transformers.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

# Copyright 2024 The vLLM team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Wrapper around `transformers` models"""

from collections.abc import Iterable, Mapping
from contextlib import contextmanager
from pathlib import Path
from typing import Literal, Optional, Union

import regex as re
import torch
import transformers
from packaging.version import Version
from torch import nn
from transformers import AutoModel, BatchFeature, PretrainedConfig, PreTrainedModel
from transformers.modeling_utils import ALL_ATTENTION_FUNCTIONS

from vllm.attention import Attention, AttentionType
from vllm.compilation.decorators import support_torch_compile
from vllm.config import (
    CacheConfig,
    DeviceConfig,
    ModelConfig,
    ParallelConfig,
    VllmConfig,
)
from vllm.config.multimodal import BaseDummyOptions
from vllm.config.utils import getattr_iter
from vllm.distributed import get_pp_group, get_tp_group
from vllm.distributed.utils import get_pp_indices
from vllm.logger import init_logger
from vllm.model_executor.layers.layernorm import GemmaRMSNorm, RMSNorm
from vllm.model_executor.layers.linear import (
    ColumnParallelLinear,
    ReplicatedLinear,
    RowParallelLinear,
)
from vllm.model_executor.layers.logits_processor import LogitsProcessor
from vllm.model_executor.layers.quantization import QuantizationConfig
from vllm.model_executor.layers.vocab_parallel_embedding import (
    ParallelLMHead,
    VocabParallelEmbedding,
)
from vllm.multimodal import MULTIMODAL_REGISTRY, MultiModalKwargsItems
from vllm.multimodal.inputs import (
    MultiModalDataDict,
    MultiModalFieldConfig,
    MultiModalInputs,
    MultiModalUUIDDict,
    PlaceholderRange,
)
from vllm.multimodal.parse import ImageProcessorItems, MultiModalDataItems
from vllm.multimodal.processing import BaseMultiModalProcessor, BaseProcessingInfo
from vllm.multimodal.profiling import BaseDummyInputsBuilder
from vllm.sequence import IntermediateTensors

from .interfaces import SupportsLoRA, SupportsMultiModal, SupportsPP, SupportsQuant
from .utils import (
    AutoWeightsLoader,
    PPMissingLayer,
    WeightsMapper,
    make_empty_intermediate_tensors_factory,
    maybe_prefix,
)

logger = init_logger(__name__)


def get_feature_request_tip(
    model: str,
    trust_remote_code: bool,
) -> str:
    hf_url = f"a discussion at https://huggingface.co/{model}/discussions/new"
    gh_url = "an issue at https://github.com/huggingface/transformers/issues/new/choose"
    url = hf_url if trust_remote_code else gh_url
    prefix = f"Please open {url} to request support for this feature. "
    if Path(model).exists():
        prefix = ""
    doc_url = "https://docs.vllm.ai/en/latest/models/supported_models.html#writing-custom-models"
    tip = f"See {doc_url} for instructions on how to add support yourself."
    return f"{prefix}{tip}"


def vllm_flash_attention_forward(
    # Transformers args
    module: torch.nn.Module,
    query: torch.Tensor,
    key: torch.Tensor,
    value: torch.Tensor,
    attention_mask: torch.Tensor,
    # Transformers kwargs
    scaling: Optional[float] = None,
    # vLLM kwargs
    attention_instances: Optional[dict[Attention]] = None,
    **kwargs,
):
    self_attn = attention_instances[module.layer_idx]
    if scaling is not None:
        self_attn.impl.scale = float(scaling)
    hidden = query.shape[-2]
    query, key, value = (x.transpose(1, 2) for x in (query, key, value))
    query, key, value = (x.reshape(hidden, -1) for x in (query, key, value))
    return self_attn.forward(query, key, value), None


ALL_ATTENTION_FUNCTIONS["vllm"] = vllm_flash_attention_forward


def log_replacement(name: str, old_module: nn.Module, new_module: nn.Module):
    logger.debug("%s: %s -> %s", name, old_module, new_module)


def can_enable_torch_compile(vllm_config: VllmConfig) -> bool:
    """
    Callable to be passed to `@support_torch_compile`'s `enable_if` argument.

