[Attention] Update tests to remove deprecated env vars (#30563)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>

.buildkite/scripts/hardware_ci/run-xpu-test.sh

@@ -39,7 +39,7 @@ docker run \
     python3 examples/offline_inference/basic/generate.py --model facebook/opt-125m --block-size 64 --enforce-eager -tp 2 --distributed-executor-backend ray
     python3 examples/offline_inference/basic/generate.py --model facebook/opt-125m --block-size 64 --enforce-eager -tp 2 --distributed-executor-backend mp
     python3 examples/offline_inference/basic/generate.py --model Intel/Qwen2.5-0.5B-W4A16-G128-AutoRound-LLMC-TEST-ONLY --enforce-eager
-    VLLM_ATTENTION_BACKEND=TRITON_ATTN python3 examples/offline_inference/basic/generate.py --model facebook/opt-125m --block-size 64 --enforce-eager
+    python3 examples/offline_inference/basic/generate.py --model facebook/opt-125m --block-size 64 --enforce-eager --attention-backend=TRITON_ATTN
     cd tests
     pytest -v -s v1/core
     pytest -v -s v1/engine

tests/basic_correctness/test_basic_correctness.py

@@ -67,7 +67,6 @@ def _fix_prompt_embed_outputs(
 @pytest.mark.parametrize("model_executor", ["uni", "mp"])
 @pytest.mark.parametrize("enable_prompt_embeds", [True, False])
 def test_models(
-    monkeypatch: pytest.MonkeyPatch,
     hf_runner,
     model: str,
     backend: str,
@@ -77,48 +76,46 @@ def test_models(
     model_executor: str,
     enable_prompt_embeds: bool,
 ) -> None:
-    with monkeypatch.context() as m:
+    # 5042 tokens for gemma2
-        m.setenv("VLLM_ATTENTION_BACKEND", backend)
+    # gemma2 has alternating sliding window size of 4096
+    # we need a prompt with more than 4096 tokens to test the sliding window
+    prompt = (
+        "The following numbers of the sequence "
+        + ", ".join(str(i) for i in range(1024))
+        + " are:"
+    )
+    example_prompts = [prompt]
 
-        # 5042 tokens for gemma2
+    with hf_runner(model) as hf_model:
-        # gemma2 has alternating sliding window size of 4096
+        hf_outputs = hf_model.generate_greedy(example_prompts, max_tokens)
-        # we need a prompt with more than 4096 tokens to test the sliding window
+        if enable_prompt_embeds:
-        prompt = (
+            with torch.no_grad():
-            "The following numbers of the sequence "
+                prompt_embeds = hf_model.get_prompt_embeddings(example_prompts)
-            + ", ".join(str(i) for i in range(1024))
-            + " are:"
-        )
-        example_prompts = [prompt]
 
-        with hf_runner(model) as hf_model:
+    with VllmRunner(
-            hf_outputs = hf_model.generate_greedy(example_prompts, max_tokens)
+        model,
-            if enable_prompt_embeds:
+        max_model_len=8192,
-                with torch.no_grad():
+        enforce_eager=enforce_eager,
-                    prompt_embeds = hf_model.get_prompt_embeddings(example_prompts)
+        enable_prompt_embeds=enable_prompt_embeds,
+        gpu_memory_utilization=0.7,
+        async_scheduling=async_scheduling,
+        distributed_executor_backend=model_executor,
+        attention_config={"backend": backend},
+    ) as vllm_model:
+        if enable_prompt_embeds:
+            vllm_outputs = vllm_model.generate_greedy(prompt_embeds, max_tokens)
+            vllm_outputs = _fix_prompt_embed_outputs(
+                vllm_outputs, hf_model, example_prompts
+            )
+        else:
+            vllm_outputs = vllm_model.generate_greedy(example_prompts, max_tokens)
 
-        with VllmRunner(
+    check_outputs_equal(
-            model,
+        outputs_0_lst=hf_outputs,
-            max_model_len=8192,
+        outputs_1_lst=vllm_outputs,
-            enforce_eager=enforce_eager,
+        name_0="hf",
-            enable_prompt_embeds=enable_prompt_embeds,
+        name_1="vllm",
-            gpu_memory_utilization=0.7,
+    )
-            async_scheduling=async_scheduling,
-            distributed_executor_backend=model_executor,
-        ) as vllm_model:
-            if enable_prompt_embeds:
-                vllm_outputs = vllm_model.generate_greedy(prompt_embeds, max_tokens)
-                vllm_outputs = _fix_prompt_embed_outputs(
-                    vllm_outputs, hf_model, example_prompts
-                )
-            else:
-                vllm_outputs = vllm_model.generate_greedy(example_prompts, max_tokens)
-
-        check_outputs_equal(
-            outputs_0_lst=hf_outputs,
-            outputs_1_lst=vllm_outputs,
-            name_0="hf",
-            name_1="vllm",
-        )
 
 
 @multi_gpu_test(num_gpus=2)
@@ -161,12 +158,6 @@ def test_models_distributed(
         ):  # noqa
             pytest.skip("enable_prompt_embeds does not work with ray compiled dag.")
 
-        if attention_backend:
-            monkeypatch_context.setenv(
-                "VLLM_ATTENTION_BACKEND",
-                attention_backend,
-            )
-
         for k, v in extra_env.items():
             monkeypatch_context.setenv(k, v)
 
@@ -178,6 +169,7 @@ def test_models_distributed(
         # if we run HF first, the cuda initialization will be done and it
         # will hurt multiprocessing backend with fork method
         # (the default method).
+        attention_config = {"backend": attention_backend} if attention_backend else None
         with vllm_runner(
             model,
             dtype=dtype,
@@ -185,6 +177,7 @@ def test_models_distributed(
             distributed_executor_backend=distributed_executor_backend,
             enable_prompt_embeds=enable_prompt_embeds,
             gpu_memory_utilization=0.7,
+            attention_config=attention_config,
         ) as vllm_model:
             if enable_prompt_embeds:
                 with hf_runner(model, dtype=dtype) as hf_model:

tests/compile/distributed/test_fusions_e2e.py

@@ -208,7 +208,8 @@ def test_attn_quant(
     # To capture subprocess logs, we need to know whether spawn or fork is used.
     # Force spawn as it is more general.
     monkeypatch.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend.name)
+
+    model_kwargs["attention_config"] = {"backend": backend.name}
 
     compilation_config = CompilationConfig(
         # Testing properties
@@ -297,7 +298,8 @@ def test_tp2_attn_quant_allreduce_rmsnorm(
     # To capture subprocess logs, we need to know whether spawn or fork is used.
     # Force spawn as it is more general.
     monkeypatch.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend.name)
+
+    model_kwargs["attention_config"] = {"backend": backend.name}
 
     compilation_config = CompilationConfig(
         # Testing properties
@@ -409,7 +411,8 @@ def test_tp2_attn_quant_async_tp(
     # To capture subprocess logs, we need to know whether spawn or fork is used.
     # Force spawn as it is more general.
     monkeypatch.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend.name)
+
+    model_kwargs["attention_config"] = {"backend": backend.name}
 
     compilation_config = CompilationConfig(
         # Testing properties

tests/compile/fullgraph/test_basic_correctness.py

@@ -89,7 +89,6 @@ class TestSetting:
     ],
 )
 def test_compile_correctness(
-    monkeypatch: pytest.MonkeyPatch,
     test_setting: TestSetting,
 ):
     # this test is run under multiple suits, with different GPUs.
@@ -107,49 +106,48 @@ def test_compile_correctness(
             f"{cuda_device_count_stateless()}"
         )
 
-    with monkeypatch.context() as m:
+    final_args = [
-        m.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
+        *model_args,
-        final_args = [
+        "-pp",
-            *model_args,
+        str(pp_size),
-            "-pp",
+        "-tp",
-            str(pp_size),
+        str(tp_size),
-            "-tp",
+        "-cc.cudagraph_mode=none",
-            str(tp_size),
+        f"--attention-backend={attn_backend}",
-            "-cc.cudagraph_mode=none",
+    ]
-        ]
 
-        all_args: list[list[str]] = []
+    all_args: list[list[str]] = []
-        all_envs: list[dict[str, str] | None] = []
+    all_envs: list[dict[str, str] | None] = []
 
-        for comp_mode in [
+    for comp_mode in [
-            CompilationMode.STOCK_TORCH_COMPILE,
+        CompilationMode.STOCK_TORCH_COMPILE,
-            CompilationMode.DYNAMO_TRACE_ONCE,
+        CompilationMode.DYNAMO_TRACE_ONCE,
-            CompilationMode.VLLM_COMPILE,
+        CompilationMode.VLLM_COMPILE,
-        ]:
+    ]:
-            for mode in [CompilationMode.NONE, comp_mode]:
+        for mode in [CompilationMode.NONE, comp_mode]:
-                all_args.append(
+            all_args.append(
-                    final_args + [f"-cc.mode={mode.name}", "-cc.backend=inductor"]
+                final_args + [f"-cc.mode={mode.name}", "-cc.backend=inductor"]
-                )
-
-            # inductor will change the output, so we only compare if the output
-            # is close, not exactly the same.
-            compare_all_settings(
-                model,
-                all_args,
-                all_envs,
-                method=method if method != "generate" else "generate_close",
             )
-            all_envs.clear()
-            all_args.clear()
 
-        for mode in [
+        # inductor will change the output, so we only compare if the output
-            CompilationMode.NONE,
+        # is close, not exactly the same.
-            CompilationMode.STOCK_TORCH_COMPILE,
+        compare_all_settings(
-            CompilationMode.DYNAMO_TRACE_ONCE,
+            model,
-            CompilationMode.VLLM_COMPILE,
+            all_args,
-        ]:
+            all_envs,
-            all_args.append(final_args + [f"-cc.mode={mode.name}", "-cc.backend=eager"])
+            method=method if method != "generate" else "generate_close",
-            all_envs.append({})
+        )
-            all_envs.append({})
+        all_envs.clear()
+        all_args.clear()
 
