Re: [tip:x86/urgent] x86/apic: Fix signedness bug in APIC ID validity checks

[Dou Liyang]

Hi Thomas,

At 04/10/2018 10:51 PM, tip-bot for Li RongQing wrote:
[...]

> x86/apic: Fix signedness bug in APIC ID validity checks
>
> The APIC ID as parsed from ACPI MADT is validity checked with the
> apic->apic_id_valid() callback, which depends on the selected APIC type.
>
> For non X2APIC types APIC IDs >= 0xFF are invalid, but values > 0x7FFFFFFF

Today when I am reading "Intel 64 Architecture x2APIC Specification", I
find that below in chapter 2.4.1:

  The APIC ID value of FFFF_FFFFH and the highest value corresponding to
  the imple-mented bit-width of the local APIC ID register in the system
  are reserved and cannot be assigned to any logical processor.

Seems, FFFF_FFFFH is also invalid for X2APIC types, Shall we also do the
validity check for X2APIC ID?

acpi_parse_x2apic()
	...
	/* Ignore invalid ID */
	if (apic_id == 0xffffffff)
		return 0;
	...

Thanks,
	dou