NvStrapsReBar

UEFI driver to test and enable Resizable BAR on Turing graphics cards (GTX 1600, RTX 2000). Pre-Pascal cards might also work.

This is a copy of the rather popular ReBarUEFI DXE driver. ReBarUEFI enables Resizable BAR for older motherboards and chipsets without ReBAR support from the manufacturer. NvStrapsReBar was created to test Resizable BAR support for GPUs from the RTX 2000 (and GTX 1600, Turing architecture) line. Apparently for the GTX 1000 cards (Pascal architecture) the Windows driver just resets the computer during boot if the BAR size has been changed, so GTX 1000 cards still can not enable ReBAR. The Linux driver does not crash, but does not pick up the new BAR size either.

Do I need to flash a new UEFI image on the motherboard, to enable ReBAR on the GPU ?

Yes, this is how it works for Turing GPUs (GTX 1600 / RTX 2000). It's ususally the video BIOS (vBIOS) that should enable ReBAR, but the vBIOS is digitally signed and can not be modified by end-users (is locked-down). The motherboard UEFI image can also be signed or have integrity checks, but in general it is thankfully not as locked down, and users and UEFI modders still have a way to modify it.

Currently the location of the GPU on the PCI bus has to be hard-coded right into the motherboard UEFI, and so does the associated PCI-to-PCI bridge. All hard-coded values are in the header file ReBarDxe/include/LocalPciGPU.h, and all the neccesary values can be read from the CPU-Z .txt report file, so you can manually change them to match your system. Currently these settings are listed below, where all numeric values are examples only (for my computer):

#define TARGET_GPU_PCI_VENDOR_ID        0x10DEu
#define TARGET_GPU_PCI_DEVICE_ID        0x1E07u

#define TARGET_GPU_PCI_BUS              0x41u
#define TARGET_GPU_PCI_DEVICE           0x00u
#define TARGET_GPU_PCI_FUNCTION         0x00u

// PCIe config register offset 0x10
#define TARGET_GPU_BAR0_ADDRESS         UINT32_C(0x8200'0000)               // Should fall within memory range mapped by the bridge

// Secondary bus of the bridge must match the GPU bus
// Check the output form CPU-Z .txt report

#define TARGET_BRIDGE_PCI_VENDOR_ID     0x1022u
#define TARGET_BRIDGE_PCI_DEVICE_ID     0x1453u

#define TARGET_BRIDGE_PCI_BUS           0x40u
#define TARGET_BRIDGE_PCI_DEVICE        0x03u
#define TARGET_BRIDGE_PCI_FUNCTION      0x01u

// Memory range and I/O port range (base + limit) mapped to bridge
// from CPU-Z .txt report of the bridge and GPU

// PCIe config register offset 0x20
#define TARGET_BRIDGE_MEM_BASE_LIMIT  UINT32_C(0x8300'8200)                 // Should cover the GPU BAR0

// PCIe config register offset 0x1C
#define TARGET_BRIDGE_IO_BASE_LIMIT   0x8181u

See xCuri0#89 (comment) for more step-by-step details.

Rebuild the project using the instructions below (that were slightly adapted from the original ReBarUEFI project).

Credits go to the bellow github users, as I integrated and coded their findings and results:

• envytools project for the original effort on reverse-engineering the register interface for the GPUs, a very long time ago, for use by the nouveau open-source driver in Linux. Amazing how this documentation could still help us today !
• @mupuf from envytools project for bringing up the idea and the exact (low level) registers from the documentation, that enable resizable BAR
• @Xelafic for the first code samples (written in assembly!) and the first test for using the GPU STRAPS bits, documented by envytools, to select the BAR size during PCIe bring-up in UEFI code.
• @xCuri0 for great support and for the ReBarUEFI DXE driver that enables ReBAR on the motherboard, and allows intercepting and hooking into the PCIe enumeration phases in UEFI code on the motherboard.

Working GPUs

Check issue terminatorul#1 for a list of known working GPUs (and motherboards).

If you get Resizable BAR working on your Turing (or earlier) GPU, please post your system information on issue terminatorul#1 here on github, in the below format

• CPU:
• Motherboard model:
• Motherboard chipset:
• Graphics card model:
• GPU chipset:
• GPU PCI VendorID:DeviceID (check GPU-Z):
• GPU PCI subsystem IDs (check GPU-Z):
• VRAM size:
• New BAR size (GPU-Z):
• New BAR size (nvidia-smi):
• driver version:

Use command nvidia-smi -q -d memory to check the new BAR size reported by the Windows/Linux driver.

It maybe easier and more informative to post GPU-Z screenshots with the main GPU page + ReBAR page, and CPU-X with the CPU page and motherboard page screenshots. If you needed to apply more changes to make ReBAR work, please post about them as well.

Building (Windows only)

• Download and install Visual Studio 2022 Community Edition from Microsoft. Be sure to select C/C++ Desktop Development option for installation.

• Download and install Python 3. Make sure you select the option to add python to PATH during installation.

• Download and install git

• Download and install CMake

• Download and install NASM, and update environment variables NASM_PREFIX and PATH with the chosen install location. By default it is %ProgramFiles%\NASM. Set NASM_PREFIX environment variable to %ProgramFiles%\NASM\ (NOTE the backslash character \ at the end of the path), and also add %ProgramFiles%\NASM to the PATH environment variable (in Windows Settings). You can change your NASM_PREFIX and PATH variable from Start Menu | Windows Settings | System | About | Advanced Windows Settings | Environment Variables | System variables | PATH | Edit... | New...