    Defaults to `True` but is disabled in the following situations:

    - The model uses dynamic rope scaling.
    """
    enable = True
    text_config = vllm_config.model_config.hf_config.get_text_config()
    # Dynamic rope scaling is not compatible with torch.compile
    rope_scaling: dict = getattr(text_config, "rope_scaling", None) or {}
    if rope_scaling.get("rope_type") == "dynamic":
        enable = False
    return enable


Style = Literal["colwise", "colwise_rep", "rowwise", "rowwise_rep", "replicate"]


def replace_linear_class(
    linear: nn.Linear,
    style: Style = "replicate",
    quant_config: Optional[QuantizationConfig] = None,
    *,
    prefix: str = "",
) -> Union[ColumnParallelLinear, RowParallelLinear, ReplicatedLinear]:
    """
    Replace nn.Linear with one of vLLM's tensor parallel linear classes.

    Args:
        linear: `nn.Linear` to be replaced.
        style: Tensor parallel style of the new linear, e.g. "colwise".
        quant_config: Quantization config for the new linear.
    Returns:
        The new linear.
    """

    if not isinstance(style, str):
        raise ValueError(f"Unsupported parallel style type {type(style)}, expected str")

    vllm_linear_cls, vllm_linear_kwargs = {
        "colwise": (ColumnParallelLinear, {}),
        "colwise_rep": (ColumnParallelLinear, {"gather_output": True}),
        "rowwise": (RowParallelLinear, {}),
        "rowwise_rep": (RowParallelLinear, {"input_is_parallel": False}),
        "replicate": (ReplicatedLinear, {}),
    }.get(style, (ReplicatedLinear, {}))

    return vllm_linear_cls(
        input_size=linear.in_features,
        output_size=linear.out_features,
        bias=linear.bias is not None,
        quant_config=quant_config,
        prefix=prefix,
        return_bias=False,
        **vllm_linear_kwargs,
    )


def replace_rms_norm_class(rms_norm: nn.Module, hidden_size: int) -> RMSNorm:
    """Replace a Transformers RMSNorm with vLLM's RMSNorm.

    This method assumes:
    - Weight is stored as `weight`.
    - Epsilon is stored as `eps` or `variance_epsilon`.
    - `with_scale` indicates whether the layer has a weight (Gemma3n only).
    - `var_hidden_size` is only ever used for Intern vision encoder in vLLM
    and Transformers doesn't appear to have the same concept.
    """
    eps = getattr_iter(rms_norm, ("eps", "variance_epsilon"), 1e-6)
    kwargs = {"hidden_size": hidden_size, "eps": eps}
    # Update hidden size if weight is available
    weight_meta = getattr(rms_norm, "weight", None)
    if weight_meta is not None:
        kwargs["hidden_size"] = weight_meta.size(0)
    # Check if weight is all zeros, which indicates GemmaRMSNorm
    # We must create a new instance because rms_norm is on meta
    try:
        with torch.device("cpu"):
            weight_test = getattr(rms_norm.__class__(1), "weight", None)
    except Exception:
        logger.warning(
            "Failed to determine if RMSNorm weight is centered on zero or one. "
            "Defaulting to one."
        )
        weight_test = None
    if weight_test is not None and torch.all(weight_test == 0):
        return GemmaRMSNorm(**kwargs)
    # Otherwise assume it's a regular RMSNorm
    kwargs["has_weight"] = getattr(rms_norm, "with_scale", True)
    if weight_meta is not None:
        kwargs["dtype"] = weight_meta.dtype
    else:
        # No weight, fall back to weightless RMSNorm
        kwargs["has_weight"] = False
    return RMSNorm(**kwargs)


# Copied from `accelerate`
@contextmanager
def init_on_device_without_buffers(device: torch.device):
    """
    A context manager under which models are initialized with all
    parameters on the specified device. However buffers are not
    initialized on specified device.

