> bool:
+        """Whether to skip FA groups for this P rank (mamba-only transfer)."""
+        return p_rank not in self._fa_target_set
+
+    def fa_head_slot(self, p_rank: int) -> int:
+        """Index into D's FA block for this P rank's head data.
+
+        For P ranks in fa_read_targets, returns 0, 1, ..., reads-1.
+        For P ranks NOT in fa_read_targets (replicated duplicates),
+        returns the slot of the matching FA target with the same head.
+        """
+        if p_rank in self._fa_target_index:
+            return self._fa_target_index[p_rank]
+        # Duplicate head: find which fa_target has the same physical head
+        p_head = _physical_head_range(self.p_tp, self.K, p_rank)
+        for target in self.fa_read_targets:
+            t_head = _physical_head_range(self.p_tp, self.K, target)
+            if _range_overlap(p_head, t_head):
+                return self._fa_target_index[target]
+        return 0  # fallback
+
+    def fa_rank_offset(self, remote_kv_block_len: int) -> int:
+        """Byte offset into P's FA block for this D rank.
+
+        When D is replicated (D_TP > K), multiple D ranks share a head.
+        Computes offset *relative to the target P rank's first head*
+        so it works regardless of how many heads P has.
+        When neither side replicates, falls back to tp_rank % tp_ratio.
+        Returns 0 when D does not index into P's block.
+        """
+        if self.use_mla or self.tp_ratio <= 0:
+            return 0
+        if self.is_d_replicated:
+            d_head = self.d_rank * self.K // self.d_tp
+            p_rank = self.fa_read_targets[0]
+            p_start = p_rank * self.K // self.p_tp
+            return (d_head - p_start) * remote_kv_block_len
+        return self.d_rank % self.tp_ratio * remote_kv_block_len
+
+    @property
+    def needs_split_handles(self) -> bool:
+        """Whether per-P-rank split handles are needed.
+
+        True when FA and mamba have different read counts, requiring
+        different splitting factors in the local handle.
+        """
+        return self.tp_ratio < 0 and not self.use_mla and len(self.transfer_targets) > 1
+
+    def compute_split_handle_data(
+        self,
+        src_blocks_data: list[tuple[int, int, int]],
+        num_fa_descs: int,
+        abs_tp: int,
+    ) -> list[list[tuple[int, int, int]]]:
+        """Compute per-P-rank (addr, len, tp) triples for Mamba-HMA split handles.
+
+        FA descriptors (indices < num_fa_descs) are sliced by
+        ``physical_fa_num_reads``; mamba descriptors are sliced uniformly
+        by ``abs_tp``.
+
+        Returns one list of triples per transfer target.
+        """
+        all_handle_data: list[list[tuple[int, int, int]]] = []
+        for p_idx, p_rank in enumerate(self.transfer_targets):
+            handle_data: list[tuple[int, int, int]] = []
+            skip_fa = self.should_skip_fa(p_rank)
+            fa_slot = self.fa_head_slot(p_rank) if not skip_fa else 0
+
+            for j, (addr, local_len, tp) in enumerate(src_blocks_data):
+                if j < num_fa_descs:
+                    assert self.physical_fa_num_reads >= 1
+                    fa_chunk = local_len // self.physical_fa_num_reads
+                    handle_data.append((addr + fa_slot * fa_chunk, fa_chunk, tp))
+                else:
+                    mamba_chunk = local_len // abs_tp
+                    handle_data.append((addr + p_idx * mamba_chunk, mamba_chunk, tp))
+            all_handle_data.append(handle_data)
+        return all_handle_data
+
+    def filter_block_ids_for_rank(
+        self,
+        remote_rank: int,
+        local_ids: BlockIds,
+        remote_ids: BlockIds,
+        is_mamba_group: list[bool],
+    ) -> tuple[BlockIds, BlockIds]:
+        """Zero out FA groups for P ranks outside fa_read_targets.
+
+        Returns (filtered_local_ids, filtered_remote_ids).  When the
+        remote rank carries FA data for this D rank, returns the inputs
+        unchanged.
+        """
+        if not self.should_skip_fa(remote_rank):
+            return local_ids, remote_ids
+        num_groups = len(local_ids)
+        filtered_local: list[list[int]] = [
+            [] if not is_mamba_group[g] else local_ids[g] for g in range(num_groups)
+        ]
+        filtered_remote: list[list[int]] = [
+            [] if not is_mamba_group[g] else remote_ids[g] for g in range(num_groups)
+        ]
+        return filtered_local, filtered_remote
+
+    def describe(self) -> str:
+        """One-line summary for logging."""
+        return (
+            f"HeteroTPTransferConfig("
+            f"tp_ratio={self.tp_ratio}, K={self.K}, "
+            f"d_tp={self.d_tp}, p_tp={self.p_tp}, d_rank={self.d_rank}, "
+            f"physical_fa_reads={self.physical_fa_num_reads}, "
+            f"mamba_reads={self.mamba_num_reads}, "
+            f"fa_targets={self.fa_read_targets}, "
+            f"transfer_targets={self.transfer_targets}, "
+            f"fa_entry_size={self.fa_entry_size}, "
+            f"d_block_len={self.d_block_len}, p_block_len={self.p_block_len})"
+        )
+
+
 def get_current_attn_backends(
     vllm_config: VllmConfig, layer_names: list[str] | None = None
 ) -> list[type[AttentionBackend]]:
@@ -559,3 +891,50 @@ def get_current_attn_backend(
 ) -> type[AttentionBackend]:
     """Get the first attention backend for the given layers."""
     return get_current_attn_backends(vllm_config, layer_names)[0]
+
+
+# TODO (ZhanqiuHu): Consolidate TpKVTopology and HeteroTPTransferConfig
+# into a single engine-agnostic TransferTopology class.
+# 6 of 9 HeteroTPTransferConfig init fields duplicate TpKVTopology data.
+#
+# @dataclass
+# class EngineTransferInfo:
+#     """Per-remote-engine transfer state, computed at handshake."""
+#     p_tp: int
+#     tp_ratio: int
+#     p_block_len: int
+#     block_size: int
+#     # Mamba-specific (None for non-mamba models)
+#     fa_read_targets: list[int] | None = None
+#     transfer_targets: list[int] | None = None
+#     physical_fa_num_reads: int | None = None
+#     mamba_num_reads: int | None = None
+#     fa_entry_size: int | None = None
+#
+# class TransferTopology:
+#     """Single source of truth for TP topology + transfer sizing."""
+#     # Shared (set once at init, replaces duplicate fields)
+#     tp_rank: int          # == TpKVTopology.tp_rank == HeteroTP.d_rank
+#     tp_size: int          # == TpKVTopology.tp_size == HeteroTP.d_tp
+#     total_num_kv_heads: int  # == HeteroTP.K
+#     is_mla: bool          # == HeteroTP.use_mla
+#     is_mamba: bool
+#     is_blocks_first: bool # == HeteroTP.is_blocks_first
+#     d_block_len: int
+#
+#     # Per-engine (populated via register_engine() at handshake)
+#     _engines: dict[EngineId, EngineTransferInfo]
+#
+#     def register_engine(self, engine_id, p_tp, p_block_len, ...): ...
+#
+#     # General (from TpKVTopology)
+#     def tp_ratio(self, engine_id) -> int: ...
+#     def target_remote_ranks(self, engine_id) -> list[int]: ...
+#     def is_kv_replicated(self, engine_id) -> bool: ...
+#
+#     # Mamba-specific (from HeteroTPTransferConfig, gated by is_mamba)
+#     def fa_rank_offset(self, engine_id, block_len) -> int: ...
+#     def physical_fa_num_reads(self, engine_id) -> int: ...
+#     def transfer_targets(self, engine_id) -> list[int]: ...
+#     def should_skip_fa(self, engine_id, p_rank) -> bool: ...
+#     def filter_block_ids_for_rank(self, engine_id, ...) -> ...: ...

vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py

@@ -25,6 +25,7 @@ from vllm.config import VllmConfig
 from vllm.distributed.kv_transfer.kv_connector.utils import (
     BlockIds,
     EngineId,
+    HeteroTPTransferConfig,
     TpKVTopology,
     get_current_attn_backend,
     get_current_attn_backends,
@@ -47,12 +48,18 @@ from vllm.distributed.kv_transfer.kv_connector.v1.metrics import (
     PromMetric,
     PromMetricT,
 )
+from vllm.distributed.kv_transfer.kv_connector.v1.ssm_conv_transfer_utils import (
+    MambaConvSplitInfo,
+    compute_mamba_phys_ratio,
+    derive_mamba_conv_split,
+)
 from vllm.distributed.parallel_state import (
     get_tensor_model_parallel_rank,
     get_tensor_model_parallel_world_size,
 )
 from vllm.forward_context import ForwardContext
 from vllm.logger import init_logger
+from vllm.model_executor.layers.mamba.mamba_utils import is_conv_state_dim_first
 from vllm.platforms import current_platform
 from vllm.utils.math_utils import cdiv
 from vllm.utils.network_utils import make_zmq_path, make_zmq_socket
@@ -1038,7 +1045,7 @@ class NixlConnectorWorker:
         }
         self.hma_group_size = len(kv_cache_config.kv_cache_tensors)
 
-        # Mamba metadata
+        # ---- Mamba model state (derived from model config) ----
         self._is_mamba_group = [
             isinstance(group.kv_cache_spec, MambaSpec)
             for group in kv_cache_config.kv_cache_groups
@@ -1065,6 +1072,17 @@ class NixlConnectorWorker:
                 ssm_shape.numel() * ssm_nbytes,
             )
         self._mamba_ssm_size = mamba_ssm_size
+        # Conv state sub-projection decomposition (None when no Mamba).
+        # The 3-read transfer requires DS (dim, state_len) conv layout so
+        # that x/B/C sub-projections are contiguous in memory.
+        self._conv_decomp: MambaConvSplitInfo | None = None
+        if self._has_mamba:
+            assert is_conv_state_dim_first(), (
+                "3-read Mamba conv transfer requires DS conv state layout. "
+                "Set VLLM_SSM_CONV_STATE_LAYOUT=DS"
+            )
+            local_tp = vllm_config.parallel_config.tensor_parallel_size
+            self._conv_decomp = derive_mamba_conv_split(mamba_spec, local_tp)
 
         # Agent.
         non_ucx_backends = [b for b in self.nixl_backends if b != "UCX"]
@@ -1175,6 +1193,16 @@ class NixlConnectorWorker:
         self.dst_num_blocks: dict[EngineId, int] = {}
         self._registered_descs: list[Any] = []
 
+        # ---- Mamba-HMA per-engine state (only used when self._has_mamba) ----
+        # Per-engine transfer config (source of truth for FA/mamba sizing).
+        self._transfer_configs: dict[str, HeteroTPTransferConfig] = {}
+        # NOTE (ZhanqiuHu): _mamba_phys_ratio MUST be per-engine.
+        # compute_mamba_phys_ratio = ceil((conv_bytes + ssm_bytes) / block_len)
+        # where conv/ssm bytes are per-TP-rank (dimension-sharded).  With
+        # heterogeneous TP the per-rank sizes differ, so the ratio differs:
+        #   e.g. Nemotron 30B: P(TP=4) → 131, D(TP=1) → 261.
+        self._mamba_phys_ratio: dict[EngineId, int] = {}
+
         # In progress transfers.
         # [req_id -> list[handle]]
         self._recving_metadata: dict[ReqId, ReqMeta] = {}
@@ -1701,8 +1729,7 @@ class NixlConnectorWorker:
             # then duplicate it logically to be able to index SSM/Conv separately.
             self.num_regions *= 2
 
