Is there a way of mapping an RMRR to a device easily? (Lspci -vv maybe?)
It is Unhelpful that Xen refuses PCI passthrough because of an RMRR but doesn't say what it is shared with.
In this case it was a USB controller - I guessed that it might be the USB legacy support on the motherboard USB ports, and disabling of the legacy support in the BIOS enabled the addon card to be passed through.
It's still annoying, however, as Xen knows which devices are sharing resources but doesn't seem to have an easy way to say so.
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