diff --git a/tests/v1/attention/test_kpool_indexer_block_sizes.py b/tests/v1/attention/test_kpool_indexer_block_sizes.py
new file mode 100644
index 000000000000..a737988dde66
--- /dev/null
+++ b/tests/v1/attention/test_kpool_indexer_block_sizes.py
@@ -0,0 +1,135 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""CPU tests for storage-block kernel-block selection in prepare_kernel_block_sizes."""
+
+from types import SimpleNamespace
+
+import pytest
+import torch
+
+from vllm.config import VllmConfig, set_current_vllm_config
+from vllm.models.glm5next.common.attention import Glm5NextIndexerCache
+from vllm.v1.attention.backend import AttentionBackend, MultipleOf
+from vllm.v1.attention.backends.mla import indexer as indexer_mod
+from vllm.v1.attention.backends.mla.indexer import (
+    DeepseekV32IndexerBackend,
+    KpoolTailBackend,
+)
+from vllm.v1.attention.backends.mla.rocm_aiter_mla_sparse import (
+    ROCMAiterMLASparseBackend,
+)
+from vllm.v1.kv_cache_interface import MLAAttentionSpec
+from vllm.v1.worker.utils import prepare_kernel_block_sizes
+
+pytestmark = pytest.mark.cpu_test
+
+# ``index_kpool`` of zai-org/GLM-5.3-Flash: one indexer state pools 4
+# compressed states (hence storage_block_size = page * 4).
+INDEX_KPOOL = 4
+
+# The hybrid KDA/mamba manager floors at TP8..TP1; 640 is the geometry of the
+# original report ("the 640-token block table").
+TP_FLOOR_MANAGER_BLOCKS = [640, 1152, 2176, 4352]
+
+
+def _mock_rocm_platform(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Platform predicates are mutually exclusive in production. Override both
+    # so these ROCm policy tests do not inherit CUDA capabilities from the CI
+    # host running them (same approach as test_deepseek_v4_rocm_adaptive).
+    monkeypatch.setattr(indexer_mod.current_platform, "is_cuda", lambda: False)
+    monkeypatch.setattr(indexer_mod.current_platform, "is_rocm", lambda: True)
+
+
+def _kpool_storage_spec(manager_block: int) -> MLAAttentionSpec:
+    """Real Glm5NextIndexerCache spec for the given cache block size."""
+    with set_current_vllm_config(VllmConfig()):
+        cache = Glm5NextIndexerCache(
+            head_dim=128,
+            dtype=torch.bfloat16,
+            prefix="model.layers.0.indexer.k_cache_probe",
+            cache_config=SimpleNamespace(block_size=manager_block),
+            index_kpool=INDEX_KPOOL,
+        )
+        spec = cache.get_kv_cache_spec(VllmConfig())
+    assert isinstance(spec, MLAAttentionSpec)
+    return spec
+
+
+def _prepare(
+    spec: MLAAttentionSpec, backends: list[type[AttentionBackend]]
+) -> list[int]:
+    kv_cache_config = SimpleNamespace(
+        kv_cache_groups=[SimpleNamespace(kv_cache_spec=spec)]
+    )
+    attn_groups = [[SimpleNamespace(backend=backend) for backend in backends]]
+    return prepare_kernel_block_sizes(kv_cache_config, attn_groups)
+
+
+@pytest.mark.parametrize("manager_block", TP_FLOOR_MANAGER_BLOCKS)
+def test_prepare_uses_storage_block_for_the_kpool_group(
+    monkeypatch: pytest.MonkeyPatch, manager_block: int
+):
+    """The bug: on ROCm, kpool groups must get 128/256 - not the 640-4352
+    manager block - as their kernel block size.
+
+    Manager-granular selection is what made the block table address manager
+    blocks while the kpool writer and the index-cache gather read pool pages,
+    aliasing every cache column past the request's row.
+    """
+    _mock_rocm_platform(monkeypatch)
+    spec = _kpool_storage_spec(manager_block)
+    expected_storage = 256 if manager_block % 256 == 0 else 128
+    assert spec.storage_block_size == expected_storage
+
+    selected = _prepare(
+        spec,
+        [ROCMAiterMLASparseBackend, DeepseekV32IndexerBackend, KpoolTailBackend],
+    )
+    assert selected == [expected_storage]
+    assert selected != [manager_block]
+    # The hybrid block-table split stays integral.
+    assert manager_block % selected[0] == 0
+
+
+def test_prepare_falls_back_when_storage_block_is_not_supported():
+    """No storage block, or a storage block the backends reject (e.g. the
+    CUDA indexer's exact ``[64]`` vs a 128-token storage block): selection is
+    `select_common_block_size`'s answer, unchanged from no-fix behavior.
+    """
+
+    class Fixed64Backend:
+        @staticmethod
+        def get_supported_kernel_block_sizes():
+            return [64]
+
+        @staticmethod
+        def get_name() -> str:
+            return "FIXED64"
+
+    # Storage block the group's backend does not accept -> backend vote (64).
+    spec = _kpool_storage_spec(640)
+    assert spec.storage_block_size == 128
+    assert _prepare(spec, [Fixed64Backend]) == [64]
+
+    # No storage block at all (any non-kpool MLA model) -> backend vote.
+    plain_spec = MLAAttentionSpec(
+        block_size=640,
+        num_kv_heads=1,
+        head_size=128,
+        dtype=torch.bfloat16,
+    )
+    assert plain_spec.storage_block_size is None
+    assert _prepare(plain_spec, [Fixed64Backend]) == [64]
+
+    # ...and with backends that accept the manager block, the manager wins,
+    # exactly as on main.
+    class AcceptAllBackend:
+        @staticmethod
+        def get_supported_kernel_block_sizes():
+            return [MultipleOf(1)]
+
+        @staticmethod
+        def get_name() -> str:
+            return "ACCEPTALL"
+
+    assert _prepare(plain_spec, [AcceptAllBackend]) == [640]
diff --git a/vllm/v1/worker/utils.py b/vllm/v1/worker/utils.py
index 422ba8885fd7..b61c4cebed18 100644
--- a/vllm/v1/worker/utils.py
+++ b/vllm/v1/worker/utils.py
@@ -327,6 +327,30 @@ def update_draft_decode_metadata(
         self.get_metadata_builder().update_draft_decode_metadata(metadata)
 
