[BugFix] Fix fp4 quant kernel on CUDA 12.8 (#35210)

Signed-off-by: LopezCastroRoberto <rocastro@redhat.com>

csrc/quantization/fp4/activation_nvfp4_quant_fusion_kernels.cu

@@ -107,7 +107,9 @@ __global__ void __launch_bounds__(512, VLLM_BLOCKS_PER_SM(512))
               (uint64_t(out_val.hi) << 32) | uint64_t(out_val.lo);
           reinterpret_cast<uint64_t*>(out)[outOffset >> 1] = packed64;
         } else {
-          out[inOffset] = out_val;
+          int64_t outOffset =
+              rowIdx * (numCols / CVT_FP4_ELTS_PER_THREAD) + colIdx;
+          out[outOffset] = out_val;
         }
       }
     }
@@ -140,7 +142,7 @@ void silu_and_mul_nvfp4_quant_sm1xxa(torch::Tensor& output,  // [..., d]
   int const numBlocksPerSM =
       vllm_runtime_blocks_per_sm(static_cast<int>(block.x));
 
-  int sf_n_unpadded = int(n / CVT_FP4_SF_VEC_SIZE);
+  int sf_n_unpadded = int(n / CVT_FP4_ELTS_PER_THREAD);
 
   int grid_y = vllm::div_round_up(sf_n_unpadded, static_cast<int>(block.x));
   int grid_x = std::min(

csrc/quantization/fp4/nvfp4_quant_kernels.cu

@@ -109,7 +109,8 @@ __global__ void __launch_bounds__(512, VLLM_BLOCKS_PER_SM(512))
 template <class Type, bool UE8M0_SF = false>
 __global__ void __launch_bounds__(512, VLLM_BLOCKS_PER_SM(512))
     cvt_fp16_to_fp4_sf_major(int32_t numRows, int32_t numCols,
-                             int32_t sf_n_unpadded, Type const* __restrict__ in,
+                             int32_t sf_n_unpadded, int32_t num_packed_cols,
+                             Type const* __restrict__ in,
                              float const* __restrict__ SFScale,
                              uint32_t* __restrict__ out,
                              uint32_t* __restrict__ SFout) {
@@ -131,7 +132,7 @@ __global__ void __launch_bounds__(512, VLLM_BLOCKS_PER_SM(512))
   // Iterate over all rows and cols including padded ones -
   //  ensures we visit every single scale factor address to initialize it.
   for (int rowIdx = blockIdx.x; rowIdx < numRows; rowIdx += gridDim.x) {
-    if (colIdx < sf_n_unpadded) {
+    if (colIdx < num_packed_cols) {
       PackedVec in_vec;
       int64_t inOffset = rowIdx * (numCols / CVT_FP4_ELTS_PER_THREAD) + colIdx;
 
@@ -222,7 +223,8 @@ void scaled_fp4_quant_sm1xxa(torch::Tensor const& output,
           reinterpret_cast<uint32_t*>(sf_out));
     });
   } else {
-    int grid_y = vllm::div_round_up(sf_n_unpadded, static_cast<int>(block.x));
+    int num_packed_cols = n / CVT_FP4_ELTS_PER_THREAD;
+    int grid_y = vllm::div_round_up(num_packed_cols, static_cast<int>(block.x));
     int grid_x = std::min(
         m, std::max(1, (multiProcessorCount * numBlocksPerSM) / grid_y));
     dim3 grid(grid_x, grid_y);
@@ -232,8 +234,8 @@ void scaled_fp4_quant_sm1xxa(torch::Tensor const& output,
       auto input_ptr = static_cast<cuda_type const*>(input.data_ptr());
       // NOTE: We don't support e8m0 scales at this moment.
       vllm::cvt_fp16_to_fp4_sf_major<cuda_type, false>
-          <<<grid, block, 0, stream>>>(m, n, sf_n_unpadded, input_ptr,
-                                       input_sf_ptr,
+          <<<grid, block, 0, stream>>>(m, n, sf_n_unpadded, num_packed_cols,
+                                       input_ptr, input_sf_ptr,
                                        reinterpret_cast<uint32_t*>(output_ptr),
                                        reinterpret_cast<uint32_t*>(sf_out));
     });