Your BIOS is broken and requested that x2apic be disabled

[Fred155]

Hello

I'm getting a message from the kernel saying that:
"Your BIOS is broken and requested that x2apic be disabled. This will slightly decrease performance".
It then notes that it's falling back to xapic, and continues on without issue.
(This happens ~0.03 seconds into every boot cycle.)

My environment is:
Gigabyte Z97MX-Gaming 5 motherboard (BIOS version F5)
Intel i5 4690K (overclocked, but this issue happens with default settings in the UEFI as well)
Linux Mint 17.2 - running kernel 3.16.0-44-generic (but this issue happens with other kernels as well)
Other: Gigabyte N75TOC-2GL (graphics), G.Skill GS-F3-1866C9D-8GAB (ram), Samsung 850 Pro SSD

I can use the kernel parameter "intremap=no_x2apic_optout" to force the use of x2apic, with no visible issues, but I'm wondering what's going on to cause this in the first place.
1) Is there anyone else running linux who is getting a similar message? (just run 'dmesg | grep x2apic' in a shell)
2) Is there any known reason why this, or any bios/board would use xapic instead of x2apic, when the later is available?

Thanks

[Fred155]

I take that back... enabling x2apic is causing rare, intermittent, freezes of the mouse & keyboard, and possibly other interrupt signals. Lasting for about 5 seconds, happening once or twice per day. (strongly suspected, but difficult to 100% prove)

I presume this would not affect windows users, as I'm not aware of a way for windows to force the use of x2apic when the uefi requests for it to be disabled.

which means everyone with these boards will have a *slight*, probably imperceptible loss of speed from interrupts, but will also be open to the old xapic vulnerabilities - http://serverfault.com/questions/574486/what-are-irq-injection-attacks.

thanks gigabyte, great work.