-        compare_all_settings(model, all_args * 3, all_envs, method=method)
+    for mode in [
+        CompilationMode.NONE,
+        CompilationMode.STOCK_TORCH_COMPILE,
+        CompilationMode.DYNAMO_TRACE_ONCE,
+        CompilationMode.VLLM_COMPILE,
+    ]:
+        all_args.append(final_args + [f"-cc.mode={mode.name}", "-cc.backend=eager"])
+        all_envs.append({})
+        all_envs.append({})
+
+    compare_all_settings(model, all_args * 3, all_envs, method=method)

tests/compile/fullgraph/test_full_cudagraph.py

@@ -74,7 +74,6 @@ def llm_pair(request):
         # Force native sampler to avoid potential nondeterminism in FlashInfer
         # when per-request generators are not used in V1.
         "VLLM_USE_FLASHINFER_SAMPLER": "0",
-        **backend_config.env_vars,
     }
     with temporary_environ(env_vars):
         full = LLM(
@@ -170,16 +169,10 @@ class TestFullCUDAGraph:
 
 @pytest.mark.skipif(not current_platform.is_cuda(), reason="Skip if not cuda")
 def test_full_cudagraph_with_invalid_backend():
-    with (
+    # Flex_Attention is not supported with full cuda graph
-        temporary_environ(
+    with pytest.raises(RuntimeError):
-            {
-                "VLLM_ATTENTION_BACKEND": "FLEX_ATTENTION",
-                # Flex_Attention is not supported with full cuda graph
-            }
-        ),
-        pytest.raises(RuntimeError),
-    ):
         LLM(
             model="Qwen/Qwen2-1.5B-Instruct",
             compilation_config=CompilationConfig(cudagraph_mode="FULL"),
+            attention_config={"backend": "FLEX_ATTENTION"},
         )

tests/compile/fullgraph/test_full_graph.py

@@ -197,20 +197,19 @@ def test_custom_compile_config(
     ],
 )
 def test_fp8_kv_scale_compile(
-    monkeypatch: pytest.MonkeyPatch,
     compilation_mode: int,
     model: str,
     backend: AttentionBackendEnum | None,
 ):
-    if backend:
-        monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend.name)
-
     model_kwargs = {
         "quantization": "fp8",
         "kv_cache_dtype": "fp8_e4m3",
         "calculate_kv_scales": True,
         "max_model_len": 512,
     }
+    if backend:
+        model_kwargs["attention_config"] = {"backend": backend.name}
+
     run_model(compilation_mode, model, **model_kwargs)
 
 

tests/distributed/test_context_parallel.py

@@ -219,14 +219,12 @@ def _test_cp_gsm8k(
         ]
     )
 
-    server_env = {}
     if attn_backend:
-        server_env["VLLM_ATTENTION_BACKEND"] = attn_backend
+        server_args.append(f"--attention-backend={attn_backend}")
 
     with RemoteOpenAIServer(
         model_id,
         server_args,
-        env_dict=server_env,
         max_wait_seconds=720,
     ) as remote_server:
         host = f"http://{remote_server.host}"

tests/distributed/test_pp_cudagraph.py

@@ -20,23 +20,21 @@ from ..utils import compare_two_settings, create_new_process_for_each_test
 )
 @create_new_process_for_each_test()
 def test_pp_cudagraph(
-    monkeypatch: pytest.MonkeyPatch,
     PP_SIZE: int,
     MODEL_NAME: str,
     ATTN_BACKEND: LiteralString,
 ):
-    with monkeypatch.context() as m:
+    cudagraph_args = [
-        cudagraph_args = [
+        # use half precision for speed and memory savings in CI environment
-            # use half precision for speed and memory savings in CI environment
+        "--dtype",
-            "--dtype",
+        "float16",
-            "float16",
+        "--pipeline-parallel-size",
-            "--pipeline-parallel-size",
+        str(PP_SIZE),
-            str(PP_SIZE),
+        "--distributed-executor-backend",
-            "--distributed-executor-backend",
+        "mp",
-            "mp",
+        f"--attention-backend={ATTN_BACKEND}",
-        ]
+    ]
-        m.setenv("VLLM_ATTENTION_BACKEND", ATTN_BACKEND)
 
-        eager_args = cudagraph_args + ["--enforce-eager"]
+    eager_args = cudagraph_args + ["--enforce-eager"]
 
-        compare_two_settings(MODEL_NAME, eager_args, cudagraph_args)
+    compare_two_settings(MODEL_NAME, eager_args, cudagraph_args)

tests/engine/test_arg_utils.py

@@ -9,7 +9,7 @@ from typing import Annotated, Literal
 
 import pytest
 
-from vllm.config import CompilationConfig, config
+from vllm.config import AttentionConfig, CompilationConfig, config
 from vllm.engine.arg_utils import (
     EngineArgs,
     contains_type,
@@ -298,6 +298,139 @@ def test_compilation_config():
     )
 
 
+def test_attention_config():
+    from vllm.attention.backends.registry import AttentionBackendEnum
+
+    parser = EngineArgs.add_cli_args(FlexibleArgumentParser())
+
+    # default value
+    args = parser.parse_args([])
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    assert engine_args.attention_config == AttentionConfig()
+
+    # set backend via dot notation
+    args = parser.parse_args(["--attention-config.backend", "FLASH_ATTN"])
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    assert engine_args.attention_config.backend is not None
+    assert engine_args.attention_config.backend.name == "FLASH_ATTN"
+
+    # set backend via --attention-backend shorthand
+    args = parser.parse_args(["--attention-backend", "FLASHINFER"])
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    assert engine_args.attention_backend is not None
+    assert engine_args.attention_backend == "FLASHINFER"
+
+    # set all fields via dot notation
+    args = parser.parse_args(
+        [
+            "--attention-config.backend",
+            "FLASH_ATTN",
+            "--attention-config.flash_attn_version",
+            "3",
+            "--attention-config.use_prefill_decode_attention",
+            "true",
+            "--attention-config.flash_attn_max_num_splits_for_cuda_graph",
+            "16",
+            "--attention-config.use_cudnn_prefill",
+            "true",
+            "--attention-config.use_trtllm_ragged_deepseek_prefill",
+            "true",
+            "--attention-config.use_trtllm_attention",
+            "true",
+            "--attention-config.disable_flashinfer_prefill",
+            "true",
+            "--attention-config.disable_flashinfer_q_quantization",
+            "true",
+        ]
+    )
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    assert engine_args.attention_config.backend is not None
+    assert engine_args.attention_config.backend.name == "FLASH_ATTN"
+    assert engine_args.attention_config.flash_attn_version == 3
+    assert engine_args.attention_config.use_prefill_decode_attention is True
+    assert engine_args.attention_config.flash_attn_max_num_splits_for_cuda_graph == 16
+    assert engine_args.attention_config.use_cudnn_prefill is True
+    assert engine_args.attention_config.use_trtllm_ragged_deepseek_prefill is True
+    assert engine_args.attention_config.use_trtllm_attention is True
+    assert engine_args.attention_config.disable_flashinfer_prefill is True
+    assert engine_args.attention_config.disable_flashinfer_q_quantization is True
+
+    # set to string form of a dict with all fields
+    args = parser.parse_args(
+        [
+            "--attention-config="
+            '{"backend": "FLASHINFER", "flash_attn_version": 2, '
+            '"use_prefill_decode_attention": false, '
+            '"flash_attn_max_num_splits_for_cuda_graph": 8, '
+            '"use_cudnn_prefill": false, '
+            '"use_trtllm_ragged_deepseek_prefill": false, '
+            '"use_trtllm_attention": false, '
+            '"disable_flashinfer_prefill": false, '
+            '"disable_flashinfer_q_quantization": false}',
+        ]
+    )
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    assert engine_args.attention_config.backend is not None
+    assert engine_args.attention_config.backend.name == "FLASHINFER"
+    assert engine_args.attention_config.flash_attn_version == 2
+    assert engine_args.attention_config.use_prefill_decode_attention is False
+    assert engine_args.attention_config.flash_attn_max_num_splits_for_cuda_graph == 8
+    assert engine_args.attention_config.use_cudnn_prefill is False
+    assert engine_args.attention_config.use_trtllm_ragged_deepseek_prefill is False
+    assert engine_args.attention_config.use_trtllm_attention is False
+    assert engine_args.attention_config.disable_flashinfer_prefill is False
+    assert engine_args.attention_config.disable_flashinfer_q_quantization is False
+
+    # test --attention-backend flows into VllmConfig.attention_config
+    args = parser.parse_args(
+        [
+            "--model",
+            "facebook/opt-125m",
+            "--attention-backend",
+            "FLASH_ATTN",
+        ]
+    )
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    vllm_config = engine_args.create_engine_config()
+    assert vllm_config.attention_config.backend == AttentionBackendEnum.FLASH_ATTN
+
+    # test --attention-config.backend flows into VllmConfig.attention_config
+    args = parser.parse_args(
+        [
+            "--model",
+            "facebook/opt-125m",
+            "--attention-config.backend",
+            "FLASHINFER",
+        ]
+    )
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    vllm_config = engine_args.create_engine_config()
+    assert vllm_config.attention_config.backend == AttentionBackendEnum.FLASHINFER
+
+    # test --attention-backend and --attention-config.backend are mutually exclusive
+    args = parser.parse_args(
+        [
+            "--model",
+            "facebook/opt-125m",
+            "--attention-backend",
+            "FLASH_ATTN",
+            "--attention-config.backend",
+            "FLASHINFER",
+        ]
+    )
+    assert args is not None
+    engine_args = EngineArgs.from_cli_args(args)
+    with pytest.raises(ValueError, match="mutually exclusive"):
+        engine_args.create_engine_config()
+
+
 def test_prefix_cache_default():
     parser = EngineArgs.add_cli_args(FlexibleArgumentParser())
     args = parser.parse_args([])

tests/entrypoints/openai/test_serving_chat.py

@@ -76,15 +76,10 @@ def default_server_args(with_tool_parser: bool):
 