    Args:
        device (`torch.device`):
            Device to initialize all parameters on.
    """

    old_register_parameter = nn.Module.register_parameter

    def register_empty_parameter(module, name, param):
        old_register_parameter(module, name, param)
        if param is not None:
            param_cls = type(module._parameters[name])
            kwargs = module._parameters[name].__dict__
            kwargs["requires_grad"] = param.requires_grad
            module._parameters[name] = param_cls(
                module._parameters[name].to(device), **kwargs
            )

    tensor_constructors_to_patch = {}

    def patch_tensor_constructor(fn):
        def wrapper(*args, **kwargs):
            kwargs["device"] = device
            return fn(*args, **kwargs)

        return wrapper

    try:
        nn.Module.register_parameter = register_empty_parameter
        for torch_function_name in tensor_constructors_to_patch:
            setattr(
                torch,
                torch_function_name,
                patch_tensor_constructor(getattr(torch, torch_function_name)),
            )
        yield
    finally:
        nn.Module.register_parameter = old_register_parameter
        for (
            torch_function_name,
            old_torch_function,
        ) in tensor_constructors_to_patch.items():
            setattr(torch, torch_function_name, old_torch_function)


class MultiModalProcessingInfo(BaseProcessingInfo):
    def get_supported_mm_limits(self):
        return {"image": None}

    def get_mm_max_tokens_per_item(self, seq_len, mm_counts):
        return {"image": self.get_max_image_tokens()}

    def get_max_image_tokens(self) -> int:
        width, height = self.get_max_image_size()
        processor = self.get_hf_processor()
        multimodal_config = self.ctx.model_config.multimodal_config
        mm_processor_kwargs = multimodal_config.mm_processor_kwargs or {}
        mm_tokens = processor._get_num_multimodal_tokens(
            image_sizes=([height, width],), **mm_processor_kwargs
        )
        image_tokens = mm_tokens["num_image_tokens"][0]
        return image_tokens

    def get_max_image_size(self):
        return 10_000, 10_000  # hardcode for arbitrary very large size


class MultiModalDummyInputsBuilder(BaseDummyInputsBuilder[MultiModalProcessingInfo]):
    def get_dummy_text(self, mm_counts: Mapping[str, int]) -> str:
        num_images = mm_counts.get("image", 0)

        processor = self.info.get_hf_processor()
        if "gemma3" in processor.__class__.__name__.lower():
            image_token = processor.boi_token
        else:
            image_token = getattr(processor, "image_token", "")
        return image_token * num_images

    def get_dummy_mm_data(
        self,
        seq_len: int,
        mm_counts: Mapping[str, int],
        mm_options: Optional[Mapping[str, BaseDummyOptions]] = None,
    ) -> MultiModalDataDict:
        num_images = mm_counts.get("image", 0)

        target_width, target_height = self.info.get_max_image_size()

        image_overrides = mm_options.get("image") if mm_options else None

        return {
            "image": self._get_dummy_images(
                width=target_width,
                height=target_height,
                num_images=num_images,
                overrides=image_overrides,
            ),
        }


class MultiModalProcessor(BaseMultiModalProcessor[MultiModalProcessingInfo]):
    def _get_prompt_updates(
        self,
        mm_items: MultiModalDataItems,
        hf_processor_mm_kwargs: Mapping[str, object],
        out_mm_kwargs: MultiModalKwargsItems,
    ):
        """
        Given the original multi-modal items for this modality
        and HF-processed data, output the updates to perform.

        The information returned by this method is used to update token inputs
        which bypass the HF processor. It is also used to update the output of
        HF processor if the HF process does not apply prompt updates to text
        inputs.

        Moreover, this information is critical to determine the token positions
        in order to construct  :class:`~vllm-multimodal.input.PlaceholderRange`
        for each multi-modal item.
        """
        return None

    def _get_mm_fields_config(
        self,
        hf_inputs: BatchFeature,
        hf_processor_mm_kwargs: Mapping[str, object],
    ) -> Mapping[str, MultiModalFieldConfig]:
        # HF Processors always return a mask but vLLM doesn't need it
        hf_inputs.pop("attention_mask", None)
        num_image_patches = hf_inputs.get("num_image_patches")
        mm_fields = {
            key: MultiModalFieldConfig.flat_from_sizes("image", num_image_patches)
            for key in hf_inputs
        }
        mm_fields["image_embeds"] = MultiModalFieldConfig.flat_from_sizes(
            "image", num_image_patches
        )

