[bugfix] Fixed an accuracy problem of gdn layer in graph (#6822)

### What this PR does / why we need it?

There will be random ouputs if we run model with GDN attention in graph
mode:

```python
prompts = [
    "1. Who are you?",
]
sampling_params = SamplingParams(temperature=0.6, top_p=0.95, top_k=40, max_tokens=32)
sampling_params = SamplingParams(temperature=0.0, top_p=0.95, top_k=40, max_tokens=5)
llm = LLM(model="/home/model/Qwen3-Next-80B-A3B-Instruct",
            tensor_parallel_size=4,

            distributed_executor_backend="mp",
            gpu_memory_utilization=0.7,
            speculative_config={
                "method": "qwen3_next_mtp",
                "num_speculative_tokens": 3,
            },
            
            compilation_config={
                "cudagraph_mode": "FULL_DECODE_ONLY",
                "cudagraph_capture_sizes": [8],
            },
            
            max_model_len=4096, 
            enable_prefix_caching=False)

outputs = llm.generate(prompts, sampling_params)
for output in outputs:
    prompt = output.prompt
    generated_text = output.outputs[0].text
    print(f"{output.prompt_token_ids=}")
    print(f"{output.outputs[0].token_ids=}")
    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
```

Before appling this change, the outputs was:

```text
output.prompt_token_ids=[16, 13, 10479, 525, 498, 30]
output.outputs[0].token_ids=[3555, 323, 279, 1112, 279]
Prompt: '1. Who are you?', Generated text: ' What and the... the'
```

After applying this change, the output is:

```text
output.prompt_token_ids=[16, 13, 10479, 525, 498, 30]
output.outputs[0].token_ids=[3555, 374, 697, 829, 30]
Prompt: '1. Who are you?', Generated text: ' What is your name?'
```

**Why does this change sovle the problem?**

Now, `query_start_loc` is padded because of `fia`.

But, for `gdn-attention`, padded version of `query_start_loc` will cause
accuracy problem.

So, we need an unpadded version of `query_start_loc` named
`gdn_query_start_loc` and use it in `gdn-attention`, it works fine.

### Does this PR introduce _any_ user-facing change?

N/A

### How was this patch tested?

As described aboved.

- vLLM version: v0.15.0
- vLLM main:
83b47f67b1

Signed-off-by: drslark <slarksblood@qq.com>

vllm_ascend/utils.py

@@ -1116,3 +1116,22 @@ def enable_dsa_cp_with_layer_shard() -> bool:
     vllm_config = get_current_vllm_config()
     is_prefill_instance = vllm_config.kv_transfer_config is not None and vllm_config.kv_transfer_config.is_kv_producer
     return is_prefill_instance
+
+
+def check_gdn_layer(vllm_config) -> bool:
+    """
+    gdn layer is marked with `linear_attention`.
+    So, if `linear_attention` is detected, we think the model has gdn-attention.
+    """
+    if not hasattr(vllm_config, "model_config"):
+        return False
+
+    model_config = vllm_config.model_config
+    if not hasattr(model_config, "hf_config"):
+        return False
+
+    hf_config = model_config.hf_config
+    if not hasattr(hf_config, "layer_types"):
+        return False
+
+    return "linear_attention" in hf_config.layer_types

vllm_ascend/worker/model_runner_v1.py

@@ -112,6 +112,7 @@ from vllm_ascend.spec_decode.eagle_proposer import EagleProposer
 from vllm_ascend.spec_decode.medusa_proposer import MedusaProposer
 from vllm_ascend.spec_decode.mtp_proposer import MtpProposer
 from vllm_ascend.utils import (
+    check_gdn_layer,
     enable_flash_comm_v1,
     enable_sp,
     is_drafter_moe_model,
@@ -229,6 +230,17 @@ class NPUModelRunner(GPUModelRunner):
             dtype=torch.int32,
         )
 
+        # Now, query_start_loc is padded.
+        # But gdn needs an unpadded one.
+        # gdn_query_start_loc is an unpadded version of query_start_loc.
+        # TODO delete it if fia's check is removed.
+        self._has_gdn = check_gdn_layer(vllm_config)
+        if self._has_gdn:
+            self.gdn_query_start_loc = self._make_buffer(
+                self.max_num_reqs + 1,  # type: ignore[has-type]
+                dtype=torch.int32,
+            )
+
         vllm_config.scheduler_config.max_num_batched_tokens -= max_pcp_pad_tokens
         self.max_num_tokens = self.scheduler_config.max_num_batched_tokens
         self.max_num_reqs = self.scheduler_config.max_num_seqs
@@ -677,6 +689,16 @@ class NPUModelRunner(GPUModelRunner):
         self.query_start_loc.np[1 : num_reqs + 1] = cu_num_tokens
         self.query_start_loc.copy_to_gpu()
 
+        # Now, query_start_loc is padded.
+        # But gdn needs an unpadded one.
+        # gdn_query_start_loc is an unpadded version of query_start_loc.
+        # TODO delete it if fia's check is removed.
+        if self._has_gdn:
+            self.gdn_query_start_loc.np[0] = 0
+            self.gdn_query_start_loc.np[1 : num_reqs + 1] = cu_num_tokens
+            self.gdn_query_start_loc.np[num_reqs + 1 :].fill(cu_num_tokens[-1])
+            self.gdn_query_start_loc.copy_to_gpu()
+
         self.seq_lens.np[:num_reqs] = self.input_batch.num_computed_tokens_cpu[:num_reqs] + num_scheduled_tokens
         self.seq_lens.copy_to_gpu()
 
@@ -2019,6 +2041,18 @@ class NPUModelRunner(GPUModelRunner):
                 kv_cache_group.kv_cache_spec,
                 num_reqs_padded,
             )
+
+            # Now, query_start_loc is padded.
+            # But gdn needs an unpadded one.
+            # gdn_query_start_loc is an unpadded version of query_start_loc.
+            # TODO delete it if fia's check is removed.
+            if self._has_gdn:
+                attn_group = self.attn_groups[kv_cache_gid][0]
+                builder = attn_group.get_metadata_builder(0)
+                if use_spec_decode and isinstance(builder, GDNAttentionMetadataBuilder):
+                    cm.query_start_loc_cpu = self.gdn_query_start_loc.cpu[: num_reqs_padded + 1]
+                    cm.query_start_loc = self.gdn_query_start_loc.gpu[: num_reqs_padded + 1]
+
             if kv_cache_gid > 0:
                 cm.block_table_tensor, cm.slot_mapping = _get_block_table_and_slot_mapping(kv_cache_gid)
             if self.speculative_config and spec_decode_common_attn_metadata is None: