diff --git a/AMSS_NCKU_source/bssn_cuda_step.C b/AMSS_NCKU_source/bssn_cuda_step.C
index 2b3d08e..3950a2e 100644
--- a/AMSS_NCKU_source/bssn_cuda_step.C
+++ b/AMSS_NCKU_source/bssn_cuda_step.C
@@ -138,6 +138,111 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
         }
       };
 
+  auto ensure_stage_device_var_list =
+      [&](Block *cg, MyList<var> *var_list) {
+        const int n = cg->shape[0] * cg->shape[1] * cg->shape[2];
+        while (var_list)
+        {
+          double *host_ptr = cg->fgfs[var_list->data->sgfn];
+          if (!bssn_gpu_find_device_buffer(host_ptr) &&
+              bssn_gpu_stage_upload_buffer(host_ptr, n))
+          {
+            cerr << "GPU state ensure failure: lev=" << lev
+                 << " var=" << var_list->data->name
+                 << " bbox=(" << cg->bbox[0] << ":" << cg->bbox[3] << ","
+                 << cg->bbox[1] << ":" << cg->bbox[4] << ","
+                 << cg->bbox[2] << ":" << cg->bbox[5] << ")" << endl;
+            ERROR = 1;
+            break;
+          }
+          var_list = var_list->next;
+        }
+      };
+
+  auto refresh_synced_device_regions =
+      [&](Block *cg, MyList<var> *var_list, Parallel::SyncCache &cache) {
+        std::vector<Parallel::gridseg *> local_segments;
+        for (int node = 0; node < cache.cpusize; ++node)
+        {
+          MyList<Parallel::gridseg> *seg = cache.combined_dst[node];
+          while (seg)
+          {
+            if (seg->data && seg->data->Bg == cg)
+              local_segments.push_back(seg->data);
+            seg = seg->next;
+          }
+        }
+
+        if (local_segments.empty())
+          return;
+
+        const int n = cg->shape[0] * cg->shape[1] * cg->shape[2];
+        while (var_list)
+        {
+          double *host_ptr = cg->fgfs[var_list->data->sgfn];
+          if (!bssn_gpu_find_device_buffer(host_ptr))
+          {
+            if (bssn_gpu_stage_upload_buffer(host_ptr, n))
+            {
+              cerr << "GPU sync refresh upload failure: lev=" << lev
+                   << " var=" << var_list->data->name
+                   << " bbox=(" << cg->bbox[0] << ":" << cg->bbox[3] << ","
+                   << cg->bbox[1] << ":" << cg->bbox[4] << ","
+                   << cg->bbox[2] << ":" << cg->bbox[5] << ")" << endl;
+              ERROR = 1;
+              break;
+            }
+          }
+          else
+          {
+            for (size_t i = 0; i < local_segments.size(); ++i)
+            {
+              Parallel::gridseg *seg = local_segments[i];
+              if (bssn_gpu_stage_upload_region(host_ptr,
+                                               cg->shape,
+                                               cg->bbox,
+                                               cg->bbox + dim,
+                                               seg->shape,
+                                               seg->llb))
+              {
+                cerr << "GPU sync region refresh failure: lev=" << lev
+                     << " var=" << var_list->data->name
+                     << " bbox=(" << cg->bbox[0] << ":" << cg->bbox[3] << ","
+                     << cg->bbox[1] << ":" << cg->bbox[4] << ","
+                     << cg->bbox[2] << ":" << cg->bbox[5] << ")" << endl;
+                ERROR = 1;
+                break;
+              }
+            }
+            if (ERROR)
+              break;
+          }
+          var_list = var_list->next;
+        }
+      };
+
+  auto refresh_stage_device_after_sync =
+      [&](MyList<var> *var_list, Parallel::SyncCache &cache) {
+        MyList<Patch> *patch_it = GH->PatL[lev];
+        while (patch_it)
+        {
+          MyList<Block> *block_it = patch_it->data->blb;
+          while (block_it)
+          {
+            Block *cg = block_it->data;
+            if (myrank == cg->rank)
+              refresh_synced_device_regions(cg, var_list, cache);
+
+            if (block_it == patch_it->data->ble)
+              break;
+            block_it = block_it->next;
+          }
+          if (ERROR)
+            break;
+          patch_it = patch_it->next;
+        }
+      };
+
   MyList<Patch> *Pp = GH->PatL[lev];
   while (Pp)
   {
@@ -182,7 +287,8 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
   Parallel::AsyncSyncState async_pre;
   Parallel::Sync_start(GH->PatL[lev], SynchList_pre, Symmetry, sync_cache_pre[lev], async_pre);
   Parallel::Sync_finish(sync_cache_pre[lev], async_pre, SynchList_pre, Symmetry);
-  bssn_gpu_clear_cached_device_buffers();
+  if (!ERROR)
+    refresh_stage_device_after_sync(SynchList_pre, sync_cache_pre[lev]);
 
   MPI_Wait(&err_req_pre, MPI_STATUS_IGNORE);
   if (ERROR)
@@ -234,7 +340,7 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
         Block *cg = BP->data;
         if (myrank == cg->rank)
         {
-          stage_upload_var_list(cg, SynchList_pre);
+          ensure_stage_device_var_list(cg, SynchList_pre);
           if (gpu_rhs(CALLED_BY_STEP, myrank, RHS_PARA_CALLED_THEN))
             ERROR = 1;
 