        # Keep these as batched, as they always have batch size as first dim
        mm_fields["image_grid_thw"] = MultiModalFieldConfig.batched("image")
        mm_fields["video_grid_thw"] = MultiModalFieldConfig.batched("image")
        mm_fields["num_image_patches"] = MultiModalFieldConfig.batched("image")
        return mm_fields

    def _get_hf_mm_data(
        self,
        mm_items: MultiModalDataItems,
    ) -> tuple[Mapping[str, object], Mapping[str, object]]:
        """
        In contrast to the base class, this method always adds
        `return_mm_token_type_ids` to the processor data
        """
        processor_data, passthrough_data = super()._get_hf_mm_data(mm_items)
        processor_data["return_mm_token_type_ids"] = True
        return processor_data, passthrough_data

    def apply(
        self,
        prompt: Union[str, list[int]],
        mm_data: MultiModalDataDict,
        hf_processor_mm_kwargs: Mapping[str, object],
        tokenization_kwargs: Optional[Mapping[str, object]] = None,
        mm_uuids: Optional[MultiModalUUIDDict] = None,
    ) -> MultiModalInputs:
        """
        Process multi-modal inputs to be used in vLLM.

        Apply HF Processor on prompt text and multi-modal data together,
        outputting token IDs and processed tensors.
        """
        if tokenization_kwargs is None:
            tokenization_kwargs = {}

        mm_items = self._to_mm_items(mm_data)
        hf_processor = self.info.get_hf_processor(**hf_processor_mm_kwargs)
        if not isinstance(prompt, str):
            # the prompt is the tokenized ids which is not supported
            # by the hf_processor, which is why we would need to decode the ids
            # into string
            prompt = hf_processor.decode(prompt)

        # Bypass cached processor and always apply to the full set of mm inputs
        # NOTE: we can't just set caching=False because base class method
        # transforms outputs to `MultiModalKwargs` which is not going to
        # work for Transformers. We have a lot of logic tied to
        # `mm_tokens_per_modality` below
        prompt_ids, processed_data, _ = self._apply_hf_processor_text_mm(
            prompt_text=prompt,
            mm_items=mm_items,
            hf_processor_mm_kwargs=hf_processor_mm_kwargs,
            tokenization_kwargs=tokenization_kwargs,
        )

        # For gemma3 we check `token_type_ids` as the key
        token_type_key = (
            "mm_token_type_ids"
            if "mm_token_type_ids" in processed_data
            else "token_type_ids"
        )
        mm_token_type_ids = processed_data.pop(token_type_key)

        # We can infer vLLM style placeholder from token type ids, if we split
        # it for each input `mm_data`.
        mm_positions = torch.where(mm_token_type_ids == 1)[1]
        images = mm_items.get_items("image", ImageProcessorItems)
        multimodal_config = self.info.ctx.model_config.multimodal_config
        mm_processor_kwargs = multimodal_config.mm_processor_kwargs or {}
        image_sizes = []
        for item_idx in range(len(images)):
            image_size = images.get_image_size(item_idx)
            image_sizes.append((image_size.height, image_size.width))

        mm_tokens_per_modality = hf_processor._get_num_multimodal_tokens(
            image_sizes=image_sizes, **mm_processor_kwargs
        )

        mm_placeholders = {}
        split_sizes = mm_tokens_per_modality["num_image_tokens"]
        if split_sizes:
            chunked_mm_positions = torch.split(mm_positions, split_sizes)
            mm_tokens = torch.tensor(prompt_ids)[mm_token_type_ids[0].bool()]
            chunked_mm_tokens = torch.split(mm_tokens, split_sizes)
            ranges = [
                PlaceholderRange(
                    offset=positions[0].item(),
                    length=positions.shape[0],
                    is_embed=(mm_tokens == hf_processor.image_token_id).bool(),
                )
                for positions, mm_tokens in zip(chunked_mm_positions, chunked_mm_tokens)
            ]
            mm_placeholders = {"image": ranges}

        processed_data["num_image_patches"] = torch.tensor(
            mm_tokens_per_modality["num_image_patches"]
        )
        mm_kwargs = MultiModalKwargsItems.from_hf_inputs(
            processed_data,
            self._get_mm_fields_config(processed_data, hf_processor_mm_kwargs),
        )

        # Use overrides if provided; fallback to data-dependent hashing.
        mm_hashes = self._hash_mm_items(
            mm_items, hf_processor_mm_kwargs, tokenization_kwargs, mm_uuids=mm_uuids
        )

        return MultiModalInputs(
            type="multimodal",
            prompt_token_ids=prompt_ids,
            mm_kwargs=mm_kwargs,
            mm_hashes=mm_hashes,
            mm_placeholders=mm_placeholders,
        )


class TransformersBase(nn.Module, SupportsQuant, SupportsLoRA, SupportsPP):
    embedding_padding_modules = ["lm_head"]
    embedding_modules = ["embed_tokens"]  # TODO transformers will have a util to get it

