Назначение CONFIG_IRQ_REMAP

Supports Interrupt remapping for IO-APIC and MSI devices. To use x2apic mode in the CPU's which support x2APIC enhancements or to support platforms with CPU's having > 8 bit APIC ID, say Y.

Interrupt-remapping is part of Intel Virtualization Technology for
Directed I/O architecture
...
Interrupt-remapping architecture enables extended Interrupt Mode on x86
platforms supporting 32-bit APIC-IDs. This infrastructure allows
the existing interrupt sources such as I/OxAPICs and MSI/MSI-X devices work
seamlessly with apic-id's > 8 bits. As such, this is a pre-requisite for
enabling x2apic mode in the CPU.