Use paged_attention_v1 for sliding window decode in rocm_aiter_fa (#34378)

Signed-off-by: Martin Yuan <myuan@meta.com>
Co-authored-by: Martin Yuan <myuan@meta.com>

vllm/v1/attention/backends/rocm_aiter_fa.py

@@ -1075,35 +1075,6 @@ class AiterFlashAttentionImpl(AttentionImpl):
                     assert not rocm_aiter_ops.is_shuffle_kv_cache_enabled(), (
                         "Sliding window with shuffle layout is not supported yet."
                     )
-                    from aiter.ops.triton.unified_attention import (
-                        unified_attention,
-                    )
-
-                    descale_shape = (
-                        attn_metadata.query_start_loc[:num_decodes].shape[0] - 1,
-                        key_cache.shape[2],
-                    )
-                    unified_attention(
-                        q=query[:num_decode_tokens],
-                        k=key_cache,
-                        v=value_cache,
-                        out=output[:num_decode_tokens],
-                        cu_seqlens_q=attn_metadata.query_start_loc[:num_decodes],
-                        max_seqlen_q=1,  # optimize this
-                        seqused_k=attn_metadata.seq_lens[:num_decodes],
-                        max_seqlen_k=attn_metadata.max_seq_len,
-                        softmax_scale=self.scale,
-                        causal=True,
-                        alibi_slopes=self.alibi_slopes,
-                        window_size=self.sliding_window,
-                        block_table=attn_metadata.block_table[:num_decodes],
-                        softcap=self.logits_soft_cap,
-                        q_descale=None,
-                        k_descale=layer._k_scale.expand(descale_shape),
-                        v_descale=layer._v_scale.expand(descale_shape),
-                    )
-                    return
-                assert attn_metadata.decode_metadata is not None
 
                 if rocm_aiter_ops.is_shuffle_kv_cache_enabled():
                     num_blocks, block_size, num_kv_heads, head_size = key_cache.shape
@@ -1172,6 +1143,8 @@ class AiterFlashAttentionImpl(AttentionImpl):
                         layer._v_scale,
                         None,
                         _PARTITION_SIZE_ROCM,
+                        1,
+                        self.sliding_window[0] + 1,
                     )
         else:
             raise NotImplementedError(