-        # TODO (NickLucche) Adapt to different descs views (engine_id->tp_rank) to
-        # support heterogeneous TP.
+        # Total local FA descriptors (boundary between FA and mamba descs).
         self.num_descs = self.num_regions * self.num_blocks
 
         descs = self.nixl_wrapper.get_reg_descs(caches_data, self.nixl_memory_type)
@@ -1715,6 +1742,9 @@ class NixlConnectorWorker:
         self.dst_num_blocks[self.engine_id] = self.num_blocks
 
         if self._has_mamba:
+            self._mamba_phys_ratio[self.engine_id] = (
+                self._physical_blocks_per_logical_kv_block
+            )
             logger.info(
                 "Hybrid SSM registration: num_blocks=%s, "
                 "logical_num_blocks=%s, ratio=%s, num_regions=%s, "
@@ -1755,6 +1785,149 @@ class NixlConnectorWorker:
             agent_metadata_bytes=encoder.encode(agent_metadata),
         )
 
+    def _build_mamba_local(
+        self,
+        base_addresses: list[int],
+        block_size_ratio: int,
+    ) -> list[tuple[int, int, int]]:
+        """Build 4 desc regions (x, B, C, ssm) per layer for local mamba
+        blocks, enabling the 3-read transfer with DS conv layout."""
+        assert block_size_ratio == 1, (
+            "Mamba 3-read transfer with block_size_ratio != 1 is not tested. "
+            f"Got block_size_ratio={block_size_ratio}."
+        )
+        assert self._conv_decomp is not None
+        conv_offsets = self._conv_decomp.local_conv_offsets
+        conv_size, ssm_size = self._mamba_ssm_size
+        num_blocks = self._logical_num_blocks * block_size_ratio
+        phys_ratio = self._physical_blocks_per_logical_kv_block
+
+        result: list[tuple[int, int, int]] = []
+        for i, base_addr in enumerate(base_addresses):
+            page_stride = self.block_len_per_layer[i] // block_size_ratio * phys_ratio
+            for off, sz in conv_offsets:
+                for blk in range(num_blocks):
+                    result.append(
+                        (base_addr + blk * page_stride + off, sz, self.device_id)
+                    )
+            # SSM temporal state follows the conv state.
+            for blk in range(num_blocks):
+                result.append(
+                    (
+                        base_addr + blk * page_stride + conv_size,
+                        ssm_size,
+                        self.device_id,
+                    )
+                )
+        return result
+
+    def _build_fa_remote_for_mamba(
+        self,
+        nixl_agent_meta: NixlAgentMetadata,
+        transfer_cfg: HeteroTPTransferConfig,
+        block_size_ratio: int,
+        kv_topo: TpKVTopology,
+    ) -> list[tuple[int, int, int]]:
+        """Build remote FA descriptors for mamba models.
+
+        Uses transfer_cfg for GQA-aware FA divisor and head-based rank offset
+        instead of the standard uniform tp_ratio split.
+        """
+        assert block_size_ratio == 1, (
+            "Mamba 3-read transfer with block_size_ratio != 1 is not tested. "
+            f"Got block_size_ratio={block_size_ratio}."
+        )
+        # TODO (ZhanqiuHu): unify with register_remote_blocks when Mamba-HMA
+        # hetero-TP logic stabilizes.
+        tp_ratio = transfer_cfg.tp_ratio
+        result: list[tuple[int, int, int]] = []
+        for i, base_addr in enumerate(nixl_agent_meta.kv_caches_base_addr):
+            local_block_len = self.get_backend_aware_kv_block_len(
+                layer_idx=i, first_split=True, mamba_view=False
+            )
+            remote_kv_block_len = local_block_len // block_size_ratio
+            if block_size_ratio > 1:
+                local_block_len = remote_kv_block_len
+
+            if tp_ratio < 0 and not self.use_mla:
+                local_block_len = local_block_len // transfer_cfg.physical_fa_num_reads
+
+            rank_offset = transfer_cfg.fa_rank_offset(remote_kv_block_len)
+
+            num_blocks = nixl_agent_meta.num_blocks
+            page_size = nixl_agent_meta.block_lens[i]
+            for block_id in range(num_blocks):
+                block_offset = block_id * page_size
+                addr = base_addr + block_offset + rank_offset
+                result.append((addr, local_block_len, nixl_agent_meta.device_id))
+
+            if kv_topo.is_kv_layout_blocks_first:
+                second_split = self.get_backend_aware_kv_block_len(
+                    layer_idx=i, first_split=False, mamba_view=False
+                )
+                if tp_ratio < 0 and not self.use_mla:
+                    second_split = second_split // transfer_cfg.physical_fa_num_reads
+                for block_id in range(num_blocks):
+                    block_offset = block_id * page_size
+                    addr = base_addr + block_offset + rank_offset
+                    v_addr = addr + nixl_agent_meta.block_lens[i] // 2
+                    result.append((v_addr, second_split, nixl_agent_meta.device_id))
+        return result
+
+    def _build_mamba_remote(
+        self,
+        nixl_agent_meta: NixlAgentMetadata,
+        tp_ratio: int,
+    ) -> list[tuple[int, int, int]]:
+        """Build 4 remote desc regions (x, B, C, ssm) per layer for
+        the 3-read transfer.  For hetero-TP, each D rank reads only its
+        sub-projection slice from the P rank."""
+        assert self._conv_decomp is not None
+        effective_ratio = max(tp_ratio, 1)
+        # Mamba conv state is always TP-sharded, even when attention KV
+        # is replicated (num_kv_heads < tp_size).
+        local_offset = self.tp_rank % effective_ratio
+        conv_size_remote = nixl_agent_meta.ssm_sizes[0]
+
+        if tp_ratio >= 1:
+            # D_TP >= P_TP: P page is larger, D reads its slice.
+            conv_offsets = self._conv_decomp.remote_conv_offsets(
+                local_offset, effective_ratio
+            )
+            ssm_read_size = self._mamba_ssm_size[1]
+        else:
+            # NOTE (ZhanqiuHu): tp_ratio < 0 means P_TP > D_TP, so P pages
+            # are smaller than D's.  self._conv_decomp has D-sized dimensions,
+            # but we need P-sized offsets.  Scale down by |tp_ratio|.
+            abs_ratio = -tp_ratio
+            xb_p = self._conv_decomp.x_bytes // abs_ratio
+            bb_p = self._conv_decomp.b_bytes // abs_ratio
+            conv_offsets = [(0, xb_p), (xb_p, bb_p), (xb_p + bb_p, bb_p)]
+            ssm_read_size = nixl_agent_meta.ssm_sizes[1]
+
+        remote_ratio = self._mamba_phys_ratio[nixl_agent_meta.engine_id]
+        num_blocks = nixl_agent_meta.num_blocks // remote_ratio
+        device_id = nixl_agent_meta.device_id
+
+        result: list[tuple[int, int, int]] = []
+        # NOTE (ZhanqiuHu): use per-layer block_lens[i], not [0], in case
+        # block lengths vary across layers (e.g. MLA).
+        for i, base_addr in enumerate(nixl_agent_meta.kv_caches_base_addr):
+            page_stride = nixl_agent_meta.block_lens[i] * remote_ratio
+            for off, sz in conv_offsets:
+                for blk in range(num_blocks):
+                    result.append((base_addr + blk * page_stride + off, sz, device_id))
+            # SSM temporal state is also TP-sharded on the heads dimension.
+            for blk in range(num_blocks):
+                ssm_addr = (
+                    base_addr
+                    + blk * page_stride
+                    + conv_size_remote
+                    + local_offset * ssm_read_size
+                )
+                result.append((ssm_addr, ssm_read_size, device_id))
+        return result
+
     def register_local_xfer_handler(
         self,
         block_size: int,
@@ -1823,13 +1996,22 @@ class NixlConnectorWorker:
                 self.device_id,
             )
 
