fix: Enable KD plugin support for PEFT/LoRA adapters (#3207)

- Fix _loss_function attribute not found on base model with PEFT
- Fix mismatched attribute name (loss_function vs _loss_function)
- Set _loss_function on unwrapped base model for PEFT
- Enable previously skipped test_llama_lora_kd test
- Add test config fixes for LoRA kernel compatibility

Fixes https://github.com/axolotl-ai-cloud/axolotl/issues/3206

src/axolotl/integrations/kd/kernels/models.py

@@ -72,9 +72,9 @@ def kldiv_forward_llama_like(
 
     # Only compute necessary logits, and do not upcast them to float if we are not computing the loss
     # TODO, we can optimize this further by filtering hidden_states on sequence dimension using labels != -100
-    # self.loss_function should be LigerFusedLinearKLTopKLogprobLoss
+    # self._loss_function should be LigerFusedLinearKLTopKLogprobLoss
 
-    loss = self.loss_function(
+    loss = self._loss_function(
         self.lm_head.weight,
         hidden_states,
         target_token_ids,

src/axolotl/integrations/kd/trainer.py

@@ -29,7 +29,8 @@ class AxolotlKDTrainer(AxolotlTrainer):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.model_accepts_loss_kwargs = True
-        self.model._loss_function = LigerFusedLinearKLTopKLogprobLoss(
+
+        loss_fn = LigerFusedLinearKLTopKLogprobLoss(
             self.args.kd_ce_alpha,  # hard label loss
             self.args.kd_alpha,  # kd loss
             self.args.kd_temperature,
@@ -37,6 +38,14 @@ class AxolotlKDTrainer(AxolotlTrainer):
             compute_ce_loss=bool(self.args.kd_ce_alpha),
             normalize_topk=self.args.kd_normalize_topk,
         )
+        target = self.model
+
+        # Unwrap PEFT wrapper
+        if hasattr(target, "get_base_model"):
+            target = target.get_base_model()
+
+        # Set on the actual model instance
+        target._loss_function = loss_fn
 
     def _set_signature_columns_if_needed(self):
         super()._set_signature_columns_if_needed()