Remove unused code and update README (#2828)

integration/xgboost/encryption_plugins/README.md

@@ -1,23 +1,38 @@
 # XGBoost plugins
 
 
-## Install required dependencies for CUDA plugin
-If you want to build CUDA plugin, you need to install the following libraries:
-Require `libgmp-dev`, CUDA runtime >= 12.1, CUDA driver >= 12.1, NVIDIA GPU Driver >= 535
+## Install required dependencies for building CUDA plugin
+If you want to build the CUDA plugin on your own, you need to install the following libraries:
+Require `libgmp3-dev`, CMake>=3.19, CUDA runtime >= 12.1, CUDA driver >= 12.1, NVIDIA GPU Driver >= 535
 Compute Compatibility >= 7.0
 
-## Build instructions
+On the building site:
+0. Install GPU Driver >= 535, CUDA runtime >= 12.1, CUDA driver >= 12.1
+1. Install `libgmp3-dev`, gcc, CMake
+2. Clone the NVFlare main branch and update the submodule
+    ```
+    git clone https://github.com/NVIDIA/NVFlare.git \
+    && cd NVFlare/integration/xgboost/encryption_plugins \
+    && git submodule update --init --recursive
+    ```
+3. Under integration/xgboost/encryption_plugins, run the build commands
+    ```
+    mkdir build
+    cd build
+    cmake ..
+    make
+    ```
 
-```
-mkdir build
-cd build
-cmake ..
-make
-```
+> **_NOTE:_**  You can pass option to cmake to disable the build of CUDA plugin
+> if you don't have the environment: ```cmake -DBUILD_CUDA_PLUGIN=OFF ..```
 
-## Disable build of CUDA plugin
-You can pass option to cmake to disable the build of CUDA plugin if you don't have the environment:
-```
-cmake -DBUILD_CUDA_PLUGIN=OFF ..
-```
 
+## How to run with CUDA plugin
+For each client site:
+
+0. Copy the pre-built ".so" file to each site
+1. Make sure you have installed required dependencies: GPU Driver >= 535, CUDA runtime >= 12.1, CUDA driver >= 12.1, `libgmp3-dev`
+2. Update the site local resource.json to point to the ".so" file
+
+For handling these complex environment, we recommend you build a docker image so every
+client site can just use it.

integration/xgboost/encryption_plugins/cuda_plugin/src/cuda_plugin.h

@@ -215,14 +215,10 @@ class CUDAPlugin: public LocalPlugin {
 
       Buffer result = createBuffer(true, h_ptr, key_size, rand_seed, rand_seed_size, d_ciphers_ptr, mem_size);
 
-      void* buffer = malloc(mem_size);
-      cudaMemcpy(buffer, d_ciphers_ptr, mem_size, cudaMemcpyDeviceToHost);
       cudaFree(d_plains_ptr);
       cudaFree(d_ciphers_ptr);
       free(h_ptr);
 
-      //Buffer result(buffer, mem_size, true);
-
       return result;
     }