+        # NOTE (ZhanqiuHu): mamba=True path in register_blocks is not used
+        # right now — we use _build_mamba_local instead for the 3-read
+        # approach. However, we might still need this as a fallback for homogeneous TP.
         register_blocks(blocks_data, mamba=False)
         if self._has_mamba:
             assert self.num_descs == len(blocks_data)
-            logger.debug(
-                "Registering additional %s local Mamba blocks", len(blocks_data)
+            # TODO (ZhanqiuHu): For homogeneous TP (tp_ratio == 1), the 3-read split is
+            # unnecessary — a single conv desc per block suffices.  Consider
+            # adding a fast path that falls back to the standard 2-region
+            # registration (register_blocks mamba=True) when no hetero-TP
+            # remote has been seen.  Currently we always register 4 regions
+            # because local descs are created before knowing the remote TP.
+            logger.debug("Registering local Mamba descriptors (4 regions/layer)")
+            blocks_data.extend(
+                self._build_mamba_local(local_base_addresses, block_size_ratio)
             )
-            register_blocks(blocks_data, mamba=True)
 
         descs = self.nixl_wrapper.get_xfer_descs(blocks_data, self.nixl_memory_type)
         # NIXL_INIT_AGENT to be used for preparations of local descs.
@@ -1880,6 +2062,9 @@ class NixlConnectorWorker:
 
         Regarding MLA case, the cache is replicated across TP workers so the rank_offset will just always be 0
         so that the whole cache is shared by "tp_ratio" D TP workers.
+
+        For Mamba hetero-TP, both tp_ratio > 0 (D_TP > P_TP) and
+        tp_ratio < 0 (P_TP > D_TP) are supported by the 3-read transfer.
         """  # noqa: E501
         engine_id = nixl_agent_meta.engine_id
         # TODO re-evaluate refreshing for scaling/recovery
@@ -1915,6 +2100,10 @@ class NixlConnectorWorker:
 
         if engine_id not in self.dst_num_blocks:
             self.dst_num_blocks[engine_id] = nixl_agent_meta.num_blocks
+        if self._has_mamba:
+            self._mamba_phys_ratio[engine_id] = compute_mamba_phys_ratio(
+                nixl_agent_meta.ssm_sizes, nixl_agent_meta.block_lens[0]
+            )
 
         # Keep track of remote agent kv caches base addresses.
         self.kv_caches_base_addr[engine_id][remote_tp_rank] = (
@@ -1931,6 +2120,21 @@ class NixlConnectorWorker:
             not self.kv_topo.replicates_kv_cache(engine_id) and tp_ratio > 0
         )
 
