From 34cb8e28425dc50b107466ea212fd8dd80422998 Mon Sep 17 00:00:00 2001
From: nohup <fingalpeng@gmail.com>
Date: Fri, 15 May 2026 16:42:33 +0800
Subject: [PATCH] fix(sgl-kernel): sm90 compile flashmla failed (#24130)

---
 sgl-kernel/cmake/flashmla.cmake       | 42 +++++++++++++++++----------
 sgl-kernel/csrc/flashmla_extension.cc |  2 ++
 2 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/sgl-kernel/cmake/flashmla.cmake b/sgl-kernel/cmake/flashmla.cmake
index 935cb21a3..b67ace6af 100644
--- a/sgl-kernel/cmake/flashmla.cmake
+++ b/sgl-kernel/cmake/flashmla.cmake
@@ -17,6 +17,8 @@ set(FLASHMLA_CUDA_FLAGS
     "-Xcudafe=--diag_suppress=177"   # variable was declared but never referenced
 )
 
+set(FLASHMLA_ENABLE_SM100 OFF)
+
 # The FlashMLA kernels only work on hopper and require CUDA 12.4 or later.
 # Only build FlashMLA kernels if we are building for something compatible with
 # sm90a
@@ -29,6 +31,7 @@ if(${CUDA_VERSION} VERSION_GREATER 12.8)
     list(APPEND FLASHMLA_CUDA_FLAGS
         "-gencode=arch=compute_100a,code=sm_100a"
     )
+    set(FLASHMLA_ENABLE_SM100 ON)
 endif()
 if(${CUDA_VERSION} VERSION_GREATER_EQUAL "13.0")
     # Patch FlashMLA sources for SM103a support.
@@ -113,33 +116,40 @@ set(FlashMLA_SOURCES
     ${repo-flashmla_SOURCE_DIR}/csrc/sm90/prefill/sparse/instantiations/phase1_k576.cu
     ${repo-flashmla_SOURCE_DIR}/csrc/sm90/prefill/sparse/instantiations/phase1_k576_topklen.cu
 
-    # sm100 dense prefill/bwd.
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/dense/fmha_cutlass_fwd_sm100.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/dense/fmha_cutlass_bwd_sm100.cu
-
-    # sm100 sparse prefill.
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head64/instantiations/phase1_k512.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head64/instantiations/phase1_k576.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head128/instantiations/phase1_k512.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head128/instantiations/phase1_k576.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd_for_small_topk/head128/instantiations/phase1_prefill_k512.cu
-
-    # sm100 sparse decode.
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/decode/head64/instantiations/v32.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/decode/head64/instantiations/model1.cu
-    ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd_for_small_topk/head128/instantiations/phase1_decode_k512.cu
-
     ${repo-flashmla_SOURCE_DIR}/csrc/extension/sm90/dense_fp8/dense_fp8_python_api.cpp
     ${repo-flashmla_SOURCE_DIR}/csrc/extension/sm90/dense_fp8/flash_fwd_mla_fp8_sm90.cu
     ${repo-flashmla_SOURCE_DIR}/csrc/extension/sm90/dense_fp8/flash_fwd_mla_metadata.cu
 )
 
+if(FLASHMLA_ENABLE_SM100)
+    list(APPEND FlashMLA_SOURCES
+        # sm100 dense prefill/bwd.
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/dense/fmha_cutlass_fwd_sm100.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/dense/fmha_cutlass_bwd_sm100.cu
+
+        # sm100 sparse prefill.
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head64/instantiations/phase1_k512.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head64/instantiations/phase1_k576.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head128/instantiations/phase1_k512.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd/head128/instantiations/phase1_k576.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd_for_small_topk/head128/instantiations/phase1_prefill_k512.cu
+
+        # sm100 sparse decode.
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/decode/head64/instantiations/v32.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/decode/head64/instantiations/model1.cu
+        ${repo-flashmla_SOURCE_DIR}/csrc/sm100/prefill/sparse/fwd_for_small_topk/head128/instantiations/phase1_decode_k512.cu
+    )
+endif()
+
 Python_add_library(flashmla_ops MODULE USE_SABI ${SKBUILD_SABI_VERSION} WITH_SOABI ${FlashMLA_SOURCES})
 target_compile_options(flashmla_ops PRIVATE
     $<$<COMPILE_LANGUAGE:CXX>:-std=c++20>
     $<$<COMPILE_LANGUAGE:CUDA>:-std=c++20>
     $<$<COMPILE_LANGUAGE:CUDA>:${FLASHMLA_CUDA_FLAGS}>
 )
+if(FLASHMLA_ENABLE_SM100)
+    target_compile_definitions(flashmla_ops PRIVATE FLASHMLA_ENABLE_SM100)
+endif()
 target_include_directories(flashmla_ops PRIVATE
     ${repo-flashmla_SOURCE_DIR}/csrc
     ${repo-flashmla_SOURCE_DIR}/csrc/kerutils/include
diff --git a/sgl-kernel/csrc/flashmla_extension.cc b/sgl-kernel/csrc/flashmla_extension.cc
index 8236c8867..12b09524a 100644
--- a/sgl-kernel/csrc/flashmla_extension.cc
+++ b/sgl-kernel/csrc/flashmla_extension.cc
@@ -36,11 +36,13 @@ TORCH_LIBRARY_FRAGMENT(sgl_kernel, m) {
       "-> Tensor[]");
   m.impl("fwd_kvcache_mla", torch::kCUDA, &fwd_kvcache_mla);
 
+#ifdef FLASHMLA_ENABLE_SM100
   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);
+#endif
 
   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);