[Gemma Embedding] Fix SWA (#40700)

* fix gemma embedding flash attention

* fix sdpa

* fix atttempt number 2

* alternative gemma fix

* fix modular

Author: vasqu

src/transformers/models/gemma3/configuration_gemma3.py

@@ -226,6 +226,8 @@ def __init__(
         self.attn_logit_softcapping = attn_logit_softcapping
         self.layer_types = layer_types
         self.use_bidirectional_attention = use_bidirectional_attention
+        if use_bidirectional_attention:
+            self.sliding_window = (self.sliding_window // 2) + 1  # due to fa we set exclusive bounds
 
         self.rope_local_base_freq = rope_local_base_freq
         self.rope_scaling = rope_scaling

src/transformers/models/gemma3/modeling_gemma3.py

@@ -279,7 +279,7 @@ def __init__(self, config: Gemma3TextConfig, layer_idx: int):
         self.num_key_value_groups = config.num_attention_heads // config.num_key_value_heads
         self.scaling = config.query_pre_attn_scalar**-0.5
         self.attention_dropout = self.config.attention_dropout
-        self.is_causal = True
+        self.is_causal = not self.config.use_bidirectional_attention
 
         self.q_proj = nn.Linear(
             config.hidden_size, config.num_attention_heads * self.head_dim, bias=config.attention_bias
@@ -450,8 +450,8 @@ def _bidirectional_window_overlay(sliding_window: int) -> Callable[[int, int, in
 
     def inner_mask(batch_idx: int, head_idx: int, q_idx: int, kv_idx: int) -> bool:
         """A token can attend to any other token if their absolute distance is within
-        half the sliding window size (distance <= sliding_window // 2)."""
-        return abs(q_idx - kv_idx) <= sliding_window // 2
+        the (exclusive) sliding window size (distance < sliding_window)."""
+        return abs(q_idx - kv_idx) < sliding_window
 
     return inner_mask
 

src/transformers/models/gemma3/modular_gemma3.py

@@ -237,6 +237,8 @@ def __init__(
         self.attn_logit_softcapping = attn_logit_softcapping
         self.layer_types = layer_types
         self.use_bidirectional_attention = use_bidirectional_attention
+        if use_bidirectional_attention:
+            self.sliding_window = (self.sliding_window // 2) + 1  # due to fa we set exclusive bounds
 
         self.rope_local_base_freq = rope_local_base_freq
         self.rope_scaling = rope_scaling
@@ -402,6 +404,7 @@ def __init__(self, config: Gemma3TextConfig, layer_idx: int):
 
         super().__init__(config, layer_idx)
         self.sliding_window = config.sliding_window if self.is_sliding else None
+        self.is_causal = not self.config.use_bidirectional_attention
 
         self.q_norm = Gemma3RMSNorm(dim=config.head_dim, eps=config.rms_norm_eps)
         self.k_norm = Gemma3RMSNorm(dim=config.head_dim, eps=config.rms_norm_eps)
@@ -546,8 +549,8 @@ def _bidirectional_window_overlay(sliding_window: int) -> Callable[[int, int, in
 
     def inner_mask(batch_idx: int, head_idx: int, q_idx: int, kv_idx: int) -> bool:
         """A token can attend to any other token if their absolute distance is within
-        half the sliding window size (distance <= sliding_window // 2)."""
-        return abs(q_idx - kv_idx) <= sliding_window // 2
+        the (exclusive) sliding window size (distance < sliding_window)."""
+        return abs(q_idx - kv_idx) < sliding_window
 
     return inner_mask
 

src/transformers/models/gemma3n/modular_gemma3n.py

@@ -1744,6 +1744,7 @@ def apply_rotary_pos_emb(
 class Gemma3nTextAttention(Gemma3Attention):
     def __init__(self, config: Gemma3nTextConfig, layer_idx: int):
         super().__init__(config, layer_idx)
+        self.is_causal = True
         del self.attn_logit_softcapping
         del self.scaling
         self.v_norm = Gemma3nRMSNorm(dim=config.head_dim, eps=config.rms_norm_eps, with_scale=False)