+        # Create transfer config (single source of truth for descriptor sizes).
+        if self._has_mamba and engine_id not in self._transfer_configs:
+            self._transfer_configs[engine_id] = HeteroTPTransferConfig(
+                tp_ratio=tp_ratio,
+                K=kv_topo.total_num_kv_heads,
+                d_tp=self.world_size,
+                p_tp=remote_tp_size,
+                d_rank=self.tp_rank,
+                use_mla=self.use_mla,
+                d_block_len=self.block_len_per_layer[0],
+                p_block_len=nixl_agent_meta.block_lens[0],
+                is_blocks_first=kv_topo.is_kv_layout_blocks_first,
+            )
+            logger.info("Created %s", self._transfer_configs[engine_id].describe())
+
         logger.debug(
             "Registering remote agent (%s, rank %s) memory regions with tp_ratio %s",
             engine_id,
@@ -1947,21 +2151,48 @@ class NixlConnectorWorker:
             # Remote tp_size > local tp_size: read from multiple remote ranks.
             # Logically "split" own regions into |tp_ratio| chunks. Mind that
             # we only do this once per remote tp_size (replica-friendly).
+            abs_tp = -tp_ratio
             self.src_xfer_handles_by_tp_ratio[tp_ratio] = []
-            for i in range(-tp_ratio):
-                blocks_data = []
-                for memory_region in self.src_blocks_data:
-                    addr, local_block_len, own_tp_rank = memory_region
-                    # Computing block len layer by layer allows for different
-                    # block sizes to be used.
-                    remote_block_len = local_block_len // (-tp_ratio)
-                    addr = addr + i * remote_block_len
-                    blocks_data.append((addr, remote_block_len, own_tp_rank))
-                descs = self.nixl_wrapper.get_xfer_descs(
-                    blocks_data, self.nixl_memory_type
-                )
-                handle = self.nixl_wrapper.prep_xfer_dlist("NIXL_INIT_AGENT", descs)
-                self.src_xfer_handles_by_tp_ratio[tp_ratio].append(handle)
+
+            if self._has_mamba:
+                transfer_cfg = self._transfer_configs.get(engine_id)
+                assert transfer_cfg is not None
+                if transfer_cfg.needs_split_handles:
+                    # Mamba-HMA: FA and Mamba use different split factors.
+                    for handle_data in transfer_cfg.compute_split_handle_data(
+                        self.src_blocks_data, self.num_descs, abs_tp
+                    ):
+                        descs = self.nixl_wrapper.get_xfer_descs(
+                            handle_data, self.nixl_memory_type
+                        )
+                        handle = self.nixl_wrapper.prep_xfer_dlist(
+                            "NIXL_INIT_AGENT", descs
+                        )
+                        self.src_xfer_handles_by_tp_ratio[tp_ratio].append(handle)
+
+                    logger.info(
+                        "Mamba-HMA split handles: targets=%s, fa_reads=%s, "
+                        "fa_entry=%s, mamba_reads=%s, num_descs=%s",
+                        transfer_cfg.transfer_targets,
+                        transfer_cfg.physical_fa_num_reads,
+                        transfer_cfg.fa_entry_size,
+                        transfer_cfg.mamba_num_reads,
+                        self.num_descs,
+                    )
+            else:
+                # Original path: uniform divide by abs_tp (non-Mamba-HMA).
+                for i in range(abs_tp):
+                    blocks_data = []
+                    for memory_region in self.src_blocks_data:
+                        addr, local_block_len, own_tp_rank = memory_region
+                        remote_block_len = local_block_len // abs_tp
+                        addr = addr + i * remote_block_len
+                        blocks_data.append((addr, remote_block_len, own_tp_rank))
+                    descs = self.nixl_wrapper.get_xfer_descs(
+                        blocks_data, self.nixl_memory_type
+                    )
+                    handle = self.nixl_wrapper.prep_xfer_dlist("NIXL_INIT_AGENT", descs)
+                    self.src_xfer_handles_by_tp_ratio[tp_ratio].append(handle)
 
         ### Register remote agent memory regions
         blocks_data = []
@@ -2044,13 +2275,33 @@ class NixlConnectorWorker:
                 self.tp_rank,
             )
 
-        register_remote_blocks(blocks_data, mamba=False)
         if self._has_mamba:
-            # Create extra descs for the Mamba "view" of the same KV cache tensors.
+            # Mamba-HMA: separate FA registration with GQA-aware sizing,
+            # plus mamba 3-read registration for the Mamba "view" of the
+            # same KV cache tensors.
             logger.debug(
-                "Registering additional %s remote Mamba blocks", len(blocks_data)
+                "Registering remote Mamba blocks for engine %s rank %s",
+                engine_id,
+                remote_tp_rank,
             )
-            register_remote_blocks(blocks_data, mamba=True)
+            transfer_cfg = self._transfer_configs.get(engine_id)
+            assert transfer_cfg is not None
+            blocks_data.extend(
+                self._build_fa_remote_for_mamba(
+                    nixl_agent_meta,
+                    transfer_cfg,
+                    block_size_ratio,
+                    kv_topo,
+                )
+            )
+            blocks_data.extend(
+                self._build_mamba_remote(
+                    nixl_agent_meta,
+                    tp_ratio,
+                )
+            )
+        else:
+            register_remote_blocks(blocks_data, mamba=False)
 
         # Register with NIXL.
         descs = self.nixl_wrapper.get_xfer_descs(blocks_data, self.nixl_memory_type)
@@ -2083,17 +2334,17 @@ class NixlConnectorWorker:
         block_size_ratio = self.kv_topo.block_size_ratio_from_engine_id(
             remote_engine_id
         )
-        # Num kv_heads > tp_size and P TP > D TP case, not supported
-        assert not (tp_ratio < 0 and self.kv_topo.is_kv_replicated(remote_engine_id))
+        # num_kv_heads > tp_size with P_TP > D_TP not supported for non-mamba.
+        # Mamba models can have replicated FA KV with tp_ratio < 0.
+        if not self._has_mamba:
+            assert not (
+                tp_ratio < 0 and self.kv_topo.is_kv_replicated(remote_engine_id)
+            )
 
