On Sun, Nov 08, 2020 at 06:34:55PM +0000, David Woodhouse wrote: > > > > When we do interrupt remapping support in guest which would be required > > if we support x2apic in guest, I think this is something we should look into more > > carefully to make this work. > > No, interrupt remapping is not required for X2APIC in guests > > They can have X2APIC and up to 32768 CPUs without needing interrupt How is this made available today without interrupt remapping? I thought without IR, the destination ID is still limited to only 8 bits? On native, even if you have less than 255 cpu's but the APICID are sparsly distributed due to platform rules, the x2apic id could be more than 8 bits. Which is why the spec requires IR when x2apic is enabled. > remapping at all. Only if they want more than 32768 vCPUs, or to do > nested virtualisation and actually remap for the benefit of *their* > (L2+) guests would they need IR.
