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

Andrew Cooper
2023-04-19T13:51:20Z

On 19/04/2023 2:43 pm, Thomas Gleixner wrote:
> On Wed, Apr 19 2023 at 14:38, Thomas Gleixner wrote:
>> On Wed, Apr 19 2023 at 11:38, Thomas Gleixner wrote:
>> IOW, the BIOS assignes random numbers to the AP APICs for whatever
>> raisins, which leaves the parallel startup low level code up a creek
>> without a paddle, except for actually reading the APICID back from the
>> APIC. *SHUDDER*
> So Andrew just pointed out on IRC that this might be related to the
> ancient issue of the 3-wire APIC bus where IO/APIC and APIC shared the
> ID space, but that system is definitely post 3-wire APIC :)

Doesn't mean the BIOS code was updated adequately following that.

What I'm confused by is why this system boots in the first place.  I can
only think that's is a system which only has 4-bit APIC IDs, and happens
to function when bit 4 gets truncated off the top of the SIPI destination...

~Andrew