 
 @pytest.fixture(scope="module")
-def gptoss_server(
+def gptoss_server(default_server_args: list[str]):
-    monkeypatch_module: pytest.MonkeyPatch, default_server_args: list[str]
+    server_args = default_server_args + ["--attention-backend=TRITON_ATTN"]
-):
+    with RemoteOpenAIServer(GPT_OSS_MODEL_NAME, server_args) as remote_server:
-    with monkeypatch_module.context() as m:
+        yield remote_server
-        m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN")
-        with RemoteOpenAIServer(
-            GPT_OSS_MODEL_NAME, default_server_args
-        ) as remote_server:
-            yield remote_server
 
 
 @pytest_asyncio.fixture

tests/kernels/attention/test_attention_selector.py

@@ -6,7 +6,9 @@ from unittest.mock import patch
 import pytest
 import torch
 
+from vllm.attention.backends.registry import AttentionBackendEnum
 from vllm.attention.selector import _cached_get_attn_backend, get_attn_backend
+from vllm.config import AttentionConfig, VllmConfig, set_current_vllm_config
 from vllm.platforms import current_platform
 from vllm.platforms.cpu import CpuPlatform
 from vllm.platforms.cuda import CudaPlatform
@@ -73,18 +75,18 @@ def generate_params():
 
 
 @pytest.mark.parametrize("device, name, use_mla, block_size", generate_params())
-def test_env(
+def test_backend_selection(
     device: str,
     name: str,
     use_mla: bool,
     block_size: int,
-    monkeypatch: pytest.MonkeyPatch,
 ):
     """Test attention backend selection with valid device-backend pairs."""
-    with monkeypatch.context() as m:
+    # Create AttentionConfig with the specified backend
-        m.setenv("VLLM_ATTENTION_BACKEND", name)
+    attention_config = AttentionConfig(backend=AttentionBackendEnum[name])
-        m.setenv("VLLM_MLA_DISABLE", "1" if use_mla else "0")
+    vllm_config = VllmConfig(attention_config=attention_config)
 
+    with set_current_vllm_config(vllm_config):
         if device == "cpu":
             with patch("vllm.platforms.current_platform", CpuPlatform()):
                 backend = get_attn_backend(16, torch.float16, None, block_size)
@@ -217,27 +219,32 @@ def test_env(
 @pytest.mark.parametrize("device", ["cpu", "cuda"])
 def test_fp32_fallback(device: str):
     """Test attention backend selection with fp32."""
-    if device == "cpu":
+    # Use default config (no backend specified)
-        with patch("vllm.platforms.current_platform", CpuPlatform()):
+    vllm_config = VllmConfig()
-            backend = get_attn_backend(16, torch.float32, None, 16)
-        assert backend.get_name() == "CPU_ATTN"
 
-    elif device == "cuda":
+    with set_current_vllm_config(vllm_config):
-        with patch("vllm.platforms.current_platform", CudaPlatform()):
+        if device == "cpu":
-            backend = get_attn_backend(16, torch.float32, None, 16)
+            with patch("vllm.platforms.current_platform", CpuPlatform()):
-        assert backend.get_name() == "FLEX_ATTENTION"
+                backend = get_attn_backend(16, torch.float32, None, 16)
+            assert backend.get_name() == "CPU_ATTN"
+
+        elif device == "cuda":
+            with patch("vllm.platforms.current_platform", CudaPlatform()):
+                backend = get_attn_backend(16, torch.float32, None, 16)
+            assert backend.get_name() == "FLEX_ATTENTION"
 
 
 def test_flash_attn(monkeypatch: pytest.MonkeyPatch):
     """Test FlashAttn validation."""
     pytest.skip(
         "Skipping as current backend selector does not "
-        "handle fallbacks when a backend is set via env var."
+        "handle fallbacks when a backend is explicitly set."
     )
 
-    with monkeypatch.context() as m:
+    attention_config = AttentionConfig(backend=AttentionBackendEnum.FLASH_ATTN)
-        m.setenv("VLLM_ATTENTION_BACKEND", "FLASH_ATTN")
+    vllm_config = VllmConfig(attention_config=attention_config)
 
+    with set_current_vllm_config(vllm_config):
         # Unsupported CUDA arch
         monkeypatch.setattr(torch.cuda, "get_device_capability", lambda _=None: (7, 5))
         backend = get_attn_backend(16, torch.float16, None, 16)
@@ -277,15 +284,10 @@ def test_flash_attn(monkeypatch: pytest.MonkeyPatch):
         assert backend.get_name() != "FLASH_ATTN"
 
 
-def test_invalid_env(monkeypatch: pytest.MonkeyPatch):
+def test_invalid_backend():
     """Test that invalid attention backend names raise ValueError."""
     with (
-        monkeypatch.context() as m,
+        pytest.raises(ValueError),
-        patch("vllm.platforms.current_platform", CudaPlatform()),
     ):
-        m.setenv("VLLM_ATTENTION_BACKEND", "INVALID")
+        # Invalid backend name should raise ValueError when creating enum
-
+        AttentionConfig(backend=AttentionBackendEnum["INVALID"])
-        # Should raise ValueError for invalid backend
-        with pytest.raises(ValueError) as exc_info:
-            get_attn_backend(32, torch.float16, None, 16)
-        assert "Invalid value 'INVALID'" in str(exc_info.value)

tests/kernels/attention/test_rocm_attention_selector.py

@@ -4,7 +4,9 @@
 import pytest
 import torch
 
+from vllm.attention.backends.registry import AttentionBackendEnum
 from vllm.attention.selector import _cached_get_attn_backend, get_attn_backend
+from vllm.config import AttentionConfig, VllmConfig, set_current_vllm_config
 from vllm.platforms.rocm import RocmPlatform
 
 
@@ -16,40 +18,56 @@ def clear_cache():
 
 @pytest.mark.skip(reason="Skipped for now. Should be revisited.")
 def test_selector(monkeypatch: pytest.MonkeyPatch):
-    with monkeypatch.context() as m:
+    # Set the current platform to ROCm using monkeypatch
-        m.setenv("VLLM_ATTENTION_BACKEND", "ROCM_ATTN")
+    monkeypatch.setattr("vllm.attention.selector.current_platform", RocmPlatform())
 
-        # Set the current platform to ROCm using monkeypatch
+    # Test standard ROCm attention
-        monkeypatch.setattr("vllm.attention.selector.current_platform", RocmPlatform())
+    attention_config = AttentionConfig(backend=AttentionBackendEnum.ROCM_ATTN)
+    vllm_config = VllmConfig(attention_config=attention_config)
 
-        # Test standard ROCm attention
+    with set_current_vllm_config(vllm_config):
         backend = get_attn_backend(16, torch.float16, torch.float16, 16, False)
         assert backend.get_name() == "ROCM_FLASH" or backend.get_name() == "TRITON_ATTN"
 
-        # MLA test for deepseek related
+    # MLA test for deepseek related
+    # Change the attention backend to triton MLA
+    attention_config = AttentionConfig(backend=AttentionBackendEnum.TRITON_MLA)
+    vllm_config = VllmConfig(attention_config=attention_config)
 
-        # change the attention backend to triton MLA
+    with set_current_vllm_config(vllm_config):
-        m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_MLA")
         backend = get_attn_backend(576, torch.bfloat16, "auto", 16, False, use_mla=True)
         assert backend.get_name() == "TRITON_MLA"
 
-        # If attention backend is None
+    # If attention backend is None
-        # If use_mla is true
+    # If use_mla is true
-        # The selected backend is triton MLA
+    # The selected backend is triton MLA
-        m.setenv("VLLM_ATTENTION_BACKEND", "")
+    attention_config = AttentionConfig(backend=None)
+    vllm_config = VllmConfig(attention_config=attention_config)
+
+    with set_current_vllm_config(vllm_config):
         backend = get_attn_backend(576, torch.bfloat16, "auto", 16, False, use_mla=True)
         assert backend.get_name() == "TRITON_MLA"
 
-        # change the attention backend to AITER MLA
+    # Change the attention backend to AITER MLA
-        m.setenv("VLLM_ATTENTION_BACKEND", "ROCM_AITER_MLA")
+    attention_config = AttentionConfig(backend=AttentionBackendEnum.ROCM_AITER_MLA)
+    vllm_config = VllmConfig(attention_config=attention_config)
+
+    with set_current_vllm_config(vllm_config):
         backend = get_attn_backend(576, torch.bfloat16, "auto", 1, False, use_mla=True)
         assert backend.get_name() == "ROCM_AITER_MLA"
 
-        # If attention backend is None
+    # If attention backend is None
-        # If use_mla is true
+    # If use_mla is true
-        # If VLLM_ROCM_USE_AITER is enabled
+    # If VLLM_ROCM_USE_AITER is enabled
-        # The selected backend is ROCM_AITER_MLA
+    # The selected backend is ROCM_AITER_MLA
-        m.setenv("VLLM_ATTENTION_BACKEND", "")
+    with monkeypatch.context() as m:
         m.setenv("VLLM_ROCM_USE_AITER", "1")
-        backend = get_attn_backend(576, torch.bfloat16, "auto", 1, False, use_mla=True)
+
-        assert backend.get_name() == "ROCM_AITER_MLA"
+        attention_config = AttentionConfig(backend=None)
+        vllm_config = VllmConfig(attention_config=attention_config)
+
+        with set_current_vllm_config(vllm_config):
+            backend = get_attn_backend(
+                576, torch.bfloat16, "auto", 1, False, use_mla=True
+            )
+            assert backend.get_name() == "ROCM_AITER_MLA"

tests/kernels/test_flex_attention.py

@@ -37,7 +37,7 @@ def set_seed(seed):
     not torch.cuda.is_available() or TORCH_VERSION < MINIMUM_TORCH_VERSION,
     reason="CUDA not available or PyTorch version < 2.7",
 )
-def test_flex_attention_vs_default_backend(vllm_runner, monkeypatch):
+def test_flex_attention_vs_default_backend(vllm_runner):
     """Test that FlexAttention produces the same outputs as the default backend.
 
