On 02.02.26 12:35, Andrew Cooper wrote: > On 02/02/2026 9:51 am, Shashank Balaji wrote: >> Interrupt remapping is an architectural dependency of x2apic, which is >> already >> enabled in the defconfig. > > There is no such dependency. VMs for example commonly have x2APIC and > no IOMMU, and even native system with fewer than 254 CPUs does not need > interrupt remapping for IO-APIC interrupts to function correctly. >
It is theoretically possible with less than 254 CPUs, and that is why virtualization uses it, but the Intel SDM clearly states: "Routing of device interrupts to local APIC units operating in x2APIC mode requires use of the interrupt-remapping architecture specified in the Intel® Virtualization Technology for Directed I/O (Revision 1.3 and/or later versions)." IIRC, ignoring this would move us into undefined behaviour space that may work on some system and did not on others. Jan -- Siemens AG, Foundational Technologies Linux Expert Center
