[Bugfix] Enforce DeepGEMM when using sparse_attn_indexer on CUDA (#34374)

Signed-off-by: mgoin <mgoin64@gmail.com>

vllm/model_executor/layers/sparse_attn_indexer.py

@@ -10,6 +10,7 @@ from vllm.logger import init_logger
 from vllm.model_executor.custom_op import CustomOp
 from vllm.platforms import current_platform
 from vllm.utils.deep_gemm import fp8_mqa_logits, fp8_paged_mqa_logits
+from vllm.utils.import_utils import has_deep_gemm
 from vllm.utils.torch_utils import direct_register_custom_op
 from vllm.v1.attention.backends.mla.indexer import (
     DeepseekV32IndexerMetadata,
@@ -277,6 +278,10 @@ class SparseAttnIndexer(CustomOp):
         self.max_model_len = max_model_len
         self.max_total_seq_len = max_total_seq_len
         self.topk_indices_buffer = topk_indices_buffer
+        if current_platform.is_cuda() and not has_deep_gemm():
+            raise RuntimeError(
+                "Sparse Attention Indexer CUDA op requires DeepGEMM to be installed."
+            )
 
     def forward_native(
         self,