D3: add swa_lens parameter to FmhaKernel (in-kernel masking TBD)

dsv4/kernels/attention/fmha.py

@@ -131,6 +131,9 @@ class FmhaKernel:
         # CuTeDSL doesn't support None parameters in @cute.kernel.
         if const_expr(lse is None):
             lse = cute.make_tensor(c.iterator, cute.make_layout((1,), stride=(0,)))
+        if const_expr(swa_lens is None):
+            # No SWA masking — pass a dummy tensor
+            swa_lens = cute.make_tensor(c.iterator, cute.make_layout((1,), stride=(0,)))
         # Grid: (M_tiles, 1, batch) where M = n_h * T packed into M dimension
         # For single-head (n_h=1): grid=(1,1,1) — backward compatible
         self._kernel(qk_mma,pv_mma,tma_q,mQ,tma_k,mK,tma_v,mV,tma_c,mC,self.cluster_layout_vmnk,self.q_smem_s,self.k_smem_s,self.v_smem_s,self.p_tmem_s,self.p_smem_s,self.c_smem_s,self.epi_tile,lse,swa_lens).launch(grid=(1,1,self.batch_size),block=[self.threads_per_cta,1,1],stream=stream)