Fix attention mask type for Flash Attention + CP + THD (#1354)

* always have padding mask type for both flash and fused attentions
Signed-off-by: Xiaowei Ren <xren@nvidia.com>

* remove an redundant assert
Signed-off-by: Xiaowei Ren <xren@nvidia.com>

---------
Signed-off-by: Xiaowei Ren <xren@nvidia.com>

tests/pytorch/fused_attn/run_fused_attn_with_cp.py

@@ -42,7 +42,7 @@ def run_dpa_with_cp(
         "causal",
         "no_mask",
     ], f"{config.attn_mask_type} is an unsupported attention mask type!"
-    if kernel_backend == "FusedAttention" and qkv_format == "thd":
+    if qkv_format == "thd":
         if "causal" in config.attn_mask_type:
             config.attn_mask_type = "padding_causal"
         else:

transformer_engine/pytorch/attention.py

@@ -4309,14 +4309,6 @@ def attn_forward_func_with_cp(
     assert (
         qkv_format != "sbhd" or use_fused_attention
     ), "FlashAttention does not support sbhd format!"
-    assert (
-        qkv_format != "thd"
-        or not use_fused_attention
-        or attn_mask_type in ["padding", "padding_causal"]
-    ), (
-        f"Context parallelism is not supported for {attn_mask_type} mask type and "
-        f"{qkv_format} format with {'FusedAttention' if use_fused_attention else 'FlashAttention'}!"
-    )
     assert attn_bias is None or (use_fused_attention and "padding" not in attn_mask_type), (
         """Attention bias is only supported with FusedAttention and "causal" """
         """or "no_mask" mask types!"""
@@ -7878,6 +7870,9 @@ class DotProductAttention(TransformerEngineBaseModule):
             ), f"Values have head_dim = {value_layer.shape[-1]}, "
             "but expected head_dim = {self.hidden_size_per_attention_head_v}!"
 
+            if qkv_format is None:
+                qkv_format = self.qkv_format
+
             if attn_mask_type is None:
                 attn_mask_type = self.attn_mask_type
             else:
@@ -7904,9 +7899,6 @@ class DotProductAttention(TransformerEngineBaseModule):
                     graph_safe_rng_available()
                 ), "Upgrade PyTorch version to get RNG manipulation support for cuda graph capture."
 
-            if qkv_format is None:
-                qkv_format = self.qkv_format
-
             if inference_params is not None:
                 assert self.layer_number is not None, "Layer number must be set!"