         if self._is_hma_required:
             assert block_size_ratio == 1, (
                 "HMA does not support different remote block size yet"
             )
-        # Mamba additional constraints
-        if self._has_mamba:
-            assert tp_ratio == 1, "Mamba does not support heterogeneous TP yet"
-
         kv_cache_layout = (
             self.kv_cache_layout
             if not self.use_host_buffer
@@ -2138,11 +2389,14 @@ class NixlConnectorWorker:
         remote_block_len = nixl_agent_meta.block_lens[0]
         if self.use_mla or self.kv_topo.is_kv_replicated(remote_engine_id):
             # With replicated KV cache, only the number of blocks can differ.
-            for i in range(len(self.block_len_per_layer)):
-                assert (
-                    self.block_len_per_layer[i] // block_size_ratio
-                    == nixl_agent_meta.block_lens[i]
-                ), "KV cache sizes must match between P and D when replicated"
+            # TODO (ZhanqiuHu): For mamba models, validate FA and mamba
+            # block_lens separately.
+            if not self._has_mamba:
+                for i in range(len(self.block_len_per_layer)):
+                    assert (
+                        self.block_len_per_layer[i] // block_size_ratio
+                        == nixl_agent_meta.block_lens[i]
+                    ), "KV cache sizes must match between P and D when replicated"
         else:
             # When MLA is not used, this is a list of the same block length
             for block_len in nixl_agent_meta.block_lens:
@@ -2150,25 +2404,31 @@ class NixlConnectorWorker:
                     "All remote layers must have the same block size"
                 )
 
-            if tp_ratio > 0:
-                # Remote tp is smaller: remote block_len size is bigger
-                assert (
-                    remote_block_len
-                    == (self.block_len_per_layer[0] * tp_ratio) // block_size_ratio
-                ), (
-                    "Remote P worker KV layer cache must be of shape [2, N, "
-                    "local_kv_heads*tp_ratio, page_size, head_dim] and same dtype."
-                )  # noqa: E501
-            else:
-                assert block_size_ratio == 1, (
-                    "Different local/remote block sizes are not supported when"
-                    " P TP > D TP."
-                )
-                # Remote tp is bigger: remote block_len size is smaller
-                assert remote_block_len == self.block_len_per_layer[0] // (-tp_ratio), (
-                    "Remote P worker KV layer cache must be of shape [2, N, "
-                    "local_kv_heads/tp_ratio, page_size, head_dim] and same dtype."
-                )  # noqa: E501
+            # HMA hybrid models (mamba+attention) pad block_len to
+            # max(attn_page, mamba_page), so the linear tp_ratio scaling
+            # assumption only holds for pure-attention models.
+            if not self._has_mamba:
+                if tp_ratio > 0:
+                    assert (
+                        remote_block_len
+                        == (self.block_len_per_layer[0] * tp_ratio) // block_size_ratio
+                    ), (
+                        "Remote P worker KV layer cache must be of shape [2, N,"
+                        " local_kv_heads*tp_ratio, page_size, head_dim] and "
+                        "same dtype."
+                    )
+                else:
+                    assert block_size_ratio == 1, (
+                        "Different local/remote block sizes are not supported"
+                        " when P TP > D TP."
+                    )
+                    assert remote_block_len == self.block_len_per_layer[0] // (
+                        -tp_ratio
+                    ), (
+                        "Remote P worker KV layer cache must be of shape [2, N,"
+                        " local_kv_heads/tp_ratio, page_size, head_dim] and "
+                        "same dtype."
+                    )
 
         # TP workers that handhshake with same remote have same #blocks.
         assert self.dst_num_blocks[remote_engine_id] == nixl_agent_meta.num_blocks
@@ -2471,9 +2731,8 @@ class NixlConnectorWorker:
                 meta.local_block_ids
             )
             assert meta.remote is not None
-            meta.remote.block_ids = self._logical_to_kernel_block_ids(
-                meta.remote.block_ids
-            )
+            # Remote block IDs are kept logical here; expanded in
+            # _read_blocks_for_req using the remote engine's phys ratio.
             remote_engine_id = meta.remote.engine_id
             logger.debug(
                 "start_load_kv for request %s from remote engine %s. "
@@ -2525,6 +2784,13 @@ class NixlConnectorWorker:
             meta.remote.engine_id
         )
         tp_ratio = self.kv_topo.tp_ratio_from_engine_id(meta.remote.engine_id)
+
+        if self._has_mamba:
+            # Expand remote logical → kernel block IDs.
+            meta.remote.block_ids = self._logical_to_remote_kernel_block_ids(
+                meta.remote.block_ids,
+                self._mamba_phys_ratio[meta.remote.engine_id],
+            )
         # D may have to perform multiple reads from different remote ranks.
         for i, remote_rank in enumerate(remote_ranks):
             if self.use_mla and tp_ratio < 0 and i > 0:
@@ -2558,12 +2824,26 @@ class NixlConnectorWorker:
             remote_xfer_side_handle = self.dst_xfer_side_handles[meta.remote.engine_id][
                 remote_rank
             ]
+
+            local_ids: BlockIds = meta.local_physical_block_ids
+            remote_ids: BlockIds = meta.remote.block_ids
+            if self._has_mamba:
+                # Mamba-HMA: zero out FA groups for P ranks outside fa_read_targets.
+                transfer_cfg = self._transfer_configs.get(meta.remote.engine_id)
+                assert transfer_cfg is not None
+                local_ids, remote_ids = transfer_cfg.filter_block_ids_for_rank(
+                    remote_rank,
+                    local_ids,
+                    remote_ids,
+                    self._is_mamba_group,
+                )
+
             self._read_blocks(
                 request_id=req_id,
                 dst_engine_id=meta.remote.engine_id,
                 remote_request_id=meta.remote.request_id,
-                local_block_ids=meta.local_physical_block_ids,
-                remote_block_ids=meta.remote.block_ids,
+                local_block_ids=local_ids,
+                remote_block_ids=remote_ids,
                 remote_rank=remote_rank,
                 local_xfer_side_handle=local_xfer_side_handle,
                 remote_xfer_side_handle=remote_xfer_side_handle,
@@ -2663,9 +2943,12 @@ class NixlConnectorWorker:
         for i, remote_group in enumerate(remote_block_ids):
             num_remote_blocks = len(remote_group)
             num_local_blocks = len(local_block_ids[i])
-            assert num_local_blocks <= num_remote_blocks
+            if not self._is_mamba_group[i]:
+                assert num_local_blocks <= num_remote_blocks
             # Partial prefix cache hit: just read uncomputed blocks.
-            if num_local_blocks < num_remote_blocks:
+            # Skip mamba groups — their blocks represent full state (conv+ssm),
+            # not per-token data, so trimming would corrupt the transfer.
+            if num_local_blocks < num_remote_blocks and not self._is_mamba_group[i]:
                 remote_block_ids[i] = remote_group[-num_local_blocks:]
 