     This test compares the outputs from the FlexAttention backend with
@@ -54,35 +54,32 @@ def test_flex_attention_vs_default_backend(vllm_runner, monkeypatch):
     ]
 
     # Run with flex attention
-    with monkeypatch.context() as m:
+    set_seed(seed)
-        m.setenv("VLLM_ATTENTION_BACKEND", "FLEX_ATTENTION")
+    with vllm_runner(
-
+        model_name,
-        set_seed(seed)
+        runner="generate",
-        with vllm_runner(
+        tensor_parallel_size=1,
-            model_name,
+        num_gpu_blocks_override=128,
-            runner="generate",
+        enforce_eager=True,
-            tensor_parallel_size=1,
+        attention_config={"backend": "FLEX_ATTENTION"},
-            num_gpu_blocks_override=128,
+    ) as llm_flex:
-            enforce_eager=True,
+        output_flex = llm_flex.generate_greedy_logprobs(
-        ) as llm_flex:
+            prompts, max_tokens, num_logprobs
-            output_flex = llm_flex.generate_greedy_logprobs(
+        )
-                prompts, max_tokens, num_logprobs
-            )
 
     # Run with default backend
-    with monkeypatch.context() as m:
+    set_seed(seed)
-        set_seed(seed)
+    with vllm_runner(
-        with vllm_runner(
+        model_name,
-            model_name,
+        runner="generate",
-            runner="generate",
+        tensor_parallel_size=1,
-            tensor_parallel_size=1,
+        num_gpu_blocks_override=128,
-            num_gpu_blocks_override=128,
+        enforce_eager=True,
-            enforce_eager=True,
+        gpu_memory_utilization=0.85,
-            gpu_memory_utilization=0.85,
+    ) as llm_default:
-        ) as llm_default:
+        output_default = llm_default.generate_greedy_logprobs(
-            output_default = llm_default.generate_greedy_logprobs(
+            prompts, max_tokens, num_logprobs
-                prompts, max_tokens, num_logprobs
+        )
-            )
 
     check_logprobs_close(
         outputs_0_lst=output_flex,
@@ -96,7 +93,7 @@ def test_flex_attention_vs_default_backend(vllm_runner, monkeypatch):
     not torch.cuda.is_available() or TORCH_VERSION < MINIMUM_TORCH_VERSION,
     reason="CUDA not available or PyTorch version < 2.7",
 )
-def test_encoder_flex_attention_vs_default_backend(vllm_runner, monkeypatch):
+def test_encoder_flex_attention_vs_default_backend(vllm_runner):
     """Test that FlexAttention produces the same outputs as the default backend.
 
     This test compares the outputs from the FlexAttention backend with
@@ -110,30 +107,26 @@ def test_encoder_flex_attention_vs_default_backend(vllm_runner, monkeypatch):
     ]
 
     # Run with flex attention
-    with monkeypatch.context() as m:
+    with vllm_runner(
-        m.setenv("VLLM_ATTENTION_BACKEND", "FLEX_ATTENTION")
+        model_name,
-        with vllm_runner(
+        runner="pooling",
-            model_name,
+        dtype=torch.bfloat16,
-            runner="pooling",
+        tensor_parallel_size=1,
-            dtype=torch.bfloat16,
+        max_model_len=100,
-            tensor_parallel_size=1,
+        enforce_eager=True,
-            max_model_len=100,
+        attention_config={"backend": "FLEX_ATTENTION"},
-            enforce_eager=True,
+    ) as llm_flex:
-        ) as llm_flex:
+        flex_outputs = llm_flex.embed(prompts)
-            flex_outputs = llm_flex.embed(prompts)
 
     # Run with default backend
-    with (
+    with vllm_runner(
-        monkeypatch.context() as m,
+        model_name,
-        vllm_runner(
+        runner="pooling",
-            model_name,
+        dtype=torch.bfloat16,
-            runner="pooling",
+        tensor_parallel_size=1,
-            dtype=torch.bfloat16,
+        max_model_len=100,
-            tensor_parallel_size=1,
+        enforce_eager=True,
-            max_model_len=100,
+    ) as llm_default:
-            enforce_eager=True,
-        ) as llm_default,
-    ):
         default_outputs = llm_default.embed(prompts)
 
     check_embeddings_close(

tests/models/multimodal/generation/test_granite_speech.py

@@ -35,10 +35,12 @@ audio_lora_path = MODEL_NAME
 models = [MODEL_NAME]
 
 
-@pytest.fixture(autouse=True)
+@pytest.fixture
-def set_attention_backend_for_rocm(monkeypatch):
+def granite_speech_attention_config():
+    """Return attention config for Granite Speech tests on ROCm."""
     if current_platform.is_rocm():
-        monkeypatch.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN")
+        return {"backend": "TRITON_ATTN"}
+    return None
 
 
 def run_test(
@@ -53,6 +55,7 @@ def run_test(
     num_logprobs: int,
     tensor_parallel_size: int,
     distributed_executor_backend: str | None = None,
+    attention_config: dict | None = None,
 ):
     """Inference result should be the same between hf and vllm.
 
@@ -80,6 +83,7 @@ def run_test(
         enable_lora=True,
         max_lora_rank=64,
         enforce_eager=True,
+        attention_config=attention_config,
     ) as vllm_model:
         lora_request = LoRARequest("audio", 1, audio_lora_path)
         vllm_outputs_per_case = [
@@ -131,6 +135,7 @@ def test_models(
     vllm_runner,
     model: str,
     audio_assets: AudioTestAssets,
+    granite_speech_attention_config,
     dtype: str,
     max_model_len: int,
     max_tokens: int,
@@ -157,4 +162,5 @@ def test_models(
         max_tokens=max_tokens,
         num_logprobs=num_logprobs,
         tensor_parallel_size=1,
+        attention_config=granite_speech_attention_config,
     )

tests/models/multimodal/pooling/conftest.py

@@ -2,23 +2,17 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 """Pytest configuration for vLLM pooling tests."""
 
-import os
+import pytest
-import warnings
 
 from vllm.platforms import current_platform
 
 
-def pytest_collection_modifyitems(config, items):
+@pytest.fixture
-    """Set FLEX_ATTENTION backend for SigLIP tests on ROCm."""
+def siglip_attention_config():
-    if not current_platform.is_rocm():
+    """Return attention config for SigLIP tests on ROCm.
-        return
 
-    siglip_tests = [item for item in items if "test_siglip" in item.nodeid]
+    On ROCm, SigLIP tests require FLEX_ATTENTION backend.
-
+    """
-    if siglip_tests:
+    if current_platform.is_rocm():
-        os.environ["VLLM_ATTENTION_BACKEND"] = "FLEX_ATTENTION"
+        return {"backend": "FLEX_ATTENTION"}
-        warnings.warn(
+    return None
-            "ROCm: Set VLLM_ATTENTION_BACKEND=FLEX_ATTENTION for SigLIP tests",
-            UserWarning,
-            stacklevel=1,
-        )

tests/models/multimodal/pooling/test_siglip.py

@@ -38,6 +38,7 @@ def _run_test(
     *,
     dtype: str,
     tokenization_kwargs: dict[str, Any] | None = None,
+    attention_config: dict[str, Any] | None = None,
 ) -> None:
     if tokenization_kwargs is None:
         tokenization_kwargs = {}
@@ -49,6 +50,7 @@ def _run_test(
         enforce_eager=True,
         max_model_len=64,
         gpu_memory_utilization=0.7,
+        attention_config=attention_config,
     ) as vllm_model:
         vllm_outputs = vllm_model.embed(
             input_texts, images=input_images, tokenization_kwargs=tokenization_kwargs
@@ -90,6 +92,7 @@ def test_models_text(
     hf_runner,
     vllm_runner,
     image_assets,
+    siglip_attention_config,
     model: str,
     dtype: str,
 ) -> None:
@@ -108,6 +111,7 @@ def test_models_text(
             "padding": "max_length",
             "max_length": 64,
         },  # siglip2 was trained with this padding setting.
+        attention_config=siglip_attention_config,
     )
 
 
@@ -117,6 +121,7 @@ def test_models_image(
     hf_runner,
     vllm_runner,
     image_assets,
+    siglip_attention_config,
     model: str,
     dtype: str,
 ) -> None:
@@ -133,6 +138,7 @@ def test_models_image(
         input_images,
         model,
         dtype=dtype,
+        attention_config=siglip_attention_config,
     )
 
 
@@ -141,6 +147,7 @@ def test_models_image(
 def test_models_text_image_no_crash(
     vllm_runner,
     image_assets,
+    siglip_attention_config,
     model: str,
     dtype: str,
 ) -> None:
@@ -154,6 +161,7 @@ def test_models_text_image_no_crash(
         enforce_eager=True,
         max_model_len=64,
         gpu_memory_utilization=0.7,
+        attention_config=siglip_attention_config,
     ) as vllm_model:
         with pytest.raises(ValueError, match="not both"):
             vllm_model.embed(texts, images=images)

tests/models/quantization/test_fp8.py

@@ -75,7 +75,6 @@ def test_models(
 
     with monkeypatch.context() as m:
         m.setenv("TOKENIZERS_PARALLELISM", "true")
-        m.setenv("VLLM_ATTENTION_BACKEND", backend)
 
