soc/intel/common: Fix invalid MADT entries creation

commit f8ac3dda02f22ebf857efb5b845db97f00598f7d ("soc/intel/common:
Order the CPUs based on their APIC IDs") sort algorithnm walks all the
`cpu_info' entries without discarding empty ones.  Since `cpu_info' is
not initialized, the data that is used is undefined and it generally
results in the creation of invalid `Local x2APIC' entries in the
MADT ("APIC") ACPI table.

Depending on the X2APIC ID value the Linux kernel behavior
changes (cf. arch/x86/kernel/acpi/boot.c::acpi_register_lapic()):
1. If (int)ID >= MAX_LOCAL_APIC (32768), the Linux kernel discards the
   entry with the "skipped apicid that is too big" INFO level
   message.
2. If (int)ID < MAX_LOCAL_APIC (32768) (including negative) this data
   is taken into account and it can lead to undesirable behavior such
   as core being disabled as (cf. "native_cpu_up: bad cpu" ERROR
   kernel message).

TEST=Verified the MADT does not contain any invalid entries on rex.

Change-Id: I19c7aa51f232bf48201bd6d28f108e9120a21f7e
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77615
Reviewed-by: Bora Guvendik <bora.guvendik@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Wonkyu Kim <wonkyu.kim@intel.com>

0 files changed, 0 insertions, 0 deletions