[Bugfix] Fix illegal memory access in FP8 MoE kernel (vllm-project#6382)

vllm/model_executor/layers/fused_moe/fused_moe.py

@@ -492,12 +492,14 @@ def fused_experts(hidden_states: torch.Tensor,
         if tokens_in_chunk == 0:
             break
 
-        if tokens_in_chunk < CHUNK_SIZE:
-            # will only happen in the last chunk
+        if tokens_in_chunk < CHUNK_SIZE and chunk > 0:
+            # Adjust the intermediate cache size and config for the last
+            # chunk. Note that in most cases we only have one chunk
+            # so the cache size and config are already set correctly and
+            # do not need to be adjusted.
             intermediate_cache1 = intermediate_cache1[:tokens_in_chunk]
             intermediate_cache2 = intermediate_cache2[:tokens_in_chunk]
             intermediate_cache3 = intermediate_cache3[:tokens_in_chunk]
-            # reload config to get better performance on the last chunk
             config = get_config_func(tokens_in_chunk)
 
         curr_topk_ids = topk_ids[begin_chunk_idx:end_chunk_idx]