[Model] Fix Kimi-K3 MLA with disabled context parallelism (#50404)

Signed-off-by: Tasos Varoudis <varoudis@archtech.gr>
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Co-authored-by: Lucas Wilkinson <lwilkins@redhat.com>

vllm/models/kimi_k3/nvidia/mla.py

@@ -301,6 +301,11 @@ class MultiHeadLatentAttention(nn.Module, AttentionLayerBase):
             kv_b_proj=self.kv_b_proj,
             indexer=None,
         )
+        if getattr(self.impl, "dcp_world_size", -1) < 1:
+            # FlashAttention requires the cp_world_size is positive and the cp_rank
+            # is non negative; manually set here if not set by caller (-1 is unset)
+            self.impl.dcp_world_size = 1
+            self.impl.dcp_rank = 0
         self.q_pad_num_heads = getattr(self.impl, "q_pad_num_heads", None)
 
         vllm_config = get_current_vllm_config()