         MAX_MODEL_LEN = 1024
         NUM_LOG_PROBS = 8
@@ -86,6 +85,7 @@ def test_models(
             tensor_parallel_size=tensor_parallel_size,
             enforce_eager=enforce_eager,
             kv_cache_dtype="auto",
+            attention_config={"backend": backend},
         ) as vllm_model:
             baseline_outputs = vllm_model.generate_greedy_logprobs(
                 example_prompts, max_tokens, NUM_LOG_PROBS
@@ -97,6 +97,7 @@ def test_models(
             tensor_parallel_size=tensor_parallel_size,
             enforce_eager=enforce_eager,
             kv_cache_dtype=kv_cache_dtype,
+            attention_config={"backend": backend},
         ) as vllm_model:
             test_outputs = vllm_model.generate_greedy_logprobs(
                 example_prompts, max_tokens, NUM_LOG_PROBS

tests/models/test_initialization.py

@@ -108,11 +108,12 @@ def can_initialize(
         patch.object(V1EngineCore, "_initialize_kv_caches", _initialize_kv_caches_v1),
         monkeypatch.context() as m,
     ):
-        if model_arch == "GptOssForCausalLM":
+        # FIXME: A hack to bypass FA3 assertion because our CI's L4 GPU
-            # FIXME: A hack to bypass FA3 assertion because our CI's L4 GPU
+        # has cc==8.9 which hasn't supported FA3 yet. Remove this hack when
-            # has cc==8.9 which hasn't supported FA3 yet. Remove this hack when
+        # L4 supports FA3.
-            # L4 supports FA3.
+        attention_config = (
-            m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN")
+            {"backend": "TRITON_ATTN"} if model_arch == "GptOssForCausalLM" else None
+        )
         if model_arch == "WhisperForConditionalGeneration":
             m.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
 
@@ -143,6 +144,7 @@ def can_initialize(
             else "vllm",
             hf_overrides=hf_overrides_fn,
             max_num_seqs=model_info.max_num_seqs,
+            attention_config=attention_config,
         )
 
 

tests/v1/attention/test_rocm_attention_backends_selection.py

@@ -94,26 +94,20 @@ def mock_on_gfx9():
             None,
             AttentionBackendEnum.ROCM_AITER_UNIFIED_ATTN.get_path(),
         ),
-        # Test Case 9: VLLM_V1_USE_PREFILL_DECODE_ATTENTION=1
+        # Test Case 9: VLLM_ROCM_USE_AITER=1 + explicit TRITON_ATTN
-        (
-            {"VLLM_V1_USE_PREFILL_DECODE_ATTENTION": "1"},
-            None,
-            AttentionBackendEnum.ROCM_ATTN.get_path(),
-        ),
-        # Test Case 10: VLLM_ROCM_USE_AITER=1 + explicit TRITON_ATTN
         (
             {"VLLM_ROCM_USE_AITER": "1"},
             "TRITON_ATTN",
             AttentionBackendEnum.TRITON_ATTN.get_path(),
         ),
-        # Test Case 11: VLLM_ROCM_USE_AITER=1 + VLLM_ROCM_USE_AITER_MHA=0
+        # Test Case 10: VLLM_ROCM_USE_AITER=1 + VLLM_ROCM_USE_AITER_MHA=0
         # (explicitly disabled)
         (
             {"VLLM_ROCM_USE_AITER": "1", "VLLM_ROCM_USE_AITER_MHA": "0"},
             None,
             AttentionBackendEnum.TRITON_ATTN.get_path(),
         ),
-        # Test Case 12: VLLM_ROCM_USE_AITER=1 + explicit ROCM_ATTN
+        # Test Case 11: VLLM_ROCM_USE_AITER=1 + explicit ROCM_ATTN
         (
             {"VLLM_ROCM_USE_AITER": "1"},
             "ROCM_ATTN",

tests/v1/attention/utils.py

@@ -249,8 +249,8 @@ def create_dummy_kv_cache(
 @dataclass
 class BackendConfig:
     name: str
-    env_vars: dict
+    attention_config: dict
-    comp_config: dict  # compilation config
+    comp_config: dict
     specific_gpu_arch: tuple | None = None
 
 
@@ -259,10 +259,10 @@ full_cg_backend_configs = {
     # FA3 on Hopper
     "FA3": BackendConfig(
         name="FA3",
-        env_vars={
+        attention_config={
-            "VLLM_ATTENTION_BACKEND": "FLASH_ATTN",
+            "backend": "FLASH_ATTN",
-            "VLLM_FLASH_ATTN_VERSION": "3",
+            "flash_attn_version": 3,
-            "VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH": "16",
+            "flash_attn_max_num_splits_for_cuda_graph": 16,
         },
         comp_config={
             "cudagraph_mode": "FULL",
@@ -272,9 +272,7 @@ full_cg_backend_configs = {
     # FlashMLA on Hopper
     "FlashMLA": BackendConfig(
         name="FlashMLA",
-        env_vars={
+        attention_config={"backend": "FLASHMLA"},
-            "VLLM_ATTENTION_BACKEND": "FLASHMLA",
-        },
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
         },
@@ -283,9 +281,7 @@ full_cg_backend_configs = {
     # Cutlass MLA on Blackwell
     "CutlassMLA": BackendConfig(
         name="CutlassMLA",
-        env_vars={
+        attention_config={"backend": "CUTLASS_MLA"},
-            "VLLM_ATTENTION_BACKEND": "CUTLASS_MLA",
-        },
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
         },
@@ -294,9 +290,7 @@ full_cg_backend_configs = {
     # FlashInfer MLA on Blackwell
     "FlashInferMLA": BackendConfig(
         name="FlashInferMLA",
-        env_vars={
+        attention_config={"backend": "FLASHINFER_MLA"},
-            "VLLM_ATTENTION_BACKEND": "FLASHINFER_MLA",
-        },
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
         },
@@ -305,9 +299,9 @@ full_cg_backend_configs = {
     # FlashAttention MLA on Hopper
     "FlashAttentionMLA": BackendConfig(
         name="FlashAttentionMLA",
-        env_vars={
+        attention_config={
-            "VLLM_ATTENTION_BACKEND": "FLASH_ATTN_MLA",
+            "backend": "FLASH_ATTN_MLA",
-            "VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH": "16",
+            "flash_attn_max_num_splits_for_cuda_graph": 16,
         },
         comp_config={
             "cudagraph_mode": "FULL_DECODE_ONLY",
@@ -317,10 +311,10 @@ full_cg_backend_configs = {
     # FA2
     "FA2": BackendConfig(
         name="FA2",
-        env_vars={
+        attention_config={
-            "VLLM_ATTENTION_BACKEND": "FLASH_ATTN",
+            "backend": "FLASH_ATTN",
-            "VLLM_FLASH_ATTN_VERSION": "2",
+            "flash_attn_version": 2,
-            "VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH": "16",
+            "flash_attn_max_num_splits_for_cuda_graph": 16,
         },
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
@@ -329,7 +323,7 @@ full_cg_backend_configs = {
     # Triton Attention
     "TritonAttn": BackendConfig(
         name="TritonAttn",
-        env_vars={"VLLM_ATTENTION_BACKEND": "TRITON_ATTN"},
+        attention_config={"backend": "TRITON_ATTN"},
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
         },
@@ -337,14 +331,17 @@ full_cg_backend_configs = {
     # FlashInfer
     "FlashInfer": BackendConfig(
         name="FlashInfer",
-        env_vars={"VLLM_ATTENTION_BACKEND": "FLASHINFER"},
+        attention_config={"backend": "FLASHINFER"},
         comp_config={
             "cudagraph_mode": "FULL_AND_PIECEWISE",
         },
     ),
     "RocmAttn": BackendConfig(
         name="RocmAttn",
-        env_vars={"VLLM_V1_USE_PREFILL_DECODE_ATTENTION": "1"},
+        attention_config={
+            "backend": "ROCM_ATTN",
+            "use_prefill_decode_attention": True,
+        },
         comp_config={
             "cudagraph_mode": "FULL",
         },

tests/v1/cudagraph/test_cudagraph_mode.py

@@ -1,7 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-import contextlib
-import os
 import weakref
 from contextlib import ExitStack
 
@@ -13,26 +11,6 @@ from vllm import LLM
 from vllm.config import CompilationConfig, CompilationMode
 from vllm.platforms import current_platform
 
-
-@contextlib.contextmanager
-def temporary_environ(env_vars):
-    """
-    Temporarily set environment variables and restore them afterward.
-    We have to do this vs monkeypatch because monkeypatch doesn't work
-    with "module" scoped fixtures.
-    """
-    original_env = {k: os.environ.get(k) for k in env_vars}
-    try:
-        os.environ.update(env_vars)
-        yield
-    finally:
-        for k, v in original_env.items():
-            if v is None:
-                os.environ.pop(k, None)
-            else:
-                os.environ[k] = v
-
-
 # test attention backend and cudagraph_mode combo
 # (backend_name, cudagraph_mode, supported)
 if current_platform.is_rocm():
@@ -68,9 +46,9 @@ def test_backend_and_cudagraph_mode_combo(backend_name, cudagraph_mode, supporte
     ):
         pytest.skip("Only Hopper GPUs support FA3 and FlashMLA")
 
-    env_vars = backend_configs[backend_name].env_vars
+    attention_config = backend_config.attention_config
 
-    with temporary_environ(env_vars), ExitStack() as stack:
+    with ExitStack() as stack:
         if not supported:
             stack.enter_context(pytest.raises(Exception))
 
@@ -80,6 +58,7 @@ def test_backend_and_cudagraph_mode_combo(backend_name, cudagraph_mode, supporte
             trust_remote_code=True,
             gpu_memory_utilization=0.45,
             max_model_len=1024,
+            attention_config=attention_config,
             compilation_config=CompilationConfig(
                 mode=CompilationMode.VLLM_COMPILE, cudagraph_mode=cudagraph_mode
             ),
@@ -122,9 +101,10 @@ combo_cases_2 = [
 def test_cudagraph_compilation_combo(
     backend_name, cudagraph_mode, compilation_mode, supported
 ):
-    env_vars = backend_configs[backend_name].env_vars
+    backend_config = backend_configs[backend_name]
+    attention_config = backend_config.attention_config
 