         # NOTE (nicolo) With homogeneous TP, each TP worker loads KV from
@@ -2781,16 +3064,22 @@ class NixlConnectorWorker:
             # This is like having two "low-level views" of the same storage.
             # `num_fa_descs` offset must be computed per-engine since P and D can
             # have different num_blocks (and thus different FA descs counts).
-            ratio = self._physical_blocks_per_logical_kv_block
-            # SSM may register fewer num_blocks than FA
+            ratio = self._mamba_phys_ratio[engine_id]
             logical_blocks = num_blocks // ratio
             num_fa_descs = self.num_regions * num_blocks
+            # 3-read mamba: 4 regions per unique cache tensor (x, B, C, ssm).
+            mamba_region_ids = np.arange(len(self.block_len_per_layer) * 4)[:, None]
             all_descs = []
             for i, group in enumerate(block_ids):
-                stride = logical_blocks if self._is_mamba_group[i] else num_blocks
                 group_arr = np.asarray(group)[None, :]
-                offset = num_fa_descs if self._is_mamba_group[i] else 0
-                all_descs.append((region_ids * stride + group_arr + offset).flatten())
+                if self._is_mamba_group[i]:
+                    all_descs.append(
+                        (
+                            mamba_region_ids * logical_blocks + group_arr + num_fa_descs
+                        ).flatten()
+                    )
+                else:
+                    all_descs.append((region_ids * num_blocks + group_arr).flatten())
             return np.concatenate(all_descs)
 
     def _logical_to_kernel_block_ids(self, block_ids: BlockIds) -> BlockIds:
@@ -2818,6 +3107,36 @@ class NixlConnectorWorker:
             for i, group in enumerate(block_ids)
         ]
 
+    def _logical_to_remote_kernel_block_ids(
+        self, block_ids: BlockIds, remote_ratio: int
+    ) -> BlockIds:
+        """Map logical block IDs to physical kernel block IDs on the remote.
+
+        Args:
+            block_ids: per-group lists of logical block IDs.
+            remote_ratio: remote engine's physical blocks per logical block.
+
+        Returns:
+            Same structure with FA groups expanded (each logical block L
+            becomes kernel blocks [L*remote_ratio .. L*remote_ratio +
+            local_ratio - 1]).  Mamba groups are passed through unchanged.
+        """
+        local_ratio = self._physical_blocks_per_logical_kv_block
+        if remote_ratio == 1:
+            return block_ids
+        local_arange = np.arange(local_ratio).reshape(1, -1)
+        group_specs = self.kv_cache_config.kv_cache_groups
+        result: list[list[int]] = []
+        for i, group in enumerate(block_ids):
+            if not isinstance(group_specs[i].kv_cache_spec, MambaSpec):
+                arr = np.array(group).reshape(-1, 1)
+                expanded = (arr * remote_ratio + local_arange).flatten()
+                result.append(expanded.tolist())
+            else:
+                # Mamba blocks are 1:1 logical-to-physical (no expansion).
+                result.append(group)
+        return result
+
     def get_backend_aware_kv_block_len(
         self, layer_idx: int, first_split: bool = True, mamba_view: bool = False
     ) -> int:

