Resizable BAR for Intel Arc Pro cards on boards without UEFI support

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On machines whose firmware doesn't enable Resizable BAR, Intel Arc graphics cards stay stuck with a 256 MiB window into their memory instead of exposing all of their VRAM, which matters most when the GPU is passed through to a virtual machine. Two kernel patches proposed for the Proxmox 7.0 kernel let Linux enlarge the BAR itself, with no BIOS option or UEFI hacks.

An Arc card contains its own PCIe switch, whose 8 MiB BAR0 pins the root port's memory window, so resizing the GPU's BAR2 fails. The patch releases that BAR0 so the window can grow. A second fix covers devices sitting directly on a root bus, which had their BARs released but never reassigned while the kernel reported success.

The author says the approach is heavily informed by Claude and outside their usual comfort zone, and is looking for testers; downloads are on the Proxmox forum.