-    with temporary_environ(env_vars), ExitStack() as stack:
+    with ExitStack() as stack:
         if not supported:
             stack.enter_context(pytest.raises(Exception))
 
@@ -134,6 +114,7 @@ def test_cudagraph_compilation_combo(
             trust_remote_code=True,
             gpu_memory_utilization=0.45,
             max_model_len=1024,
+            attention_config=attention_config,
             compilation_config=CompilationConfig(
                 mode=compilation_mode, cudagraph_mode=cudagraph_mode
             ),

tests/v1/determinism/test_batch_invariance.py

@@ -28,7 +28,7 @@ IS_DEVICE_CAPABILITY_BELOW_90 = is_device_capability_below_90()
     BACKENDS,
 )
 def test_v1_generation_is_deterministic_across_batch_sizes_with_needle(
-    backend, monkeypatch: pytest.MonkeyPatch
+    backend,
 ):
     """
     Ensures that the same request (the 'needle' prompt) yields identical output
@@ -54,7 +54,7 @@ def test_v1_generation_is_deterministic_across_batch_sizes_with_needle(
     seed = int(os.getenv("VLLM_TEST_SEED", "12345"))
     random.seed(seed)
 
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
+    attention_config = {"backend": backend}
     # Allow overrides from environment (useful for CI tuning)
     # "facebook/opt-125m" is too small, doesn't reliably test determinism
     model = resolve_model_name(backend)
@@ -92,6 +92,7 @@ def test_v1_generation_is_deterministic_across_batch_sizes_with_needle(
             max_num_seqs=max_batch_size,
             gpu_memory_utilization=gpu_mem_util,
             max_model_len=max_model_len,
+            attention_config=attention_config,
         )
 
         # Baseline generation for the needle prompt alone.
@@ -106,6 +107,7 @@ def test_v1_generation_is_deterministic_across_batch_sizes_with_needle(
             max_num_seqs=max_batch_size,
             gpu_memory_utilization=gpu_mem_util,
             max_model_len=max_model_len,
+            attention_config=attention_config,
         )
 
         mismatches = 0
@@ -163,10 +165,8 @@ def test_v1_generation_is_deterministic_across_batch_sizes_with_needle(
     BACKENDS,
 )
 def test_logprobs_bitwise_batch_invariance_bs1_vs_bsN(
-    backend, monkeypatch: pytest.MonkeyPatch
+    backend,
 ):
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
-
     seed = int(os.getenv("VLLM_TEST_SEED", "12345"))
     random.seed(seed)
     model_name = resolve_model_name(backend)
@@ -193,6 +193,7 @@ def test_logprobs_bitwise_batch_invariance_bs1_vs_bsN(
         dtype="bfloat16",  # not everything is supported
         gpu_memory_utilization=0.9,
         enforce_eager=IS_DEVICE_CAPABILITY_BELOW_90,
+        attention_config={"backend": backend},
     )
 
     # Use more realistic prompts for better token generation
@@ -381,12 +382,11 @@ def test_logprobs_bitwise_batch_invariance_bs1_vs_bsN(
     "backend",
     BACKENDS,
 )
-def test_simple_generation(backend, monkeypatch: pytest.MonkeyPatch):
+def test_simple_generation(backend):
     """
     Simple test that runs the model with a basic prompt and prints the output.
     Useful for quick smoke testing and debugging.
     """
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
     model = resolve_model_name(backend)
 
     llm = LLM(
@@ -398,6 +398,7 @@ def test_simple_generation(backend, monkeypatch: pytest.MonkeyPatch):
         dtype="bfloat16",
         enable_prefix_caching=False,
         enforce_eager=IS_DEVICE_CAPABILITY_BELOW_90,
+        attention_config={"backend": backend},
     )
 
     prompt = "the capital of france is"
@@ -444,8 +445,6 @@ def test_logprobs_without_batch_invariance_should_fail(
     The test will PASS if we detect differences (proving batch invariance matters).
     The test will FAIL if everything matches (suggesting batch invariance isn't needed).
     """
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
-
     # CRITICAL: Disable batch invariance for this test
     monkeypatch.setenv("VLLM_BATCH_INVARIANT", "0")
     monkeypatch.setattr(batch_invariant, "VLLM_BATCH_INVARIANT", False)
@@ -465,6 +464,7 @@ def test_logprobs_without_batch_invariance_should_fail(
         max_model_len=8192,
         dtype="bfloat16",
         enforce_eager=IS_DEVICE_CAPABILITY_BELOW_90,
+        attention_config={"backend": backend},
     )
 
     # build ragged prompts to change shapes significantly across BS=1 vs BS=N
@@ -649,7 +649,7 @@ def test_logprobs_without_batch_invariance_should_fail(
 @skip_unsupported
 @pytest.mark.parametrize("backend", ["FLASH_ATTN"])
 def test_decode_logprobs_match_prefill_logprobs(
-    backend, monkeypatch: pytest.MonkeyPatch
+    backend,
 ):
     """
     Test that verifies decode logprobs match prefill logprobs.
@@ -664,8 +664,6 @@ def test_decode_logprobs_match_prefill_logprobs(
     This ensures that the logprobs from decode are consistent with what
     we would get if we ran prefill on each prefix.
     """
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
-
     seed = int(os.getenv("VLLM_TEST_SEED", "12345"))
     random.seed(seed)
     model_name = resolve_model_name(backend)
@@ -689,6 +687,7 @@ def test_decode_logprobs_match_prefill_logprobs(
         max_model_len=8192,
         dtype="bfloat16",
         enforce_eager=IS_DEVICE_CAPABILITY_BELOW_90,
+        attention_config={"backend": backend},
     )
 
     # Use a few test prompts
@@ -920,6 +919,7 @@ def LLM_with_max_seqs(
     max_num_seqs: int,
     gpu_memory_utilization: float,
     max_model_len: int,
+    attention_config: dict | None = None,
 ) -> LLM:
     """
     Helper to construct an LLM with a specific max_num_seqs (batch-size limit)
@@ -934,6 +934,7 @@ def LLM_with_max_seqs(
         tensor_parallel_size=int(os.getenv("VLLM_TP_SIZE", "1")),
         enable_prefix_caching=False,
         enforce_eager=IS_DEVICE_CAPABILITY_BELOW_90,
+        attention_config=attention_config,
         # Enable for MOE models
         # enable_expert_parallel=True,
     )

tests/v1/determinism/test_online_batch_invariance.py

@@ -136,11 +136,9 @@ def _compare_bs1_vs_bsn_single_process(
 @skip_unsupported
 @pytest.mark.parametrize("backend", BACKENDS)
 def test_logprobs_bitwise_batch_invariance_bs1_vs_bsN(
-    backend: str, monkeypatch: pytest.MonkeyPatch
+    backend: str,
 ) -> None:
     random.seed(int(os.getenv("VLLM_TEST_SEED", "12345")))
-    # Override backend for this test (and the RemoteOpenAIServer child process).
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", backend)
     model_name = resolve_model_name(backend)
     prompts_all = [_random_prompt(10, 50) for _ in range(32)]
 
@@ -156,6 +154,7 @@ def test_logprobs_bitwise_batch_invariance_bs1_vs_bsN(
     server_args: list[str] = [
         "--max-model-len=8192",
         "--max-num-seqs=32",
+        f"--attention-backend={backend}",
     ]
     if tp_size:
         server_args += ["-tp", tp_size]

tests/v1/e2e/test_async_scheduling.py

@@ -142,16 +142,17 @@ def run_tests(
     """Test consistency of combos of async scheduling, preemption,
     uni/multiproc executor with spec decoding."""
 
-    with monkeypatch.context() as m:
+    # Determine attention config based on platform
-        # avoid precision errors
+    if current_platform.is_rocm():
-        if current_platform.is_rocm():
+        if is_testing_with_spec_decoding:
-            if is_testing_with_spec_decoding:
+            # Use TRITON_ATTN for spec decoding test for consistency
-                # Use TRITON_ATTN for spec decoding test for consistency
+            attention_config = {"backend": "TRITON_ATTN"}
-                m.setenv("VLLM_ATTENTION_BACKEND", "TRITON_ATTN")
-            else:
-                m.setenv("VLLM_ATTENTION_BACKEND", "ROCM_AITER_FA")
         else:
-            m.setenv("VLLM_ATTENTION_BACKEND", "FLEX_ATTENTION")
+            attention_config = {"backend": "ROCM_AITER_FA"}
+    else:
+        attention_config = {"backend": "FLEX_ATTENTION"}
+
+    with monkeypatch.context() as m:
         # lock matmul precision to full FP32 (IEEE)
         m.setenv("VLLM_FLOAT32_MATMUL_PRECISION", "ieee")
         # m.setenv("VLLM_BATCH_INVARIANT", "1")
@@ -174,6 +175,7 @@ def run_tests(
                 spec_config,
                 test_prefill_chunking=test_prefill_chunking,
                 is_testing_with_spec_decoding=is_testing_with_spec_decoding,
+                attention_config=attention_config,
             )
             outputs.append(test_results)
 
