X2APIC support

[Andriy Gapon]

On 04/09/2016 18:14, Konstantin Belousov wrote:
> On Sun, Sep 04, 2016 at 11:19:16AM +0300, Andriy Gapon wrote:
>> Kostik, I see one strange thing which is common to both successful and
>> unsuccessful configurations.  All "SMP: Added CPU..." lines have "AP" in them.
>> It seems like the platform does not tell explicitly tell which CPU is the BSP,
>> see cpu_add() function.  This can break quite a few assumption.  And I am not
>> even sure how the successful scenario works.
>> Ah... I see that there is a backup code in cpu_mp_start() where boot_cpu_id is
>> set based on the current CPU's Local APIC ID.  I suspect then that this
>> information is incorrect in the failing case.
>>
> Well, there is no easy way to read the LAPIC Id of BSP before LAPICs
> are initialized. BIOS might reprogram LAPIC Ids, so reading from
> CPUID[1].EBX[31:24] might return incorrect data. Even more incorrect
> it might be in the x2APIC state, since 8 bits are not enough for 32bit
> x2APIC Id.

Hmm, I am not sure how what you are saying here is relevant to the problem.
I believe that cpu_mp_start() is executed (on the BSP) after the BSP's LAPIC is
initialized.  So, the code should just work.

My theory was that the BSP's LAPIC ID was incorrectly programmed by BIOS (firmware).

-- 
Andriy Gapon