Re: [patch 00/37] cpu/hotplug, x86: Reworked parallel CPU bringup

[Thomas Gleixner]

On Thu, Apr 20 2023 at 17:57, Thomas Gleixner wrote:
> On Thu, Apr 20 2023 at 07:51, Sean Christopherson wrote:
> Something like the completely untested below should just work whatever
> APIC ID the BIOS decided to dice.
>
> That might just work on SEV too without that GHCB muck, but what do I
> know.

It does not.

RDMSR(X2APIC_ID) is trapped via #VC which cannot be handled at that
point. Unfortunately the GHCB protocol does not provide a RDMSR
mechanism similar to the CPUID mechanism. Neither does the secure
firmware enforce CPUID(0xb):APICID to real APIC ID consistency.

So the hypervisor can dice the APIC IDs as long as they are consistent
with the provided ACPI/MADT table.

So no parallel startup for SEV for now.

Thanks,

        tglx