@@ -270,7 +376,8 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
     Parallel::AsyncSyncState async_cor;
     Parallel::Sync_start(GH->PatL[lev], SynchList_cor, Symmetry, sync_cache_cor[lev], async_cor);
     Parallel::Sync_finish(sync_cache_cor[lev], async_cor, SynchList_cor, Symmetry);
-    bssn_gpu_clear_cached_device_buffers();
+    if (!ERROR && iter_count < 3)
+      refresh_stage_device_after_sync(SynchList_cor, sync_cache_cor[lev]);
 
     MPI_Wait(&err_req_cor, MPI_STATUS_IGNORE);
     if (ERROR)
diff --git a/AMSS_NCKU_source/bssn_gpu.cu b/AMSS_NCKU_source/bssn_gpu.cu
index bcdf57e..fc99f64 100644
--- a/AMSS_NCKU_source/bssn_gpu.cu
+++ b/AMSS_NCKU_source/bssn_gpu.cu
@@ -847,6 +847,73 @@ int bssn_gpu_stage_zero_buffer(const double *host_ptr, int count)
 	return prepare_owned_buffer(host_ptr, static_cast<size_t>(count), true) ? 0 : 1;
 }
 
+int bssn_gpu_stage_upload_region(const double *host_ptr,
+                                 const int *full_shape,
+                                 const double *full_llb,
+                                 const double *full_uub,
+                                 const int *region_shape,
+                                 const double *region_llb)
+{
+	if (!host_ptr || !full_shape || !full_llb || !full_uub || !region_shape || !region_llb)
+		return 1;
+
+	const double *device_ptr = bssn_gpu_find_device_buffer(host_ptr);
+	if (!device_ptr)
+		return 1;
+
+	int start[3] = {0, 0, 0};
+	for (int i = 0; i < 3; ++i)
+	{
+		if (full_shape[i] <= 0 || region_shape[i] <= 0)
+			return 1;
+
+#ifdef Vertex
+#ifdef Cell
+#error Both Cell and Vertex are defined
+#endif
+		const double dx = (full_uub[i] - full_llb[i]) / static_cast<double>(full_shape[i] - 1);
+		start[i] = static_cast<int>((region_llb[i] - full_llb[i]) / dx + 0.4);
+#else
+#ifdef Cell
+		const double dx = (full_uub[i] - full_llb[i]) / static_cast<double>(full_shape[i]);
+		start[i] = static_cast<int>((region_llb[i] - full_llb[i]) / dx + 0.4);
+#else
+#error Not define Vertex nor Cell
+#endif
+#endif
+
+		if (start[i] < 0 || start[i] + region_shape[i] > full_shape[i])
+			return 1;
+	}
+
+	cudaMemcpy3DParms parms = {};
+	parms.srcPtr = make_cudaPitchedPtr(const_cast<double *>(host_ptr),
+	                                   static_cast<size_t>(full_shape[0]) * sizeof(double),
+	                                   static_cast<size_t>(full_shape[0]),
+	                                   static_cast<size_t>(full_shape[1]));
+	parms.dstPtr = make_cudaPitchedPtr(const_cast<double *>(device_ptr),
+	                                   static_cast<size_t>(full_shape[0]) * sizeof(double),
+	                                   static_cast<size_t>(full_shape[0]),
+	                                   static_cast<size_t>(full_shape[1]));
+	parms.srcPos = make_cudaPos(static_cast<size_t>(start[0]) * sizeof(double),
+	                            static_cast<size_t>(start[1]),
+	                            static_cast<size_t>(start[2]));
+	parms.dstPos = parms.srcPos;
+	parms.extent = make_cudaExtent(static_cast<size_t>(region_shape[0]) * sizeof(double),
+	                               static_cast<size_t>(region_shape[1]),
+	                               static_cast<size_t>(region_shape[2]));
+	parms.kind = cudaMemcpyHostToDevice;
+
+	cudaError_t err = cudaMemcpy3D(&parms);
+	if (err != cudaSuccess)
+	{
+		cerr << "cudaMemcpy3D(H2D region) failed: " << cudaGetErrorString(err) << endl;
+		return 1;
+	}
+
+	return 0;
+}
+
 __global__ void test_const_address(double * testd){
 	int _t = blockIdx.x*blockDim.x+threadIdx.x;
 	if(_t == 0)
diff --git a/AMSS_NCKU_source/bssn_gpu.h b/AMSS_NCKU_source/bssn_gpu.h
index d69e8d0..19333c0 100644
--- a/AMSS_NCKU_source/bssn_gpu.h
+++ b/AMSS_NCKU_source/bssn_gpu.h
@@ -71,6 +71,12 @@ const double *bssn_gpu_find_device_buffer(const double *host_ptr);
 void bssn_gpu_register_device_buffer(const double *host_ptr, const double *device_ptr);
 int bssn_gpu_stage_upload_buffer(const double *host_ptr, int count);
 int bssn_gpu_stage_zero_buffer(const double *host_ptr, int count);
+int bssn_gpu_stage_upload_region(const double *host_ptr,
+                                 const int *full_shape,
+                                 const double *full_llb,
+                                 const double *full_uub,
+                                 const int *region_shape,
+                                 const double *region_llb);
 
 /** Init GPU side data in GPUMeta. */
 // void init_fluid_meta_gpu(GPUMeta *gpu_meta);