@@ -262,6 +264,7 @@ def run_test(
     spec_config: dict[str, Any] | None,
     test_prefill_chunking: bool,
     is_testing_with_spec_decoding: bool = False,
+    attention_config: dict[str, Any] | None = None,
 ):
     spec_decoding = spec_config is not None
     cache_arg: dict[str, Any] = (
@@ -301,6 +304,7 @@ def run_test(
         dtype=dtype,
         speculative_config=spec_config,
         disable_log_stats=False,
+        attention_config=attention_config,
         **cache_arg,
     ) as vllm_model:
         results = []

tests/v1/e2e/test_cascade_attention.py

@@ -10,7 +10,7 @@ from ...utils import create_new_process_for_each_test
 
 @create_new_process_for_each_test()
 @pytest.mark.parametrize("attn_backend", ["FLASH_ATTN", "FLASHINFER"])
-def test_cascade_attention(example_system_message, monkeypatch, attn_backend):
+def test_cascade_attention(example_system_message, attn_backend):
     prompt = "\n<User>: Implement fibonacci sequence in Python.\n<Claude>:"
 
     if attn_backend == "FLASHINFER":
@@ -19,19 +19,18 @@ def test_cascade_attention(example_system_message, monkeypatch, attn_backend):
             "needs investigation. See issue #25679."
         )
 
-    with monkeypatch.context() as m:
+    llm = LLM(
-        m.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
+        model="Qwen/Qwen2-1.5B-Instruct", attention_config={"backend": attn_backend}
+    )
+    sampling_params = SamplingParams(temperature=0.0, max_tokens=100)
 
-        llm = LLM(model="Qwen/Qwen2-1.5B-Instruct")
+    # No cascade attention.
-        sampling_params = SamplingParams(temperature=0.0, max_tokens=100)
+    single_prompt = [example_system_message + prompt]
+    responses = llm.generate(single_prompt, sampling_params)
+    ref_output = responses[0].outputs[0].text
 
-        # No cascade attention.
+    # (Probably) Use cascade attention.
-        single_prompt = [example_system_message + prompt]
+    prompts = [example_system_message + prompt] * 64
-        responses = llm.generate(single_prompt, sampling_params)
+    responses = llm.generate(prompts, sampling_params)
-        ref_output = responses[0].outputs[0].text
+    for response in responses:
-
+        assert response.outputs[0].text == ref_output
-        # (Probably) Use cascade attention.
-        prompts = [example_system_message + prompt] * 64
-        responses = llm.generate(prompts, sampling_params)
-        for response in responses:
-            assert response.outputs[0].text == ref_output

tests/v1/e2e/test_spec_decode.py

@@ -438,25 +438,26 @@ def test_eagle_correctness(
     should be the same when using eagle speculative decoding.
     model_setup: (method, model_name, eagle_model_name, tp_size)
     """
+    # Determine attention config
+    # Scout requires default backend selection because vision encoder has
+    # head_dim 88 being incompatible with FLASH_ATTN and needs to fall back
+    # to Flex Attn
+    if "Llama-4-Scout" in model_setup[1] and attn_backend == "FLASH_ATTN":
+        if current_platform.is_rocm():
+            # TODO: Enable Flex Attn for spec_decode on ROCm
+            pytest.skip("Flex Attn for spec_decode not supported on ROCm currently")
+        attention_config = None  # Let it fall back to default
+    else:
+        attention_config = {"backend": attn_backend}
+
+    if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
+        pytest.skip(
+            "TRITON_ATTN does not support "
+            "multi-token eagle spec decode on current platform"
+        )
+
     with monkeypatch.context() as m:
-        if "Llama-4-Scout" in model_setup[1] and attn_backend == "FLASH_ATTN":
+        m.setenv("VLLM_MLA_DISABLE", "1")
-            # Scout requires default backend selection
-            # because vision encoder has head_dim 88 being incompatible
-            #  with FLASH_ATTN and needs to fall back to Flex Attn
-
-            # pass if not ROCm
-            if current_platform.is_rocm():
-                # TODO: Enable Flex Attn for spec_decode on ROCm
-                pytest.skip("Flex Attn for spec_decode not supported on ROCm currently")
-        else:
-            m.setenv("VLLM_MLA_DISABLE", "1")
-            m.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
-
-        if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
-            pytest.skip(
-                "TRITON_ATTN does not support "
-                "multi-token eagle spec decode on current platform"
-            )
 
         if attn_backend == "ROCM_AITER_FA" and current_platform.is_rocm():
             if "deepseek" in model_setup[1].lower():
@@ -471,7 +472,10 @@ def test_eagle_correctness(
         max_num_batched_tokens = 128 if enable_chunked_prefill else max_model_len
 
         ref_llm = LLM(
-            model=model_name, max_model_len=max_model_len, tensor_parallel_size=tp_size
+            model=model_name,
+            max_model_len=max_model_len,
+            tensor_parallel_size=tp_size,
+            attention_config=attention_config,
         )
         ref_outputs = ref_llm.chat(test_prompts, sampling_config)
         del ref_llm
@@ -492,6 +496,7 @@ def test_eagle_correctness(
             max_num_batched_tokens=max_num_batched_tokens,
             enable_chunked_prefill=enable_chunked_prefill,
             model_impl=model_impl,
+            attention_config=attention_config,
         )
         spec_outputs = spec_llm.chat(test_prompts, sampling_config)
         matches = 0

tests/v1/kv_connector/nixl_integration/run_accuracy_test.sh

@@ -3,21 +3,29 @@ set -xe
 
 # Parse command line arguments
 KV_BUFFER_DEVICE="cuda"  # Default to cuda
+ATTENTION_BACKEND=""  # Default to empty (use vllm default)
 while [[ $# -gt 0 ]]; do
   case $1 in
     --kv_buffer_device)
       KV_BUFFER_DEVICE="$2"
       shift 2
       ;;
+    --attention-backend)
+      ATTENTION_BACKEND="$2"
+      shift 2
+      ;;
     *)
       echo "Unknown option $1"
-      echo "Usage: $0 [--kv_buffer_device <cuda|cpu>]"
+      echo "Usage: $0 [--kv_buffer_device <cuda|cpu>] [--attention-backend <backend>]"
       exit 1
       ;;
   esac
 done
 
 echo "Running accuracy tests with kv_buffer_device=$KV_BUFFER_DEVICE"
+if [[ -n "$ATTENTION_BACKEND" ]]; then
+  echo "Using attention backend: $ATTENTION_BACKEND"
+fi
 
 DECODER_KV_LAYOUT=${DECODER_KV_LAYOUT:-"HND"} # Default to HND, optional NHD
 if [[ "$DECODER_KV_LAYOUT" == "NHD" ]]; then
@@ -148,6 +156,11 @@ run_tests_for_model() {
     --tensor-parallel-size $PREFILLER_TP_SIZE \
     --kv-transfer-config '$KV_CONFIG'"
 
+    # Add attention backend config if specified
+    if [[ -n "$ATTENTION_BACKEND" ]]; then
+      BASE_CMD="${BASE_CMD} --attention-backend=$ATTENTION_BACKEND"
+    fi
+
     if [ -n "$model_args" ]; then
     FULL_CMD="$BASE_CMD $model_args"
     else
@@ -188,7 +201,12 @@ run_tests_for_model() {
     --block-size ${DECODE_BLOCK_SIZE} \
     --gpu-memory-utilization $GPU_MEMORY_UTILIZATION \
     --kv-transfer-config '$KV_CONFIG'"
-  
+
+    # Add attention backend config if specified
+    if [[ -n "$ATTENTION_BACKEND" ]]; then
+      BASE_CMD="${BASE_CMD} --attention-backend=$ATTENTION_BACKEND"
+    fi
+
   # DP-EP attention mode
   if [[ -z "$DP_EP" ]]; then
     BASE_CMD="${BASE_CMD} --tensor-parallel-size $DECODER_TP_SIZE"

tests/v1/kv_connector/nixl_integration/tp_config_sweep_accuracy_test.sh

@@ -15,14 +15,14 @@ configs=(
 
 run_tests() {
   local label=$1
-  local extra_env=$2
+  local extra_args=$2
 
   echo "=== Running tests (${label}) ==="
   for cfg in "${configs[@]}"; do
-    echo "-> Running with ${cfg} ${extra_env:+and ${extra_env}}"
+    echo "-> Running with ${cfg} ${extra_args:+and ${extra_args}}"
     # Use 'env' to safely set variables without eval
-    if ! env ${extra_env} ${cfg} bash "${SCRIPT}"; then
+    if ! env ${cfg} bash "${SCRIPT}" ${extra_args}; then
-      echo "❌ Test failed for config: ${cfg} ${extra_env:+(${extra_env})}"
+      echo "❌ Test failed for config: ${cfg} ${extra_args:+(${extra_args})}"
       exit 1
     fi
   done
@@ -34,8 +34,8 @@ run_tests "default backend" ""
 
 # Check if FLASHINFER is set (non-empty)
 if [[ -n "${FLASHINFER:-}" ]]; then
-  echo "FLASHINFER is set, rerunning with VLLM_ATTENTION_BACKEND=FLASHINFER"
+  echo "FLASHINFER is set, rerunning with --attention-backend FLASHINFER"
-  run_tests "FLASHINFER backend" "VLLM_ATTENTION_BACKEND=FLASHINFER"
+  run_tests "FLASHINFER backend" "--attention-backend FLASHINFER"
 else
   echo "FLASHINFER not set, skipping FLASHINFER runs."
 fi

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -1132,7 +1132,7 @@ def _run_abort_timeout_test(llm: LLM, timeout: int):
         "TRITON_ATTN",
     ],
 )
-def test_register_kv_caches(dist_init, attn_backend, monkeypatch):
+def test_register_kv_caches(dist_init, attn_backend):
     """
     Test that register_kv_caches() properly calls nixl_wrapper methods with
     correct data.
@@ -1144,9 +1144,7 @@ def test_register_kv_caches(dist_init, attn_backend, monkeypatch):
        block layout info
     """
 
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
+    vllm_config = create_vllm_config(attention_backend=attn_backend)
-
-    vllm_config = create_vllm_config()
 
