Good question. We have a mechanism to load an additional DSDT (see Documentation/acpi/dsdt-overriding.txt), also some methods can be overridden (method-customizing.txt) but I'm not sure about DMAR table. At least ACPI specification doesn't say it's possible to use like this. I think you may hack your kernel and try to do such, but would it be upstreamable?

Good question. We have a mechanism to load an additional DSDT (see Documentation/acpi/dsdt-overriding.txt), also some methods can be overridden (method-customizing.txt) but I'm not sure about DMAR table. At least ACPI specification doesn't say it's possible to use like this. I think you may hack your kernel and try to do such, but would it be upstreamable?

UPDATE. Oh, this one looks promising: Documentation/acpi/initrd_table_override.txt