[sgl-kernel] support flashmla libtorch (#11717)

sgl-kernel/csrc/flashmla_extension.cc

@@ -0,0 +1,46 @@
+/* Copyright 2025 SGLang Team. All Rights Reserved.
+
+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.
+==============================================================================*/
+
+#include <torch/all.h>
+#include <torch/library.h>
+
+#include "sgl_kernel_ops.h"
+
+TORCH_LIBRARY_FRAGMENT(sgl_kernel, m) {
+  /*
+   * From FlashMLA
+   */
+  m.def(
+      "get_mla_decoding_metadata(Tensor seqlens_k, int num_q_tokens_per_head_k, int h_k, int? h_q, bool "
+      "is_fp8_kvcache, int? topk) -> Tensor[]");
+  m.impl("get_mla_decoding_metadata", torch::kCUDA, &get_mla_decoding_metadata);
+
+  m.def(
+      "fwd_kvcache_mla(Tensor q, Tensor kv_cache, int head_size_v, Tensor seqlens_k, Tensor block_table, float "
+      "softmax_scale, bool is_causal, Tensor tile_scheduler_metadata, Tensor num_splits, bool is_fp8, Tensor? indices) "
+      "-> Tensor[]");
+  m.impl("fwd_kvcache_mla", torch::kCUDA, &fwd_kvcache_mla);
+
+  m.def(
+      "dense_prefill_fwd(Tensor workspace_buffer, Tensor q, Tensor k, Tensor v, Tensor cumulative_seqlen_q, Tensor "
+      "cumulative_seqlen_kv, Tensor o, Tensor lse, int mask_mode_code, float softmax_scale, int max_seqlen_q, int "
+      "max_seqlen_kv, bool is_varlen) -> ()");
+  m.impl("dense_prefill_fwd", torch::kCUDA, &FMHACutlassSM100FwdRun);
+
+  m.def("sparse_prefill_fwd(Tensor q, Tensor kv, Tensor indices, float sm_scale, int d_v) -> Tensor[]");
+  m.impl("sparse_prefill_fwd", torch::kCUDA, &sparse_prefill_fwd);
+}
+
+REGISTER_EXTENSION(flashmla_ops)