Simplify flashinfer dispatch (#1552)

python/sglang/srt/model_executor/model_runner.py

@@ -231,6 +231,7 @@ class ModelRunner:
             if hasattr(self.model, "get_attention_sliding_window_size")
             else None
         )
+        self.has_cross_attention = getattr(self.model, "has_cross_attention", False)
         self.is_generation = is_generation_model(
             self.model_config.hf_config.architectures, self.server_args.is_embedding
         )
@@ -453,6 +454,10 @@ class ModelRunner:
                 "Window attention is not supported in the triton attention backend. "
                 "Please use `--attention-backend flashinfer`."
             )
+            assert not self.has_cross_attention, (
+                "Cross attention is not supported in the triton attention backend. "
+                "Please use `--attention-backend flashinfer`."
+            )
             self.attn_backend = TritonAttnBackend(self)
         else:
             raise ValueError(