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Linux Module Addresses PCIe Resizable BAR Limitations for GPUs

Linux Module Addresses PCIe Resizable BAR Limitations for GPUs

First seen 12 Nov 2026, 17:55 UTC • •
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ThreatCluster AI
ThreatCluster •November 12, 2026 at 17:56 UTC
  • •The gpu-rebar-layout module enables full 32 GB Resizable BARs for GPUs on Linux.
  • •Issues arose when multiple GPUs were installed, causing POST failures due to address space limitations.
  • •The module modifies PCIe resources at boot, allowing for peer-to-peer communication between GPUs.

A new Linux kernel module, gpu-rebar-layout, has been developed to enable full 32 GB Resizable BARs for GPUs when BIOS settings are insufficient. The module is designed for systems with multiple GPUs, specifically four AMD Radeon AI PRO R9700s and two RTX 3090s, which faced issues during POST due to address space limitations. The module modifies PCIe resources at boot to ensure that the GPUs can utilize their full memory capacity, which is for enabling peer-to-peer communication between the R9700s. The initial implementation was tested on a specific machine configuration and relies on kernel internals that may change in future releases. Users are advised to read the README before loading the module due to potential compatibility issues. The situation highlights the ongoing challenges with PCIe resource allocation in Linux, particularly for high-performance computing setups.

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Timeline

2026-11-12
gpu-rebar-layout module released
The Linux kernel module was released to support full Resizable BARs for selected GPUs at boot.
github.com
2026-11-12
Article published detailing PCIe switch issues
A detailed article was published explaining the challenges faced with multiple GPUs and the need for the gpu-rebar-layout module.
News.Ycombinator

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Common questions

What is the gpu-rebar-layout module?
It is a Linux kernel module that allows GPUs to utilize their full 32 GB Resizable BARs at boot when BIOS settings are inadequate.
What systems are affected by the PCIe issues?
The issues primarily affect systems with multiple GPUs, specifically setups involving AMD Radeon AI PRO R9700s and RTX 3090s.
How does the module work?
The module modifies PCIe resources at boot, removing and rescanning devices to allocate the necessary address space for the GPUs.