On Thu, Apr 20 2023 at 10:23, Andrew Cooper wrote: > On 20/04/2023 9:32 am, Thomas Gleixner wrote: >> I'm pondering to simply deny parallel mode if x2APIC is not there. > > I'm not sure if that will help much. Spoilsport. > Just because x2APIC is there doesn't mean it's in use. There are > several generations of Intel system which have x2APIC but also use the > opt-out bit in ACPI tables. There are some machines which have > mismatched APIC-ness settings in the BIOS->OS handover. > > There's very little you can do on the BSP alone to know for certain that > the APs come out of wait-for-SIPI already in x2APIC mode. Yeah. Reading the APIC that early is going to be entertaining too :) > One way is the ÆPIC Leak "locked into x2APIC mode" giant security > bodge. Bah. > If the system really does have a CPU with an APIC ID above 0xfe, then > chances are good that the APs come out consistently... Anything else would be really magic :)
