Resizable BAR Comes to Haswell Motherboards Thanks to a Community UEFI Driver
Haswell owners finally have a way to get Resizable BAR running on Intel 8-series motherboards.
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A developer named roschank has released reBART, an open-source UEFI driver that enables Resizable BAR on Intel 8-series motherboards including Z87, H87, Q87, B85, Q85, and H81 models. Haswell CPUs have supported the feature since their release, but motherboard manufacturers never provided firmware updates to enable it. The developer discovered that Intel's 8-series platform code failed to map memory above 4 GB, a limitation inherited by all board makers, making the Above 4G Decoding toggle in some BIOSes ineffective.
reBART operates by allowing normal boot and then shifting the GPU's memory window past the 4 GB boundary just before the operating system loads, while redirecting the boot display to the new location. Unlike the ReBarUEFI alternative, it does not require module patching, though users must still apply a DSDT patch. Recent builds added experimental support for Intel Arc graphics cards and multi-GPU configurations.
The solution requires flashing a modified BIOS, which carries risks—at least one user reported boot failure after applying the DSDT patch. Testing has confirmed functionality with multiple Arc cards on compatible hardware, though the developer has not published performance benchmarks. Users considering this approach should be aware of the potential complications involved.
What happened
Haswell owners finally have a way to get Resizable BAR running on Intel 8-series motherboards. As spotted by Haze on X, a developer going by roschank has released reBART, an open-source UEFI driver for Z87, H87, Q87, B85, Q85, and H81 boards. Back in 2020, it was reported that Intel CPUs since Haswell support Resizable BAR, pending firmware updates from motherboard makers that never came for 8-series. The developer went digging after failing to get Above 4G Decoding working on their own B85 board, and found that Intel's 8-series platform code skips mapping memory above 4 GB altogether, something both 7-series and 9-series firmware handle.
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