     # Import the appropriate backend based on the parameter
     if attn_backend == "FLASH_ATTN":

tests/v1/kv_connector/unit/utils.py

@@ -11,6 +11,7 @@ import torch
 
 from vllm import SamplingParams
 from vllm.config import (
+    AttentionConfig,
     CacheConfig,
     DeviceConfig,
     KVTransferConfig,
@@ -94,6 +95,7 @@ def create_vllm_config(
     dtype: str = "float16",
     cache_dtype: str = "auto",
     hf_overrides: dict[str, Any] | None = None,
+    attention_backend: str | None = None,
 ) -> VllmConfig:
     """Initialize VllmConfig For Testing."""
     model_config = ModelConfig(
@@ -124,12 +126,14 @@ def create_vllm_config(
         enable_permute_local_kv=enable_permute_local_kv,
         kv_connector_extra_config=kv_connector_extra_config or {},
     )
+    attention_config = AttentionConfig(backend=attention_backend)
     return VllmConfig(
         scheduler_config=scheduler_config,
         model_config=model_config,
         cache_config=cache_config,
         kv_transfer_config=kv_transfer_config,
         device_config=DeviceConfig("cpu"),
+        attention_config=attention_config,
     )
 
 

tests/v1/kv_offload/test_cpu_offloading.py

@@ -13,7 +13,6 @@ from vllm import LLM, SamplingParams, TokensPrompt
 from vllm.config import KVEventsConfig, KVTransferConfig
 from vllm.distributed.kv_events import BlockStored, KVEventBatch
 from vllm.platforms import current_platform
-from vllm.utils.system_utils import set_env_var
 
 CPU_BLOCK_SIZES = [48]
 ATTN_BACKENDS = ["FLASH_ATTN"]
@@ -180,13 +179,13 @@ def test_cpu_offloading(cpu_block_size: int, attn_backend: str) -> None:
         topic="test",
     )
 
-    with set_env_var("VLLM_ATTENTION_BACKEND", attn_backend):
+    llm = LLM(
-        llm = LLM(
+        model="meta-llama/Llama-3.2-1B-Instruct",
-            model="meta-llama/Llama-3.2-1B-Instruct",
+        gpu_memory_utilization=0.5,
-            gpu_memory_utilization=0.5,
+        kv_events_config=kv_events_config,
-            kv_events_config=kv_events_config,
+        kv_transfer_config=kv_transfer_config,
-            kv_transfer_config=kv_transfer_config,
+        attention_config={"backend": attn_backend},
-        )
+    )
 
     events_endpoint = events_endpoint.replace("*", "127.0.0.1")
     subscriber = MockSubscriber(events_endpoint, topic=kv_events_config.topic)

tests/v1/spec_decode/test_eagle.py

@@ -15,6 +15,7 @@ from tests.v1.attention.utils import (
 )
 from vllm.attention.backends.registry import AttentionBackendEnum
 from vllm.config import (
+    AttentionConfig,
     CacheConfig,
     DeviceConfig,
     ModelConfig,
@@ -38,6 +39,7 @@ eagle3_dir = "yuhuili/EAGLE3-LLaMA3.1-Instruct-8B"
 def _create_proposer(
     method: str,
     num_speculative_tokens: int,
+    attention_backend: str | None = None,
     speculative_token_tree: list[tuple[int, ...]] | None = None,
 ) -> EagleProposer:
     model_config = ModelConfig(model=model_dir, runner="generate", max_model_len=100)
@@ -70,6 +72,7 @@ def _create_proposer(
             max_model_len=model_config.max_model_len,
             is_encoder_decoder=model_config.is_encoder_decoder,
         ),
+        attention_config=AttentionConfig(backend=attention_backend),
     )
 
     return EagleProposer(vllm_config=vllm_config, device=current_platform.device_type)
@@ -331,8 +334,6 @@ def test_load_model(
     use_distinct_lm_head,
     monkeypatch,
 ):
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
-
     if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
         pytest.skip(
             "TRITON_ATTN does not support "
@@ -394,7 +395,9 @@ def test_load_model(
     assert not isinstance(target_model, SupportsMultiModal)
 
     # Create proposer using the helper function
-    proposer = _create_proposer(method, num_speculative_tokens=8)
+    proposer = _create_proposer(
+        method, num_speculative_tokens=8, attention_backend=attn_backend
+    )
 
     # Call the method under test
     proposer.load_model(target_model)
@@ -420,8 +423,6 @@ def test_load_model(
 @pytest.mark.parametrize("attn_backend", get_attn_backend_list_based_on_platform())
 @pytest.mark.parametrize("num_speculative_tokens", [1, 3, 8])
 def test_propose(method, attn_backend, num_speculative_tokens, monkeypatch):
-    monkeypatch.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
-
     if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
         pytest.skip(
             "TRITON_ATTN does not support "
@@ -449,7 +450,9 @@ def test_propose(method, attn_backend, num_speculative_tokens, monkeypatch):
     seq_lens = [seq_len_1, seq_len_2]
 
     # Create proposer first so we can use its actual hidden_size
-    proposer = _create_proposer("eagle", num_speculative_tokens)
+    proposer = _create_proposer(
+        "eagle", num_speculative_tokens, attention_backend=attn_backend
+    )
     # Get the hidden_size from the proposer to ensure consistency
     hidden_size = proposer.hidden_size
 
@@ -622,7 +625,9 @@ def test_propose_tree(spec_token_tree):
 
     # Create proposer first so we can use its actual hidden_size.
     proposer = _create_proposer(
-        "eagle", num_speculative_tokens, speculative_token_tree=spec_token_tree
+        "eagle",
+        num_speculative_tokens,
+        speculative_token_tree=spec_token_tree,
     )
     # Get the hidden_size from the proposer to ensure consistency.
     hidden_size = proposer.hidden_size

tests/v1/spec_decode/test_max_len.py

@@ -38,53 +38,48 @@ def test_ngram_max_len(num_speculative_tokens: int):
 def test_eagle_max_len(
     monkeypatch: pytest.MonkeyPatch, num_speculative_tokens: int, attn_backend: str
 ):
-    with monkeypatch.context() as m:
+    if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
-        m.setenv("VLLM_ATTENTION_BACKEND", attn_backend)
+        pytest.skip(
-
+            "TRITON_ATTN does not support "
-        if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
+            "multi-token eagle spec decode on current platform"
-            pytest.skip(
-                "TRITON_ATTN does not support "
-                "multi-token eagle spec decode on current platform"
-            )
-
-        if attn_backend == "ROCM_AITER_FA" and current_platform.is_rocm():
-            m.setenv("VLLM_ROCM_USE_AITER", "1")
-
-        llm = LLM(
-            model="meta-llama/Meta-Llama-3-8B-Instruct",
-            enforce_eager=True,  # For faster initialization.
-            speculative_config={
-                "method": "eagle",
-                "model": "yuhuili/EAGLE-LLaMA3-Instruct-8B",
-                "num_speculative_tokens": num_speculative_tokens,
-                "max_model_len": 80,
-            },
-            max_model_len=200,
         )
-        sampling_params = SamplingParams(max_tokens=200, ignore_eos=True)
-        outputs = llm.generate(_PROMPTS, sampling_params)
-        for o in outputs:
-            assert o.outputs[0].finish_reason == "length", (
-                "This test is only meaningful if the output "
-                "is truncated due to max length"
-            )
 
-        sampling_params = SamplingParams(
+    if attn_backend == "ROCM_AITER_FA" and current_platform.is_rocm():
-            max_tokens=200,
+        monkeypatch.setenv("VLLM_ROCM_USE_AITER", "1")
-            structured_outputs=StructuredOutputsParams(
+
-                regex="^" + "a b c d e " * 15 + "$"
+    llm = LLM(
-            ),
+        model="meta-llama/Meta-Llama-3-8B-Instruct",
+        enforce_eager=True,  # For faster initialization.
+        speculative_config={
+            "method": "eagle",
+            "model": "yuhuili/EAGLE-LLaMA3-Instruct-8B",
+            "num_speculative_tokens": num_speculative_tokens,
+            "max_model_len": 80,
+        },
+        max_model_len=200,
+        attention_config={"backend": attn_backend},
+    )
+    sampling_params = SamplingParams(max_tokens=200, ignore_eos=True)
+    outputs = llm.generate(_PROMPTS, sampling_params)
+    for o in outputs:
+        assert o.outputs[0].finish_reason == "length", (
+            "This test is only meaningful if the output is truncated due to max length"
         )
-        output = llm.generate(_PROMPTS, sampling_params)
+
-        for o in output:
+    sampling_params = SamplingParams(
-            assert o.prompt_token_ids is not None
+        max_tokens=200,
-            assert (
+        structured_outputs=StructuredOutputsParams(regex="^" + "a b c d e " * 15 + "$"),
-                len(o.prompt_token_ids)
+    )
-                < 80
+    output = llm.generate(_PROMPTS, sampling_params)
-                < len(o.prompt_token_ids) + len(o.outputs[0].token_ids)
+    for o in output:
-                <= 200
+        assert o.prompt_token_ids is not None
-            ), (
+        assert (
-                "This test is only meaningful if the output "
+            len(o.prompt_token_ids)
-                "is longer than the eagle max length"
+            < 80
-            )
+            < len(o.prompt_token_ids) + len(o.outputs[0].token_ids)
-            assert o.outputs[0].text == "a b c d e " * 15
+            <= 200
+        ), (
+            "This test is only meaningful if the output "
+            "is longer than the eagle max length"
+        )
+        assert o.outputs[0].text == "a b c d e " * 15

vllm/v1/attention/backends/rocm_attn.py

@@ -165,7 +165,7 @@ class RocmAttentionBackend(AttentionBackend):
             raise ValueError(
                 f"Head size {head_size} is not supported by {attn_type}. "
                 f"Supported head sizes are: {cls.get_supported_head_sizes()}. "
-                "Set --attention-config.backend=FLEX_ATTENTION to use "
+                "Set --attention-backend=FLEX_ATTENTION to use "
                 "FlexAttention backend which supports all head sizes."
             )