• You can check all installed commands are available on PATH: open a new cmd console window, and run the following commands:

  python --version
  pip --version
  git --version
  nasm --version
  cmake --version
  

  If the output from any of the above commands says 'cmd-name' is not recognized as an internal or external command... you need to check PATH environment variable again. Also make sure python --version outputs version 3 and not version 2.

• Install pefile module for python:

  • Use Win+R to open a cmd window and run pip install pefile

• Get edk2 framework from github. In a cmd window run:

  git -C "%UserProfile%" clone https://github.com/tianocore/edk2.git
  git -C "%UserProfile%\edk2" submodule update --init --jobs "%Number_Of_Processors%"
  

• Build edk2. Open x86 Native Tools Command Prompt from the start menu (like in the image)

  

  and type the following commands in the resulting console window:

  • If Not Defined VSCMD_VER "%ProgramFiles%\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars32.bat"
  • ChDir "%UserProfile%\edk2"
  • edksetup.bat Rebuild

• Configure edk2. Edit file %UserProfile%\edk2\Conf\target.txt with a text editor like Notepad for example and search, in order, for the lines begining with TARGET =, TARGET_ARCH = and TOOL_CHAIN_TAG = (without any # characters -- if needed remove the leading # character from such lines, to uncomment them). Modify these lines to read:

  TARGET                = RELEASE
  TARGET_ARCH           = X64
  TOOL_CHAIN_TAG        = VS2019
  

• Get NvStrapsReBar from this repository, and place it as a subdirectory right under the edk2 directory, with the following commands:

  ChDir "%UserProfile%\edk2"
  git clone https://github.com/terminatorul/NvStrapsReBar.git
  

You can now build the UEFI DXE driver NvStrapsReBar.ffs, and the Windows executable NvStrapsReBar.exe

• To build UEFI DXE driver NvStrapsReBar.ffs, run the following commands in the x86 Native Tools Command Prompt window

  If Not Defined VSCMD_VER "%ProgramFiles%\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars32.bat"
  ChDir "%UserProfile%\edk2"
  If Not Defined EDK_TOOLS_BIN edksetup.bat
  ChDir NvStrapsReBar\ReBarDxe
  python buildffs.py
  

  The NvStrapsReBar.ffs file will be found under the directory %UserProfile%\edk2\Build\NvStrapsReBar\RELEASE_VS2019\X64\.
• To build the Windows executable NvStrapsReBar.exe, run the following commands in the x86 Native Tools Command Prompt window

  If Not Defined VSCMD_VER "%ProgramFiles%\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars32.bat"
  ChDir "%UserProfile%\edk2"
  If Not Defined EDK_TOOLS_BIN edksetup.bat
  ChDir NvStrapsRebar\ReBarState
  If Not Exist build MkDir build
  ChDir build
  cmake .. && cmake --build . --config Release
  

  The NvStrapsRebar.exe file will be found under the %UserProfile%\edk2\NvStrapsRebar\ReBarState\build\Release\ subdirectory

Updating UEFI image

The resulting NvStrapsReBar.ffs file needs to be included in the motherboard UEFI image (downloaded from the montherboard manufacturer), and the resulting image should be flashed onto the motherboard as if it were a new UEFI version for that board. See the original project ReBarUEFI for the instructions to update motherboard UEFI. Replace "ReBarUEFI.ffs" with "NvStrapsReBar.ffs" where appropriate.

So you will still have to check the README page from the original project:

• https://github.com/xCuri0/ReBarUEFI

for all the details and instructions on working with the UEFI image, and patching it if necessary (for older motherboards and chipsets).

Enable ReBAR and choose BAR size

After flashing the motherboard with the new UEFI image, you need to enable "Above 4G decoding" and disable CSM in UEFI setup, and then run NvStrapsReBar.exe as Administrator.

NvStrapsReBar.exe prompts you with a small text-based menu. You can configure 2 value for the BAR size with this tool:

• GPU-side BAR size
• PCI BAR size

Both sizes must be right for Resizable BAR to work, but maybe some newer boards can already configure PCI BAR size as expected, so maybe there is a small chance you only need to set the GPU-side value for the BAR size. But you should try and experiment with both of them, as needed.

Most people should choose the first menu option and press E to Enable auto-settings BAR size for Turing GPUs. Depending on your board, you may need to also input P at the menu prompt, to choose Target PCI BAR size, and select value 64 (for the option to configure PCI BAR for selected GPUs only). Befor quitting the menu, input S to save the changes you made to the EFI variable store, for the UEFI DXE driver to read them.

If you choose a GPU BAR size of 8 GiB for example, and a Target PCI BAR size of 4 GiB, you will get a 4 GiB BAR.

For older boards without ReBAR support from the manufacturer, you can select other values for Target PCI BAR size, to also configure other GPUs for example. Or to limit the BAR size to smaller values even if the GPU supports higher values. Depending on the motherboard UEFI, for some boards you may need to use lower values, to limit BAR size to 4 GB or 2GB for example. Even a 2 GB BAR size still gives you the benefits of Resizable BAR in most titles, and NVIDIA tends to use 1.5 GB as the default size in the Profile Inspector. There are exceptions to this 'though (for some titles that can still see improvements with the higher BAR sizes).

Using large BAR sizes

Remember you need to use the Profile Inspector to enable ReBAR per-application, and if neeeded also globally. There appears to be a fake site for the Profile Inspector, so always downloaded it from github, or use the link above.