A kernel module and helper utility to remove PAT entries. May cause issues if used incorrectly, so proceed with caution.
Intended as a less dodgy workaround for this issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2794
Also my first kernel module and first (sort of) useful thing written in C.
The kernel module DOES NOT CARE what you give it: as long as it parses it will try to memtype_free the address range(s) you supply, even if that memory is still in use by a driver. Doing this while anything is actively using that memory might result in memory corruption. USE AT YOUR OWN RISK.
Best to unload/stop relevant drivers before running this.
Write a string like this 0x000000f81c650000-0x000000f81c651000 to /dev/pat_dealloc in a single write call, without a newline. The module will stupidly attempt to free the given range, check kernel logs.
Run pat-dealloc raw --start 0x000000f81c650000 --end 0x000000f81c651000 to accomplish the same as the example above.
Alternatively, run pat-dealloc pci --address 0000:01:00.0 to free all reserved PAT entries for the given PCI device.
You can append --load to either of these to automatically load the kernel module for you.
You will need rust set up and linux headers installed. The makefile was written for arch and might need tweaking on other distros (PRs welcome).
You will also need to re-compile the module for every new kernel you run, which can be automated with dkms or similar.
cargo build to compile the userspace helper. ./target/debug/pat-dealloc as root to run it.
cd into module and run make to compile the kernel module. Then insmod pat_dealloc.ko as root.