Sync from v0.13

vllm/attention/utils/kv_sharing_utils.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+def validate_kv_sharing_target(
+    current_layer_name, target_layer_name, static_forward_context
+):
+    error_msg = (
+        f"Specified KV sharing target layer for {current_layer_name} "
+        f"is not valid: target layer {target_layer_name} "
+    )
+
+    if current_layer_name == target_layer_name:
+        raise ValueError(error_msg + "cannot be the same as the current layer.")
+
+    if target_layer_name not in static_forward_context:
+        from vllm.model_executor.models.utils import extract_layer_index
+
+        # If target layer name is not in the static fwd context, it means either
+        # a) the target layer does not come BEFORE the current layer, or
+        # b) the target layer is not an Attention layer that exists in the model
+        current_layer_idx = extract_layer_index(current_layer_name)
+        target_layer_idx = extract_layer_index(target_layer_name)
+        if current_layer_idx <= target_layer_idx:
+            raise ValueError(error_msg + "must come before the current layer.")
+        else:
+            raise ValueError(error_msg + "is not a valid Attention layer in the model.")
+
+    # Currently KV sharing is only supported between layers of the same type
+    target_layer_attn_type = static_forward_context[target_layer_name].attn_type
+    expected = static_forward_context[current_layer_name].attn_type
+    if target_layer_attn_type != expected:
+        raise ValueError(
+            error_msg + f"must be the same type as the current layer ({expected})."
+        )