vllm/distributed/kv_transfer/kv_connector/v1/ssm_conv_transfer_utils.py

@@ -0,0 +1,164 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Mamba conv-state sub-projection decomposition for the 3-read transfer.
+
+With DS conv state layout (dim, state_len), x/B/C sub-projections are
+contiguous in memory.  Each D rank reads its x, B, C slices via 3
+separate RDMA transfers — no P-side permutation needed.
+"""
+
+import math
+from dataclasses import dataclass
+
+import torch
+
+from vllm.model_executor.layers.mamba.mamba_utils import is_conv_state_dim_first
+from vllm.v1.kv_cache_interface import MambaSpec
+
+
+@dataclass(frozen=True)
+class MambaConvSplitInfo:
+    """Per-rank byte sizes of x, B, C sub-projections in the Mamba conv state.
+
+    Used by both P and D sides for NIXL descriptor registration.
+    All fields are LOCAL to this engine's TP (already divided by TP size).
+
+    DS memory layout within one page (contiguous in memory):
+        |--- x (x_local * conv_rows) ---|- B (b_local * conv_rows) -|- C -|
+    """
+
+    conv_rows: int  # conv_kernel - 1 (typically 3)
+    x_local: int  # intermediate_size / TP  (columns for x)
+    b_local: int  # groups_ss / TP  (columns for B; C is same size)
+    conv_dtype_size: int  # bytes per element (e.g. 2 for float16)
+
+    @property
+    def conv_dim_local(self) -> int:
+        """Total conv columns per rank: x + B + C."""
+        return self.x_local + 2 * self.b_local
+
+    @property
+    def x_bytes(self) -> int:
+        """Byte size of the x sub-projection for one rank."""
+        return self.x_local * self.conv_rows * self.conv_dtype_size
+
+    @property
+    def b_bytes(self) -> int:
+        """Byte size of the B (or C) sub-projection for one rank."""
+        return self.b_local * self.conv_rows * self.conv_dtype_size
+
+    @property
+    def local_conv_offsets(self) -> list[tuple[int, int]]:
+        """(byte_offset, byte_size) of x, B, C within this engine's page.
+
+        Used by both P and D for local descriptor registration.
+        """
+        xb = self.x_bytes
+        bb = self.b_bytes
+        return [(0, xb), (xb, bb), (xb + bb, bb)]
+
+    def remote_conv_offsets(
+        self, local_rank_offset: int, tp_ratio: int
+    ) -> list[tuple[int, int]]:
+        """(byte_offset, byte_size) of this D rank's x, B, C slice within
+        one P page.
+
+        Used by D side only, during remote descriptor registration.
+
+        Args:
+            local_rank_offset: which slice this D rank reads.
+                tp_ratio > 0: tp_rank % tp_ratio (selects slice of P's page).
+                tp_ratio < 0: always 0 (read P's full page).
+            tp_ratio: effective ratio (>= 1 when D_TP > P_TP, 1 when
+                P_TP > D_TP since each P rank is read in full).
+        """
+        xb = self.x_bytes
+        bb = self.b_bytes
+        xr = xb * tp_ratio  # full remote x section in bytes
+        br = bb * tp_ratio  # full remote B section in bytes
+        return [
+            (local_rank_offset * xb, xb),
+            (xr + local_rank_offset * bb, bb),
+            (xr + br + local_rank_offset * bb, bb),
+        ]
+
+
+def derive_mamba_conv_split(
+    mamba_spec: MambaSpec,
+    local_tp: int,
+) -> MambaConvSplitInfo:
+    """Derive per-rank x/B/C byte sizes from a MambaSpec.
+
+    Called once at init on both P and D.  Decomposes the conv dimension
+    (= intermediate_size + 2 * groups_ss) into its x, B, C parts.
+
+    Args:
+        mamba_spec: MambaSpec whose shapes are:
+            shapes[0] = conv state: (conv_dim_local, conv_rows) in DS layout.
+            shapes[1] = SSM temporal: (local_num_heads, head_dim).
+        local_tp: this engine's tensor-parallel size.
+
+    Returns:
+        MambaConvSplitInfo with per-rank x_local, b_local, conv_rows, and
+        conv_dtype_size.
+    """
+    if mamba_spec.mamba_type != "mamba2":
+        raise NotImplementedError(
+            f"3-read conv transfer only supports Mamba2 models, "
+            f"got mamba_type={mamba_spec.mamba_type!r}.  "
+            f"Mamba1 SSM temporal shape is (intermediate_size // tp, state_size) "
+            f"which cannot be used to reconstruct intermediate_size."
+        )
+
+    conv_shape = mamba_spec.shapes[0]
+    assert len(conv_shape) == 2, f"Expected 2D conv state shape, got {conv_shape}"
+
+    # NOTE (ZhanqiuHu): 3-read requires DS layout, which is already asserted
+    # in nixl_connector __init__.  Use it directly instead of heuristic detection.
+    assert is_conv_state_dim_first(), "3-read requires DS conv state layout"
+    local_conv_dim = conv_shape[0]  # DS: (conv_dim_local, conv_rows)
+    conv_rows = conv_shape[1]
+
+    # NOTE (ZhanqiuHu): intermediate_size (= global x dim) is not stored
+    # in MambaSpec, so we reconstruct it from the SSM temporal state shape:
+    #   shapes[1] = (local_num_heads, head_dim), already divided by TP.
+    head_dim = mamba_spec.shapes[1][1]
+    local_num_heads = mamba_spec.shapes[1][0]
+    intermediate_size = local_num_heads * local_tp * head_dim
+
+    # NOTE (ZhanqiuHu): global conv dim = intermediate_size + 2 * groups_ss,
+    # where groups_ss is the B (= C) dimension.  B and C are always the same
+    # size, so we recover groups_ss from the remainder after subtracting x.
+    remainder = local_conv_dim * local_tp - intermediate_size
+    assert remainder > 0 and remainder % 2 == 0, (
+        f"Conv dim ({local_conv_dim}*tp={local_tp}) doesn't decompose into "
+        f"intermediate_size={intermediate_size} + 2*groups_ss. "
+        f"remainder={remainder}"
+    )
+    groups_ss = remainder // 2
+
+    conv_dtype_size = torch.tensor(
+        [],
+        dtype=mamba_spec.dtypes[0],  # type: ignore[misc]
+    ).element_size()
+
+    # Divide by TP to get per-rank column counts.
+    return MambaConvSplitInfo(
+        conv_rows=conv_rows,
+        x_local=intermediate_size // local_tp,
+        b_local=groups_ss // local_tp,
+        conv_dtype_size=conv_dtype_size,
+    )
+
+
+def compute_mamba_phys_ratio(ssm_sizes: tuple[int, ...], block_len: int) -> int:
+    """Derive _physical_blocks_per_logical_kv_block from remote metadata.
+
+    The remote engine's ratio is not sent directly in the handshake, so we
+    reconstruct it: total mamba state per logical block / block_len.
+
+    Args:
+        ssm_sizes: (conv_state_bytes, ssm_state_bytes) from NixlAgentMetadata.
+        block_len: the engine's block_len in bytes (from block_lens[0]).
+    """
+    return math.ceil((ssm_sizes[0] + ssm_sizes[1]) / block_len)