    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__()
        logger.info("Using Transformers backend.")

        self.config: PretrainedConfig = vllm_config.model_config.hf_config
        self.text_config: PretrainedConfig = self.config.get_text_config()
        self.cache_config: CacheConfig = vllm_config.cache_config
        self.device_config: DeviceConfig = vllm_config.device_config
        self.model_config: ModelConfig = vllm_config.model_config
        self.parallel_config: ParallelConfig = vllm_config.parallel_config
        self.quant_config: Optional[QuantizationConfig] = vllm_config.quant_config

        self.pp_group = get_pp_group()
        self.tp_group = get_tp_group()

        # Weights to skip in `self.load_weights`
        self.skip_prefixes: list[str] = []
        """Skip loading weights whose qualname starts with these prefixes."""
        self.skip_substrs: list[str] = []
        """Skip loading weights whose qualname contains these substrings."""
        self.ignore_unexpected_prefixes: list[str] = []
        """Ignore unexpected weights whose qualname starts with these prefixes.
        """
        self.ignore_unexpected_suffixes: list[str] = []
        """Ignore unexpected weights whose qualname ends with these suffixes."""

        if self.quant_config:
            quant_method_name = self.quant_config.get_name()
            # Check for unsupported quantization methods.
            if quant_method_name == "mxfp4":
                raise NotImplementedError(
                    "Transformers backend does not support MXFP4 quantization yet."
                )
            # Skip loading extra bias for GPTQ models.
            if "gptq" in quant_method_name:
                self.ignore_unexpected_suffixes.append(".bias")

        # Set correct attn and init on "meta" to delay allocating GPU tensors
        self.text_config._attn_implementation = "vllm"
        with init_on_device_without_buffers("meta"):
            self.model: PreTrainedModel = AutoModel.from_config(
                self.config,
                torch_dtype=self.model_config.dtype,
                trust_remote_code=self.model_config.trust_remote_code,
            )

        # Remove layers not on this pipeline parallel rank
        self.pipeline_parallel()
        # Substitute remaining layers with vLLM's layers as needed
        self.recursive_replace()
        # Create attention instances for KV cache allocation
        self.attention_instances = self.create_attention_instances()

        # Input embeddings
        input_embeddings = self.model.get_input_embeddings()
        if not isinstance(input_embeddings, PPMissingLayer):
            # Some models use embedding scales
            self.embed_scale = getattr(input_embeddings, "embed_scale", None)
            names = ("embedding_size", "hidden_size")
            embedding_dim = getattr_iter(self.text_config, names, None)
            assert embedding_dim is not None
            self.model.set_input_embeddings(
                VocabParallelEmbedding(
                    self.text_config.vocab_size,
                    embedding_dim=embedding_dim,
                    org_num_embeddings=self.text_config.vocab_size,
                    quant_config=self.quant_config,
                )
            )

        # Initialize any parameters that have not had their modules replaced
        self.init_parameters(self.model)

        # Pipeline parallel intermediate tensors
        self.make_empty_intermediate_tensors = make_empty_intermediate_tensors_factory(
            ["hidden_states"], self.text_config.hidden_size
        )

    def pipeline_parallel(self):
        """
        Apply the model's pipeline parallelization plan.
        """
        if self.pp_group.world_size <= 1:
            return

        if not self.model.supports_pp_plan:
            tip = get_feature_request_tip(
                self.model_config.model, self.model_config.trust_remote_code
            )
            raise ValueError(
                f"{type(self.model)} does not support pipeline parallel. {tip}"
            )

        module_lists = []
        module_list_idx = None
        pp_plan = list(self.model._pp_plan.keys())
        for i, name in enumerate(pp_plan):
            if isinstance(getattr(self.model, name), nn.ModuleList):
                module_lists.append(name)
                module_list_idx = i

        if len(module_lists) > 1:
            raise ValueError(
                "Pipeline parallel of models with multiple `ModuleList`s "
                "in the base model are not supported yet!"
            )
        if module_list_idx is None:
            raise ValueError(f"Could not find `ModuleList` in {type(self.model)}")