 
+def _block_size_is_supported(
+    backends: list[type[AttentionBackend]], block_size: int
+) -> bool:
+    """Check if the block size is supported by all backends.
+
+    An exact ``int`` declaration must match exactly; a ``MultipleOf``
+    declaration accepts any multiple of its base.
+    """
+    for backend in backends:
+        is_supported = False
+        for supported_size in backend.get_supported_kernel_block_sizes():
+            if isinstance(supported_size, int):
+                if block_size == supported_size:
+                    is_supported = True
+            elif isinstance(supported_size, MultipleOf):
+                if block_size % supported_size.base == 0:
+                    is_supported = True
+            else:
+                raise ValueError(f"Unknown supported size: {supported_size}")
+        if not is_supported:
+            return False
+    return True
+
+
 def select_common_block_size(
     kv_manager_block_size: int,
     backends: list[type[AttentionBackend]],
@@ -348,27 +372,7 @@ def select_common_block_size(
         ValueError: If no valid block size found.
 
     """
-
-    def block_size_is_supported(
-        backends: list[type[AttentionBackend]], block_size: int
-    ) -> bool:
-        """Check if the block size is supported by all backends."""
-        for backend in backends:
-            is_supported = False
-            for supported_size in backend.get_supported_kernel_block_sizes():
-                if isinstance(supported_size, int):
-                    if block_size == supported_size:
-                        is_supported = True
-                elif isinstance(supported_size, MultipleOf):
-                    if block_size % supported_size.base == 0:
-                        is_supported = True
-                else:
-                    raise ValueError(f"Unknown supported size: {supported_size}")
-            if not is_supported:
-                return False
-        return True
-
-    if block_size_is_supported(backends, kv_manager_block_size):
+    if _block_size_is_supported(backends, kv_manager_block_size):
         return kv_manager_block_size
 
     # MultipleOf constraints also accept the manager size if they accept a divisor.
@@ -381,7 +385,7 @@ def block_size_is_supported(
     }
 
     for size in sorted(candidates, reverse=True):
-        if block_size_is_supported(backends, size):
+        if _block_size_is_supported(backends, size):
             return size
     raise ValueError(
         f"No common block size for {kv_manager_block_size} ("
@@ -493,9 +497,24 @@ def prepare_kernel_block_sizes(
             # This is an attention backend that supports virtual block splitting.
             kv_manager_block_size = kv_cache_group.kv_cache_spec.block_size
             group_backends = [g.backend for g in attn_groups[kv_cache_gid]]
-            selected_kernel_size = select_common_block_size(
-                kv_manager_block_size, group_backends
+            storage_block_size = (
+                kv_cache_spec.storage_block_size
+                if isinstance(kv_cache_spec, MLAAttentionSpec)
+                else None
             )
+            if storage_block_size is not None and _block_size_is_supported(
+                group_backends, storage_block_size
+            ):
+                # Storage-block specs (e.g. the GLM-5.3-Flash kpool indexer
+                # cache) address the cache in pool pages, and every other
+                # consumer (cache views, metadata builders, hisparse) already
+                # uses storage_block_size as the kernel block. Fall back to the
+                # backend vote when the group's backends do not accept it.
+                selected_kernel_size = storage_block_size
+            else:
+                selected_kernel_size = select_common_block_size(
+                    kv_manager_block_size, group_backends
+                )
             kernel_block_sizes.append(selected_kernel_size)
         elif isinstance(kv_cache_spec, MambaSpec):
             # This is likely Mamba or other non-attention cache, no splitting.