From 73b83949f76bfb806f3beca1be11b1dfb120145a Mon Sep 17 00:00:00 2001
From: wangxiyuan <wangxiyuan1007@gmail.com>
Date: Fri, 14 Aug 2026 03:25:07 +0800
Subject: [PATCH] [Platform] Add check_runner_kv_caches_multi_layer (#51633)

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>
---
 vllm/platforms/cpu.py       |  4 ++++
 vllm/platforms/cuda.py      |  4 ++++
 vllm/platforms/interface.py | 17 +++++++++++++++++
 vllm/platforms/rocm.py      |  4 ++++
 vllm/platforms/xpu.py       |  4 ++++
 vllm/v1/worker/utils.py     | 12 +-----------
 6 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/vllm/platforms/cpu.py b/vllm/platforms/cpu.py
index 4eeb98a79c..5633e160cc 100644
--- a/vllm/platforms/cpu.py
+++ b/vllm/platforms/cpu.py
@@ -70,6 +70,10 @@ class CpuPlatform(Platform):
         # x86/aarch64 CPU has supported both bf16 and fp16 natively.
         return [torch.bfloat16, torch.float16, torch.float32]
 
+    @classmethod
+    def check_runner_kv_caches_multi_layer(cls) -> None:
+        pass
+
     @classmethod
     def get_device_name(cls, device_id: int = 0) -> str:
         return "cpu"
diff --git a/vllm/platforms/cuda.py b/vllm/platforms/cuda.py
index aaaccfae75..bfe08a5772 100644
--- a/vllm/platforms/cuda.py
+++ b/vllm/platforms/cuda.py
@@ -229,6 +229,10 @@ class CudaPlatformBase(Platform):
         with contextlib.suppress(ImportError):
             import vllm._qutlass_C  # noqa: F401
 
+    @classmethod
+    def check_runner_kv_caches_multi_layer(cls) -> None:
+        pass
+
     @property
     def supported_dtypes(self) -> list[torch.dtype]:
         if self.has_device_capability(80):
diff --git a/vllm/platforms/interface.py b/vllm/platforms/interface.py
index f0b93da292..6781a9a86e 100644
--- a/vllm/platforms/interface.py
+++ b/vllm/platforms/interface.py
@@ -1200,6 +1200,23 @@ class Platform:
         """
         return False
 
+    @classmethod
+    def check_runner_kv_caches_multi_layer(cls) -> None:
+        """
+        Check whether the platform's ModelRunner can handle multiple attention
+        layers that share the same layer index (e.g. cross attention and self
+        attention in the same decoder block of an encoder-decoder model such as
+        BART).
+
+        Platforms that have verified that their ``runner_kv_caches`` is not
+        impacted by this case should override this to a no-op. Otherwise the
+        default implementation raises ``NotImplementedError``.
+        """
+        raise NotImplementedError(
+            "Multiple attention layers with the same layer index are not "
+            "supported on the current platform."
+        )
+
     @classmethod
     def support_deep_gemm(cls) -> bool:
         """
diff --git a/vllm/platforms/rocm.py b/vllm/platforms/rocm.py
index d7045a7431..9072c71426 100644
--- a/vllm/platforms/rocm.py
+++ b/vllm/platforms/rocm.py
@@ -547,6 +547,10 @@ class RocmPlatform(Platform):
         with contextlib.suppress(ImportError):
             import vllm._rocm_C  # noqa: F401
 
+    @classmethod
+    def check_runner_kv_caches_multi_layer(cls) -> None:
+        pass
+
     @classmethod
     def is_pin_memory_available(cls) -> bool:
         if in_wsl():
diff --git a/vllm/platforms/xpu.py b/vllm/platforms/xpu.py
index dde7a223f7..ddfde22522 100644
--- a/vllm/platforms/xpu.py
+++ b/vllm/platforms/xpu.py
@@ -134,6 +134,10 @@ class XPUPlatform(Platform):
         with contextlib.suppress(ImportError):
             import vllm._moe_C  # noqa: F401
 
+    @classmethod
+    def check_runner_kv_caches_multi_layer(cls) -> None:
+        pass
+
     @classmethod
     def get_attn_backend_cls(
         cls,
diff --git a/vllm/v1/worker/utils.py b/vllm/v1/worker/utils.py
index 46a73935df..d8f36b1d15 100644
--- a/vllm/v1/worker/utils.py
+++ b/vllm/v1/worker/utils.py
@@ -538,17 +538,7 @@ def bind_kv_cache(
             # TODO - analyze where runner_kv_caches is used and the right
             # way to ensure it properly reflects multiple attention layers
             # in the same decoder block.
-            if (
-                current_platform.is_cuda_alike()
-                or current_platform.is_xpu()
-                or current_platform.is_cpu()
-            ):
-                # We know that the GPU / CPU runner is not impacted by this
-                # case. Some test code depends on runner_kv_caches, but
-                # not in a way that's impacted by ignoring this.
-                pass
-            else:
-                raise NotImplementedError
+            current_platform.check_runner_kv_caches_multi_layer()
         for layer_name in layer_names:
             runner_kv_caches.append(kv_caches[layer_name])