        # Layers before module list
        for name in pp_plan[:module_list_idx]:
            if self.pp_group.is_first_rank or (
                self.text_config.tie_word_embeddings and self.pp_group.is_last_rank
            ):
                continue
            setattr(self.model, name, PPMissingLayer())

        # Module list
        start_layer, end_layer = get_pp_indices(
            self.text_config.num_hidden_layers,
            self.pp_group.rank_in_group,
            self.pp_group.world_size,
        )
        layers_name = pp_plan[module_list_idx]
        layers = getattr(self.model, layers_name)
        for i in range(len(layers)):
            if start_layer <= i and i < end_layer:
                continue
            layers[i] = PPMissingLayer()

        # Layers after module list
        for name in pp_plan[module_list_idx + 1 :]:
            # Modules that should be on last rank
            if not self.pp_group.is_last_rank:
                setattr(self.model, name, PPMissingLayer())

    def recursive_replace(self):
        """Recursively replace modules in the model as needed.

        Currently, this replaces:

        - `nn.Linear` with vLLM's tensor parallel linear classes
        - `*RMSNorm` with vLLM's `RMSNorm`
        """
        tp_plan = self.model.tp_plan

        if not tp_plan and self.tp_group.world_size > 1:
            tip = get_feature_request_tip(
                self.model_config.model, self.model_config.trust_remote_code
            )
            raise ValueError(
                f"{type(self.model)} does not support tensor parallel. {tip}"
            )

        # Prefix the patterns because we always start from `self.model`
        tp_plan = {maybe_prefix("model", k): v for k, v in tp_plan.items()}

        def _recursive_replace(module: nn.Module, prefix: str):
            for child_name, child_module in module.named_children():
                new_module = child_module
                qual_name = maybe_prefix(prefix, child_name)
                if isinstance(child_module, nn.Linear):
                    generator = (p for p in tp_plan if re.match(p, qual_name))
                    pattern = next(generator, None)
                    # Some weight loaders expect all linear layers to inherit
                    # LinearBase, so we set a default style which causes any
                    # unspecified layers to be replaced with ReplicatedLinear
                    style = tp_plan.get(pattern, "replicate")
                    new_module = replace_linear_class(
                        child_module, style, self.quant_config, prefix=qual_name
                    )
                elif child_module.__class__.__name__.endswith("RMSNorm"):
                    new_module = replace_rms_norm_class(
                        child_module, self.text_config.hidden_size
                    )
                else:
                    _recursive_replace(child_module, prefix=qual_name)

                if new_module is not child_module:
                    setattr(module, child_name, new_module)
                    log_replacement(qual_name, child_module, new_module)

        _recursive_replace(self.model, prefix="model")

    def create_attention_instances(
        self, attn_type: AttentionType = AttentionType.DECODER
    ) -> dict[int, Attention]:
        """
        Create `Attention` instances to inform KV cache allocation.
        """
        num_heads = self.model_config.get_num_attention_heads(self.parallel_config)
        head_size = self.model_config.get_head_size()
        num_kv_heads = self.model_config.get_num_kv_heads(self.parallel_config)
        logits_soft_cap = getattr(self.text_config, "attn_logit_softcapping", None)
        start, end = get_pp_indices(
            self.text_config.num_hidden_layers,
            self.pp_group.rank_in_group,
            self.pp_group.world_size,
        )

        attention_instances = {}
        for i in range(start, end):
            # Handle interleaved sliding window attention
            per_layer_sliding_window = None
            if (
                hasattr(self.config, "layer_types")
                and self.config.layer_types[i] == "sliding_attention"
            ):
                per_layer_sliding_window = self.config.sliding_window

            attention_instances[i] = Attention(
                num_heads=num_heads,
                head_size=head_size,
                # NOTE: We use Llama scale as default, if it's set by
                # Transformers, it's updated in vllm_flash_attention_forward
                scale=head_size**-0.5,
                num_kv_heads=num_kv_heads,
                cache_config=self.cache_config,
                quant_config=self.quant_config,
                logits_soft_cap=logits_soft_cap,
                per_layer_sliding_window=per_layer_sliding_window,
                prefix=f"{i}.attn",
                attn_type=attn_type,
            )
        return attention_instances

    def init_parameters(self, module: nn.Module, dtype: Optional[torch.dtype] = None):
        """
        If a `parameter` is on the `meta` device, then its parent
        `module` is the original module created by:

        ```python
        with torch.device("meta"):
            self.model: PreTrainedModel = AutoModel.from_config(...)
        ```
        """

        def _init_parameters(module: nn.Module, dtype: Optional[torch.dtype]):
            for name, param in module.named_parameters(recurse=False):
                if param.device == torch.device("meta"):
                    new_param = nn.Parameter(
                        torch.empty_like(
                            param.data,
                            dtype=dtype or self.model_config.dtype,
                            device=self.device_config.device,
                        )
                    )
                    setattr(module, name, new_param)
            for child in module.children():
                _init_parameters(child, dtype)

        _init_parameters(module, dtype)

    def forward(
        self,
        input_ids: Optional[torch.Tensor],
        positions: torch.Tensor,
        intermediate_tensors: Optional[IntermediateTensors] = None,
        inputs_embeds: Optional[torch.Tensor] = None,
        **kwargs,
    ) -> Union[torch.Tensor, IntermediateTensors]:
        if not self.pp_group.is_first_rank:
            assert intermediate_tensors is not None
            input_ids = None
            inputs_embeds = intermediate_tensors["hidden_states"]

        if input_ids is not None:
            input_ids = input_ids[None, ...]
        if inputs_embeds is not None:
            inputs_embeds = inputs_embeds[None, ...]

        if self.model_config.uses_mrope:
            position_ids = positions[:, None]
        else:
            position_ids = positions[None, ...]

        hidden_states = self.model(
            input_ids=input_ids,
            inputs_embeds=inputs_embeds,
            use_cache=False,
            position_ids=position_ids,
            attention_instances=self.attention_instances,
            return_dict=False,
            **kwargs,
        )[0][0, ...]  # we remove batch dimension for now

        if not self.pp_group.is_last_rank:
            return IntermediateTensors({"hidden_states": hidden_states})

        return hidden_states

    def load_weights(
        self,
        weights: Iterable[tuple[str, torch.Tensor]],
    ) -> set[str]:
        loader = AutoWeightsLoader(
            self,
            skip_prefixes=self.skip_prefixes,
            skip_substrs=self.skip_substrs,
            ignore_unexpected_prefixes=self.ignore_unexpected_prefixes,
            ignore_unexpected_suffixes=self.ignore_unexpected_suffixes,
        )
        return loader.load_weights(weights, mapper=self.hf_to_vllm_mapper)

    def check_version(self, min_version: str, feature: str):
        installed = Version(transformers.__version__)
        required = Version(min_version)
        if installed < required:
            raise ImportError(
                f"Transformers backend requires transformers>={required} "
                f"for {feature}, but got {installed}"
            )


@support_torch_compile(enable_if=can_enable_torch_compile)
class TransformersForCausalLM(TransformersBase):
    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__(vllm_config=vllm_config, prefix=prefix)

        # Tell `TransformersBase.load_weights` to skip
        # `lm_head` if the model has tied word embeddings
        if self.text_config.tie_word_embeddings:
            self.skip_prefixes.append("lm_head.")

        if self.pp_group.is_last_rank:
            self.unpadded_vocab_size = self.text_config.vocab_size
            self.lm_head = ParallelLMHead(
                self.text_config.vocab_size,
                self.text_config.hidden_size,
                quant_config=self.quant_config,
                prefix=maybe_prefix(prefix, "lm_head"),
            )
            if self.text_config.tie_word_embeddings:
                self.lm_head = self.lm_head.tie_weights(
                    self.model.get_input_embeddings()
                )

            logit_scale = getattr(self.text_config, "logit_scale", 1.0)
            self.logits_processor = LogitsProcessor(
                self.unpadded_vocab_size, self.text_config.vocab_size, logit_scale
            )
        else:
            self.lm_head = PPMissingLayer()

    def get_input_embeddings(self, input_ids: torch.Tensor) -> torch.Tensor:
        inputs_embeds = self.model.get_input_embeddings()(input_ids)
        if self.embed_scale is not None:
            inputs_embeds *= self.embed_scale
        return inputs_embeds

    def compute_logits(
        self,
        hidden_states: torch.Tensor,
    ) -> Optional[torch.Tensor]:
        logits = self.logits_processor(self.lm_head, hidden_states)
        return logits


