recent patch "x86/acpi: Prevent X2APIC id 0xffffffff from being accounted"
From: Jan Beulich
Date: Fri Apr 27 2018 - 03:21:50 EST
I've just stumbled across this commit, and I'm wondering if that's actually
correct (I too have at least one system where such IDs are reported in
MADT): For offline/absent CPUs, the firmware may not know the APIC IDs
at the point MADT is built, so I think it is quite reasonable to put ~0 in
there. The ACPID spec specifically calls out that the IDs must not change
across sleep states, which implies to me that they may change across an
offline period of a CPU. IOW I think such entries still need to contribute to
the count of disabled CPUs.
I notice a similar change has been done for the xAPIC case a while ago
by you, Thomas.