A shame that the one machine I have that I wish to use ReBar on I cannot. The Mac Pro 2019 has a complicated PCI-E topology with PCI-E switches (all bar 2 PCI-E slots on the system go via the PCI-E switch topology) and no ability to tune/enable settings like sub-numa clustering or ReBar. Paired with a signed EFI and the T2 controller things look bleak for getting the most performance out of that system.
It would be pretty neat to get the most out of an NVIDIA GPU in Linux on this platform