@MULTIMODAL_REGISTRY.register_processor(
    MultiModalProcessor,
    info=MultiModalProcessingInfo,
    dummy_inputs=MultiModalDummyInputsBuilder,
)
@support_torch_compile(
    # set `positions` to last dim to support Qwen-mrope
    dynamic_arg_dims={
        "input_ids": 0,
        "positions": -1,
        "intermediate_tensors": 0,
        "inputs_embeds": 0,
    },
    enable_if=can_enable_torch_compile,
)
class TransformersForMultimodalLM(TransformersForCausalLM, SupportsMultiModal):
    supports_multimodal_raw_input_only = True
    merge_by_field_config = True
    # Backwards compatibility for prev released models. State dicts back then
    # had different formats and cannot be loaded with `AutoModel` mapping as is
    hf_to_vllm_mapper = WeightsMapper(
        orig_to_new_prefix={
            "language_model.model": "model.language_model",
            "text_model.model": "model.text_model",
            "vision_tower": "model.vision_tower",
            "vqmodel": "model.vqmodel",
            "visual": "model.visual",
            "vision_model": "model.vision_model",
            "vision_embed_tokens": "model.vision_embed_tokens",
            "image_newline": "model.image_newline",
            "multi_modal_projector": "model.multi_modal_projector",
            "text_model.lm_head": "lm_head",
            "language_model.lm_head": "lm_head",
            # Qwen models used "model" as the name for the language model.
            # Therefore, we must map each of submodule explicitly to avoid
            # conflicts with newer models that use "model.language_model".
            "model.embed_tokens": "model.language_model.embed_tokens",
            "model.layers": "model.language_model.layers",
            "model.norm": "model.language_model.norm",
        }
    )

    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__(vllm_config=vllm_config, prefix=prefix)

        self.dtype = vllm_config.model_config.dtype

    def forward(
        self,
        input_ids: Optional[torch.Tensor],
        positions: torch.Tensor,
        intermediate_tensors: Optional[IntermediateTensors] = None,
        inputs_embeds: Optional[torch.Tensor] = None,
        **kwargs: object,
    ) -> Union[torch.Tensor, IntermediateTensors]:
        # Gemma3 and PaliGemma needs `token_type_ids` to work correctly
        # Other models will not have `token_type_ids` in kwargs
        kwargs = {k: v for k, v in kwargs.items() if k == "token_type_ids"}
        model_output = super().forward(
            input_ids, positions, intermediate_tensors, inputs_embeds, **kwargs
        )
        return model_output

    def get_language_model(self) -> torch.nn.Module:
        """`TransformersForMultimodalLM` does not contain a vLLM language model class.
        Therefore, in order to return a language model vLLM class, we use a wrapper to
        give `self` the same interface as `TransformersForCausalLM`."""

        class LanguageModelWrapper(TransformersForCausalLM):
            def __init__(self, multimodal_model):
                # Don't call super().__init__() to avoid re-initialization
                self.__dict__.update(multimodal_model.__dict__)

            model = getattr_iter(self.model, ("language_model", "text_model"), None)

        return LanguageModelWrapper(self)

    def get_multimodal_embeddings(self, **kwargs):
        pixel_values: Optional[torch.Tensor] = kwargs.pop("pixel_values", None)
        image_embeds: Optional[torch.Tensor] = kwargs.pop("image_embeds", None)
        # Model might use `image_patches` instead of `pixel_values`
        if pixel_values is None:
            pixel_values = kwargs.pop("image_patches", None)

        if image_embeds is not None:
            return image_embeds

        if pixel_values is None:
            return None

        num_image_patches = kwargs.pop("num_image_patches")
        kwargs.pop("token_type_ids", None)  # used only in `forward`
        if pixel_values is not None:
            vision_embeddings = self.model.get_image_features(pixel_values, **kwargs)

            if isinstance(vision_embeddings, torch.Tensor):
                if vision_embeddings.ndim == 2:
                    vision_embeddings = vision_embeddings.unsqueeze(0)

                # Embeddings have to be 2D tensors of length `num_images`
                # but transformers returns concat tensors if each patch
                # is of different size. We split it back to make vLLM happy
                vision_embeddings = torch.split(
                    vision_embeddings, num_image_patches.flatten().tolist()
                )
                vision_embeddings = [
                    embed.flatten(start_dim=0, end_dim=-2)
                    for embed in vision_embeddings
                ]

            return vision_embeddings

    get_input_embeddings = SupportsMultiModal.get_input_embeddings